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Cgu::Thread::TaskManager Class Reference

A thread-pool class for managing tasks in multi-threaded programs. More...

`#include <c++-gtk-utils/task_manager.h>`

## Classes
class | IncHandle
| A scoped handle for exception safe incrementing of the maximum number of threads that a TaskManager object will run. More...

## Public Types
enum | StopMode { wait_for_running, wait_for_all }

## Public Member Functions
| TaskManager (const TaskManager &)=delete
TaskManager & | operator= (const TaskManager &)=delete
unsigned int | get_max_threads () const
unsigned int | get_min_threads () const
unsigned int | get_used_threads () const
unsigned int | get_tasks () const
void | set_max_threads (unsigned int max)
void | change_max_threads (int delta)
unsigned int | get_idle_time () const
void | set_idle_time (unsigned int idle)
bool | get_blocking () const
void | set_blocking (bool blocking)
StopMode | get_stop_mode () const
void | set_stop_mode (StopMode mode)
void | stop_all ()
void | add_task (const Callback::Callback *task)
void | add_task (std::unique_ptr< const Callback::Callback > task, std::unique_ptr< const Callback::Callback > fail)
template<class Task , class = typename std::enable_if<!std::is_convertible<typename std::remove_reference<Task>::type, const Callback::Callback*>::value>::type>
void | add_task (Task &&task)
template<class Task , class Fail , class = typename std::enable_if<!std::is_convertible<Task, std::unique_ptr<const Callback::Callback>>::value && !std::is_convertible<Fail, std::unique_ptr<const Callback::Callback>>::value>::type>
void | add_task (Task &&task, Fail &&fail)
bool | is_error () const
template<class Ret , class... Params, class... Args, class T >
Cgu::SharedLockPtr < Cgu::AsyncResult< Ret > > | make_task_result (T &t, Ret(T::*func)(Params...), Args &&...args)
template<class Ret , class... Params, class... Args, class T >
void | make_task_when_full (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, Cgu::Releaser *when_releaser, std::unique_ptr< const Cgu::Callback::Callback > fail, Cgu::Releaser *fail_releaser, gint priority, GMainContext *context, T &t, Ret(T::*func)(Params...), Args &&...args)
template<class Ret , class... Params, class... Args, class T >
void | make_task_when (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, GMainContext *context, T &t, Ret(T::*func)(Params...), Args &&...args)
template<class Ret , class... Params, class... Args, class T >
Cgu::SharedLockPtr < Cgu::AsyncResult< Ret > > | make_task_result (const T &t, Ret(T::*func)(Params...) const, Args &&...args)
template<class Ret , class... Params, class... Args, class T >
void | make_task_when_full (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, Cgu::Releaser *when_releaser, std::unique_ptr< const Cgu::Callback::Callback > fail, Cgu::Releaser *fail_releaser, gint priority, GMainContext *context, const T &t, Ret(T::*func)(Params...) const, Args &&...args)
template<class Ret , class... Params, class... Args, class T >
void | make_task_when (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, GMainContext *context, const T &t, Ret(T::*func)(Params...) const, Args &&...args)
template<class Ret , class... Params, class... Args>
Cgu::SharedLockPtr < Cgu::AsyncResult< Ret > > | make_task_result (Ret(*func)(Params...), Args &&...args)
template<class Ret , class... Params, class... Args>
void | make_task_when_full (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, Cgu::Releaser *when_releaser, std::unique_ptr< const Cgu::Callback::Callback > fail, Cgu::Releaser *fail_releaser, gint priority, GMainContext *context, Ret(*func)(Params...), Args &&...args)
template<class Ret , class... Params, class... Args>
void | make_task_when (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, GMainContext *context, Ret(*func)(Params...), Args &&...args)
template<class Ret , class Func >
Cgu::SharedLockPtr < Cgu::AsyncResult< Ret > > | make_task_result (Func &&f)
template<class Ret , class Func >
void | make_task_when_full (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, Cgu::Releaser *when_releaser, std::unique_ptr< const Cgu::Callback::Callback > fail, Cgu::Releaser *fail_releaser, gint priority, GMainContext *context, Func &&func)
template<class When , class Fail , class Func , class = typename std::enable_if<!std::is_convertible<When, std::unique_ptr<const Callback::CallbackArg<const typename std::result_of<Func()>::type&>>>::value && !std::is_convertible<Fail, std::unique_ptr<const Callback::Callback>>::value>::type>
void | make_task_when_full (When &&when, Cgu::Releaser *when_releaser, Fail &&fail, Cgu::Releaser *fail_releaser, gint priority, GMainContext *context, Func &&func)
template<class Ret , class Func >
void | make_task_when (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, GMainContext *context, Func &&f)
template<class When , class Func , class = typename std::enable_if<!std::is_convertible<When, std::unique_ptr<const Callback::CallbackArg<const typename std::result_of<Func()>::type&>>>::value>::type>
void | make_task_when (When &&when, GMainContext *context, Func &&func)
template<class Ret , class Func >
void | make_task_compose (Func &&f, GMainContext *context, std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when)
template<class Func , class When , class = typename std::enable_if<!std::is_convertible<When, std::unique_ptr<const Callback::CallbackArg<const typename std::result_of<Func()>::type&>>>::value>::type>
void | make_task_compose (Func &&func, GMainContext *context, When &&when)
| TaskManager (unsigned int max=8, unsigned int min=0, unsigned int idle=10000, bool blocking=true, StopMode mode=TaskManager::wait_for_all)
| ~TaskManager ()

## Detailed Description

A thread-pool class for managing tasks in multi-threaded programs.

See Also
  Cgu::Thread::Future Cgu::AsyncResult Cgu::AsyncQueueDispatch Cgu::Callback::post() Cgu::Thread::TaskManager::IncHandle

Cgu::Thread::Future operates on the principle of there being one worker thread per task. In some cases however, it may be better to have a limited pool of worker threads executing a larger number of tasks. This class implements this approach via a thread pool.

One common approach for thread pools of this kind is to set the maximum number of threads to the number of cores, or some number less than the number of cores, available on the local machine. How that can be determined is system specific (on linux it can be obtained by, for example, counting the 'processor' fields in /proc/cpuinfo or by using sysconf with the glibc extension for _SC_NPROCESSORS_ONLN). From version 2.36, glib has a g_get_num_processors() function. From gcc-4.7, C++11's std::thread::hardware_concurrency() static member function is also available.

The most general way of creating a new task is to call TaskManager::add_task() with a callable object (such as a lambda expression or the return value of std::bind) which returns void, although add_task() will also take a Callback::Callback object. Where the task needs to provide a result, two approaches can be adopted. First, the task callback can have a Cgu::AsyncResult object held by Cgu::SharedLockPtr (or by std::shared_ptr having a thread safe reference count) bound to it. Alternatively, a task can provide a result asynchronously to a glib main loop by calling Cgu::Callback::post() when it is ready to do so. The TaskManager::make_task_result(), TaskManager::make_task_when(), TaskManager::make_task_when_full() and TaskManager::make_task_compose() convenience wrapper methods are provided which will set this up for you (including constructing appropriate task callbacks). This would normally be done by passing one of those functions a callable object which returns a value, such as a lambda expression or the return value of std::bind. Tasks can add other tasks, enabling the composition of an arbitrary number of tasks to obtain a final result.

Overloads of TaskManager::make_task_result(), TaskManager::make_task_when() and TaskManager::make_task_when_full() (but not TaskManager::make_task_compose()) also exist which take a function pointer (or an object reference and member function pointer) to a function which returns a value, with bound arguments, but these are deprecated in the 2.2 series of the library as they offer little advantage over using std::bind. (Although deprecated, there is no plan to remove these functions as they are there and they work - the deprecation is in effect guidance.) These deprecated functions can take up to three bound arguments in the case of a non-static member function, and four bound arguments in the case of any other function. In the case of a non-static member function, the referenced object whose member function is to be called must remain in existence until the task has completed. The target function passed by pointer (or member function pointer) can take a reference to const argument, as a copy of the object to be passed to the argument is taken to avoid dangling references, but it cannot take a reference to non-const argument.

Copying of the return value of the target function or callable object represented by the task may take place when using TaskManager::make_task_result(), TaskManager::make_task_when(), TaskManager::make_task_when_full() and TaskManager::make_task_compose(). When a task completes, the return value will be stored, either in a Cgu::AsyncResult object (if TaskManager::make_task_result() is called) or for the purposes of executing the 'when' callback in a glib main loop (if TaskManager::make_task_when(), TaskManager::make_task_when_full() or TaskManager::make_task_compose() are called). This storage will therefore cause the return value type's assignment operator or copy constructor to be called once unless that type has a move assignment operator or move constructor, in which case a move operation will be made where possible. Note that a 'when' callback takes the stored return value by reference to const and so without any additional copying upon the 'when' callback being executed in the main loop.

TaskManager objects do not provide thread cancellation. Thread cancellation is incompatible with the task-centred thread pool model. If task cancellation is wanted, use a Cgu::Thread::Future (or Cgu::Thread::Thread or Cgu::Thread::JoinableHandle) object instead, and have a dedicated thread for the cancelable task.

If glib < 2.32 is installed, g_thread_init() must be called before any TaskManager objects are constructed, which in turn means that with glib < 2.32 TaskManager objects may not be constructed as static objects in global namespace (that is, before g_thread_init() has been called in the program).

Any exceptions which propagate from a task will be consumed to protect the TaskManager object, and to detect whether this has happened there is a version of the TaskManager::add_task() method which takes a second argument comprising a 'fail' callback. If an exception propagates from the 'fail' callback that is also consumed and a g_critical() message issued. TaskManager::make_task_when_full() also provides for a 'fail' callback.

Tasks can be aborted by throwing Cgu::Thread::Exit (as well as any other exception). Where a task is managed by a TaskManager object, throwing Cgu::Thread::Exit will only terminate the task and not the thread on which it is running (and will cause the 'fail' callback to be executed, if there is one).

Any 'fail' callback passed to TaskManager::add_task() or TaskManager::make_task_when_full() must be fully bound. Whilst a task can pass error status to the 'fail' callback via shared data bound to both the task and the 'fail' callback (held by, say, a SharedLockPtr object), or a global error stack, 'fail' callbacks are generally best reserved for use with entirely unexpected exceptions, where the most reasonable course is to perform some orderly logging and shutdown. For handlable exceptions, in an asynchronous environment the best course is often to catch them and deal with them in the task itself and (where TaskManager::make_task_when_full(), TaskManager::make_task_when() or TaskManager::make_task_compose() is employed) return a value of the task function's return type indicating no result.

TaskManager objects have no copy constructor or copy assignment operator, as copying them would have no obvious semantic meaning. Whilst swapping or moving TaskManager objects would be meaningful, this is not implemented either because it would require an additional internal lock to be thread safe, and the circumstances in which moving or swapping would be useful are limited. Where a move option is wanted, a TaskManager object can be constructed on free store and held by std::unique_ptr.

Here is a compilable example of the calculator class referred to in the documentation on the AsyncResult but which uses a TaskManager object so that the calculator class can run more than one thread to service its calculations, using TaskManager::make_task_result():

#include <vector>
#include <numeric>
#include <ostream>
#include <iostream>
#include <glib.h>
#include <c++-gtk-utils/task_manager.h>
#include <c++-gtk-utils/async_result.h>
#include <c++-gtk-utils/shared_ptr.h>
using namespace Cgu;
class Calcs {
Thread::TaskManager tm;
public:
SharedLockPtr<AsyncResult<double>> mean(const std::vector<double>& nums) {
return tm.make_task_result([=]() -> double {
if (nums.empty()) return 0.0;
return std::accumulate(nums.begin(), nums.end(), 0.0)/nums.size();
});
}
// ... other calculation methods here
};
int main () {
g_thread_init(0);
Calcs calcs;
auto res1 = calcs.mean({1, 2, 8, 0});
auto res2 = calcs.mean({101, 53.7, 87, 1.2});
// ... do something else
std::cout << res1->get() << std::endl;
std::cout << res2->get() << std::endl;
}

Here is a reimplementation, using TaskManager::make_task_when(), of the example using a get_primes() function given in the documentation for Cgu::Thread::Future:

std::vector<long> get_primes(int n); // calculates the first n primes
// get the first 1,000 primes
using namespace Cgu;
Thread::TaskManager tm;
tm.make_task_when([] (const std::vector<long>& result) {
for (const auto& elt: result) {std::cout << elt << std::endl;}
},
0, // default main loop context
[] () {return get_primes(1,000);});

Where a task running on a TaskManager object is to block, the TaskManager::IncHandle scoped handle class can be used to increment the maximum number of threads running on the object's thread pool temporarily while blocking takes place, so as to enable another thread to keep a core active. This can be useful where a task is to 'join' on another task when composing tasks. Here is a compilable example:

#include <iostream>
#include <ostream>
#include <glib.h>
#include <c++-gtk-utils/task_manager.h>
using namespace Cgu;
// simulate a blocking operation, say from a server, with g_usleep()
int mult(int x, int y) {
g_usleep(100000);
return x * y;
}
int main(int argc, char* argv[]) {
g_thread_init(0);
Thread::TaskManager tm{1}; // only one core available unless blocking!
GMainLoop* loop = g_main_loop_new(0, true);
tm.make_task_when(
[loop] (const int& res) {
std::cout << res << std::endl;
g_main_loop_quit(loop);
},
0, // default main loop
[&tm] () -> int {
// this task multiplies 'a' by 2 and 'b' by 3, and adds the products
int a = 10;
int b = 12;
// start a sub-task
auto sub = tm.make_task_result([a, &tm] () -> int {
Thread::TaskManager::IncHandle h{tm};
return mult(a, 2);
});
// let the sub-task run; pretend that some other task in the
// program may also want to run while both this task and the
// sub-task block on mult(), so increment again
Thread::TaskManager::IncHandle h{tm};
// do blocking operations
return sub->get() + mult(b, 3);
}
);
g_main_loop_run(loop);
}

## Member Enumeration Documentation

enum Cgu::Thread::TaskManager::StopMode

Enumerator
wait_for_running |
wait_for_all |

## Constructor & Destructor Documentation

Cgu::Thread::TaskManager::TaskManager | ( | const TaskManager & | ) |  |
| delete

This class cannot be copied. The copy constructor is deleted.

Cgu::Thread::TaskManager::TaskManager | ( | unsigned int | max = `8`,
|  | unsigned int | min = `0`,
|  | unsigned int | idle = `10000`,
|  | bool | blocking = `true`,
|  | StopMode | mode = `TaskManager::wait_for_all`
| ) |  |

If the specified minimum number of threads is greater than 0, this constructor will start the required minimum number of threads. If glib < 2.32 is installed, g_thread_init() must be called before any TaskManager objects are constructed

Parameters

  max | The maximum number of threads which the TaskManager object will run in the thread pool. If the value passed as this argument is less than the value passed as 'min', the maximum number of threads will be set to 'min'. A value of 0 is not valid, and if this is passed the number will be set to the greater of 1 and 'min'.
  min | The minimum number of threads which the TaskManager object will run in the thread pool.
  idle | The length of time in milliseconds that threads greater in number than 'min' and not executing any tasks will remain in existence. The default is 10000 (10 seconds).
  blocking | If true, calls to stop_all() and the destructor will not return until the tasks remaining to be executed have finished (what is meant by "the tasks remaining to be executed" depends on the StopMode setting, for which see the documentation on the stop_all() method). If false, stop_all() and the destructor will return straight away (which in terms of the TaskManager class implementation is safe for the reasons explained in the documentation on the destructor).
  mode | The StopMode setting (either Cgu::Thread::TaskManager::wait_for_running or Cgu::Thread::TaskManager::wait_for_all) executed when running stop_all() or when the destructor is called. See the documentation on stop_all() for an explanation of the setting.

Exceptions

  std::bad_alloc | This exception might be thrown if memory is exhausted and the system throws in that case.
  Cgu::Thread::TaskError | This exception will be thrown if starting the specified minimum number of threads fails.
  Cgu::Thread::MutexError | This exception might be thrown if initialisation of the contained mutex fails. (It is often not worth checking for this, as it means either memory is exhausted or pthread has run out of other resources to create new mutexes.)
  Cgu::Thread::CondError | This exception might be thrown if initialisation of the contained condition variable fails. (It is often not worth checking for this, as it means either memory is exhausted or pthread has run out of other resources to create new condition variables.)

Since 2.0.12

Cgu::Thread::TaskManager::~TaskManager | ( | ) |  |

The destructor will call stop_all(), unless that method has previously been called explicitly without throwing std::bad_alloc. If the blocking setting is true, the destructor will not return until the tasks remaining to be executed have finished (what is meant by "the tasks remaining to be executed" depends on the StopMode setting, for which see the documentation on the stop_all() method.) If the blocking setting is false, the destructor will return straight away: this is safe, because TaskManager's internals for running tasks have been implemented using reference counting and will not be deleted until all threads running on the TaskManager object have finished, although the remaining tasks should not attempt to call any of TaskManager's methods once the TaskManager object itself has been destroyed.

The destructor is thread safe (any thread can destroy a TaskManager object) unless the blocking setting is true, in which case no task running on the TaskManager object may destroy the TaskManager object. Subject to that, it is not an error for a thread to destroy a TaskManager object and so invoke this destructor while another thread is already blocking in (if the blocking setting is true) or already out of (if the blocking setting is false) a call to stop_all() and remaining tasks are executing: if blocking, both calls (to stop_all() and to this destructor) would safely block together. Any given thread can similarly safely follow a non-blocking call to stop_all() by a non-blocking call to this destructor even though remaining tasks are executing. However, it is an error for a thread to call stop_all() after another thread has begun destruction of the TaskManager object (that is, after this destructor has been entered): there would then be an unresolvable race with the destructor.

The destructor will not throw.

If stop_all() has not previously been called explicitly and throws std::bad_alloc() when called in this destructor, the exception will be caught and consumed, but then the destructor will not block even if the blocking setting is true, and if the minimum number of threads is not 0 some threads might remain running during the entire program duration (albeit safely). Where the throwing of std::bad_alloc is a meaningful event (usually it isn't) and needs to be guarded against, call stop_all() explicitly before this destructor is entered, or use a minimum thread value of 0 and allow for the case of the destructor not blocking.

Since 2.0.12

## Member Function Documentation

void Cgu::Thread::TaskManager::add_task | ( | const Callback::Callback * | task) |  |
| inline

This method adds a new task. If one or more threads in the pool are currently blocking and waiting for a task, then the task will begin executing immediately in one of the threads. If not, and the value returned by get_used_threads() is less than the value returned by get_max_threads(), a new thread will start and the task will execute immediately in the new thread. Otherwise, the task will be queued for execution as soon as a thread becomes available. Tasks will be executed in the order in which they are added to the ThreadManager object. This method is thread safe (any thread may call it, including any task running on the TaskManager object).

A task may terminate itself prematurely by throwing Cgu::Thread::Exit. In addition, the implementation of TaskManager will consume any other exception escaping from the task callback and safely terminate the task concerned in order to protect the integrity of the TaskManager object. Where detecting any of these outcomes is important (usually it won't be), the two argument version of this method is available so that a 'fail' callback can be executed in these circumstances.

Parameters

  task | A callback representing the new task, as constructed by the Callback::lambda(), Callback::make() or Callback::make_ref() factory functions. Ownership is taken of this callback, and it will be disposed of when it has been finished with. If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued. The destructors of any bound arguments in the callback must not throw.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start and the 'task' callback will be disposed of.
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start and the 'task' callback will be disposed of.

Since 2.0.12

void Cgu::Thread::TaskManager::add_task | ( | std::unique_ptr< const Callback::Callback > | task,
|  | std::unique_ptr< const Callback::Callback > | fail
| ) |  |

This method adds a new task. If one or more threads in the pool are currently blocking and waiting for a task, then the task will begin executing immediately in one of the threads. If not, and the value returned by get_used_threads() is less than the value returned by get_max_threads(), a new thread will start and the task will execute immediately in the new thread. Otherwise, the task will be queued for execution as soon as a thread becomes available. Tasks will be executed in the order in which they are added to the ThreadManager object. This method is thread safe (any thread may call it, including any task running on the TaskManager object).

A task may terminate itself prematurely by throwing Cgu::Thread::Exit. In addition, the implementation of TaskManager will consume any other exception escaping from the task callback and safely terminate the task concerned in order to protect the integrity of the TaskManager object. Where detecting any of these outcomes is important (usually it won't be), a callback can be passed to the 'fail' argument which will execute if, and only if, either Cgu::Thread::Exit is thrown or some other exception has propagated from the task. This 'fail' callback is different from the 'fail' callback of Cgu::Thread::Future objects (programming for many tasks to a lesser number of threads requires different approaches from programming for one thread per task), and it executes in the task thread rather than executing in a glib main loop (however, the 'fail' callback can of course call Cgu::Callback::post() to execute another callback in a main loop, if that is what is wanted).

Parameters

  task | A callback representing the new task, as constructed by the Callback::lambda(), Callback::make() or Callback::make_ref() factory functions. If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.
  fail | A callback (as constructed by the Callback::lambda(), Callback::make() or Callback::make_ref() factory functions) which will be executed if the function or callable object executed by the 'task' callback exits by throwing Thread::Exit or some other exception. If an exception propagates from the 'fail' callback, this will be consumed to protect the TaskManager object, and a g_critical() warning will be issued.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'fail' callback will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'fail' callback will not execute).

Since 2.0.12

template<class Task , class = typename std::enable_if<!std::is_convertible<typename std::remove_reference<Task>::type, const Callback::Callback*>::value>::type>

void Cgu::Thread::TaskManager::add_task | ( | Task && | task) |  |
| inline

This method adds a new task. If one or more threads in the pool are currently blocking and waiting for a task, then the task will begin executing immediately in one of the threads. If not, and the value returned by get_used_threads() is less than the value returned by get_max_threads(), a new thread will start and the task will execute immediately in the new thread. Otherwise, the task will be queued for execution as soon as a thread becomes available. Tasks will be executed in the order in which they are added to the ThreadManager object. This method is thread safe (any thread may call it, including any task running on the TaskManager object).

A task may terminate itself prematurely by throwing Cgu::Thread::Exit. In addition, the implementation of TaskManager will consume any other exception escaping from the task callback and safely terminate the task concerned in order to protect the integrity of the TaskManager object. Where detecting any of these outcomes is important (usually it won't be), the two argument version of this method is available so that a 'fail' callback can be executed in these circumstances.

Parameters

  task | A callable object representing the new task, such as formed by a lambda expression or the result of std::bind. It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued. The destructors of any bound values must not throw.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start.
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start.

Note
  An exception might also be thrown if the copy or move constructor of the callable object throws. If such an exception is thrown, the task will not start.

Since 2.1.0

template<class Task , class Fail , class = typename std::enable_if<!std::is_convertible<Task, std::unique_ptr<const Callback::Callback>>::value && !std::is_convertible<Fail, std::unique_ptr<const Callback::Callback>>::value>::type>

void Cgu::Thread::TaskManager::add_task | ( | Task && | task,
|  | Fail && | fail
| ) |  |
| inline

This method adds a new task. If one or more threads in the pool are currently blocking and waiting for a task, then the task will begin executing immediately in one of the threads. If not, and the value returned by get_used_threads() is less than the value returned by get_max_threads(), a new thread will start and the task will execute immediately in the new thread. Otherwise, the task will be queued for execution as soon as a thread becomes available. Tasks will be executed in the order in which they are added to the ThreadManager object. This method is thread safe (any thread may call it, including any task running on the TaskManager object).

A task may terminate itself prematurely by throwing Cgu::Thread::Exit. In addition, the implementation of TaskManager will consume any other exception escaping from the task callback and safely terminate the task concerned in order to protect the integrity of the TaskManager object. Where detecting any of these outcomes is important (usually it won't be), a callback can be passed to the 'fail' argument which will execute if, and only if, either Cgu::Thread::Exit is thrown or some other exception has propagated from the task. This 'fail' callback is different from the 'fail' callback of Cgu::Thread::Future objects (programming for many tasks to a lesser number of threads requires different approaches from programming for one thread per task), and it executes in the task thread rather than executing in a glib main loop (however, the 'fail' callback can of course call Cgu::Callback::post() to execute another callback in a main loop, if that is what is wanted).

Parameters

  task | A callable object representing the new task, such as formed by a lambda expression or the result of std::bind. It must be fully bound (that is, it must take no arguments when called). The destructors of any bound values must not throw. If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.
  fail | A callable object (such as formed by a lambda expression or the result of std::bind) which will be executed if the callable object executed by the 'task' callback exits by throwing Thread::Exit or some other exception. It must be fully bound (that is, it must take no arguments when called). The destructors of any bound values must not throw. If an exception propagates from the 'fail' callback, this will be consumed to protect the TaskManager object, and a g_critical() warning will be issued.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'fail' callback will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'fail' callback will not execute).

Note
  An exception might also be thrown if the copy or move constructor of the 'task' or 'fail' callable objects throws. If such an exception is thrown, the task will not start (which also means that the 'fail' callback will not execute)

Since 2.1.0

void Cgu::Thread::TaskManager::change_max_threads | ( | int | delta) |  |

This will increase, or if 'delta' is negative reduce, the maximum number of threads which the TaskManager object will currently run in the thread pool by the value of 'delta'. The purpose of this is to enable a task to increment the maximum thread number where it is about to enter a call which may block for some time, with a view to decrementing it later when it has finished making blocking calls, so as to enable another thread to keep a core active. If 'delta' is negative and results in a max_threads value of less than the current number of running threads, the number of threads actually running will only be reduced as tasks complete, or as idle timeouts expire. This method does nothing if stop_all() has previously been called. This method is thread safe. Since version 2.2.1, the scoped handle class TaskManager::IncHandle is available which calls this method.

Parameters

  delta | The change (positive or negative) to the maximum number of threads which the TaskManager object will currently run in the thread pool. This method will not set the maximum value of threads to a value less than that returned by get_min_threads(), nor to a value less than 1.

Exceptions

  std::bad_alloc | If this call is passed a positive value and tasks are currently queued for execution, a new thread or threads will be started for the queued tasks, so this exception may be thrown on starting a new thread if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion).
  Cgu::Thread::TaskError | If this call is passed a positive value and tasks are currently queued for execution, a new thread or threads will be started for the queued tasks, so this exception may be thrown on starting a new thread if it fails to start correctly (this would mean that memory is exhausted, the pthread thread limit has been reached or pthread has run out of other resources to start new threads).

Since 2.0.14

bool Cgu::Thread::TaskManager::get_blocking | ( | ) |  | const

Gets the current blocking setting, which determines whether calls to stop_all() and the destructor will block waiting for all remaining tasks to complete. This value is established initially by the 'blocking' argument passed to the TaskManager constructor and can subequently be changed by calling set_blocking(). This method will not throw and is thread safe.

Returns
  The current blocking setting.

Since 2.0.12

unsigned int Cgu::Thread::TaskManager::get_idle_time | ( | ) |  | const

Gets the length of time in milliseconds that threads greater in number than the minimum and not executing any tasks will remain in existence waiting for new tasks. This value is established initially by the 'idle' argument passed to the TaskManager constructor and can subequently be changed by calling set_idle_time(). The default value is 10000 (10 seconds). This method will not throw and is thread safe.

Returns
  The idle time in milliseconds.

Since 2.0.12

unsigned int Cgu::Thread::TaskManager::get_max_threads | ( | ) |  | const

Gets the maximum number of threads which the TaskManager object is currently set to run in the thread pool. This value is established initially by the 'max' argument passed to the TaskManager constructor and can subequently be changed by calling set_max_threads() or change_max_threads(). The default value is

1. This method will not throw and is thread safe. However, if a blocking task might use the TaskManager::IncHandle class (or increase and then decrease the number by hand by calling change_max_threads()), this method will not usually be of any particular value.
   Returns
     The maximum number of threads.
   Since 2.0.12

unsigned int Cgu::Thread::TaskManager::get_min_threads | ( | ) |  | const

Gets the minimum number of threads which the TaskManager object will run in the thread pool (these threads will last until stop_all() is called or the TaskManager object is destroyed). This value is established by the 'min' argument passed to the TaskManager constructor and cannot subequently be changed. The default is 0. This method will not throw and is thread safe.

Returns
  The minimum number of threads.

Since 2.0.12

StopMode Cgu::Thread::TaskManager::get_stop_mode | ( | ) |  | const

Gets the current StopMode setting (either Cgu::Thread::TaskManager::wait_for_running or Cgu::Thread::TaskManager::wait_for_all) executed when running stop_all() or when the destructor is called. See the documentation on stop_all() for an explanation of the setting. This value is established initially by the 'mode' argument passed to the TaskManager constructor and can subequently be changed by calling set_stop_mode(). This method will not throw and is thread safe.

Returns
  The current StopMode setting.

Since 2.0.12

unsigned int Cgu::Thread::TaskManager::get_tasks | ( | ) |  | const

Gets the number of tasks which the TaskManager object is at present either running in the thread pool or has queued for execution. This value will be less than the number returned by get_used_threads() if threads in the thread pool are currently waiting to receive tasks for execution. This method will not throw and is thread safe.

Returns
  The number of tasks either running or queued for execution.

Since 2.0.12

unsigned int Cgu::Thread::TaskManager::get_used_threads | ( | ) |  | const

Gets the number of threads which the TaskManager object is currently running in the thread pool, including those blocking waiting for a task. This value could be greater than the number returned by get_max_threads() if set_max_threads() has recently been called with a value which is less than that number but not enough tasks have since completed to reduce the number of running threads to the new value set. This method will not throw and is thread safe.

Returns
  The number of threads running in the thread pool, including those blocking waiting for a task.

Since 2.0.12

bool Cgu::Thread::TaskManager::is_error | ( | ) |  | const

This will return true if a thread required by the thread pool has failed to start correctly because of memory exhaustion or because pthread has run out of other resources to start new threads, or because an internal operation has thrown std::bad_alloc. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, and even more so where glib is used, as that terminates a program if memory cannot be obtained from the operating system, but there may be some specialized cases where the return value of this method is useful - this class does not use any glib functions which might cause such termination.) This method will not throw and is thread safe.

Since 2.0.12

template<class Ret , class Func >

void Cgu::Thread::TaskManager::make_task_compose | ( | Func && | f,
|  | GMainContext * | context,
|  | std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> | when
| ) |  |
| inline

This is an abbreviated version of make_task_when_full(), which is for use when it is known that the callable object passed to this method does not throw, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

This method does the same as the version of make_task_when() taking a callable object, except that this method takes that object as its first argument and the 'when' callback as its last argument in order to aid task composition, and in particular so tasks compose in user code in a visually ordered manner.

More particularly, like make_task_when_full(), this method is a wrapper which will take a callable object which returns a value, and constructs a TaskManager task which will execute that object by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the callable object's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

Parameters

  f | The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void). It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.
  context | The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  when | A callback which will be executed if and when the callable object passed to this method finishes correctly. The callback is passed that object's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note
  1. This method will also throw if the copy or move constructor of the callable object throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  2. If the callable object passed as an argument has both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.

Since 2.0.14

template<class Func , class When , class = typename std::enable_if<!std::is_convertible<When, std::unique_ptr<const Callback::CallbackArg<const typename std::result_of<Func()>::type&>>>::value>::type>

void Cgu::Thread::TaskManager::make_task_compose | ( | Func && | func,
|  | GMainContext * | context,
|  | When && | when
| ) |  |
| inline

This is an abbreviated version of make_task_when_full(), which is for use when it is known that the callable object passed to the 'func' argument of this method does not throw, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

This method does the same as make_task_when(), except that this method takes the callable object to be executed as a task as its first argument and the 'when' callback as its last argument in order to aid task composition, and in particular so tasks compose in user code in a visually ordered manner.

More particularly, like make_task_when_full(), this method is a wrapper which takes a callable object which returns a value as its 'func' argument, and constructs a TaskManager task which will execute that object by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the return value of the 'func' argument when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

Parameters

  func | The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void). It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.
  context | The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  when | A callable object (such as formed by a lambda expression or the result of std::bind) which will be executed if and when the 'func' object passed to this method finishes correctly. The 'when' callback is passed that objects's return value when invoked, and should take a single unbound argument, namely a reference to const of the type of that return value. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note
  1. This method will also throw if the copy or move constructor of the 'func' or 'when' callable objects throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  2. If any of the callable objects passed to this method have both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.

Since 2.1.0

template<class Ret , class... Params, class... Args, class T >

Cgu::SharedLockPtr<Cgu::AsyncResult<Ret> > Cgu::Thread::TaskManager::make_task_result | ( | T & | t,
|  | Ret(T::*)(Params...) | func,
|  | Args &&... | args
| ) |  |

Deprecated:

DEPRECATED. Use the versions of make_task_result() which take callable objects.

This is a wrapper which will take a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and returns a Cgu::AsyncResult object (held by Cgu::SharedLockPtr) which will provide the value that the function returns. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

This method can take up to three bound arguments for the target member function.

If the function passed to this method exits by throwing Thread::Exit or some other exception, then the exception will be consumed and the returned Cgu::AsyncResult object's get() method will unblock and its get_error() method will return -1.

Parameters

  t | The object whose member function passed to this method is to execute as a task.
  func | The member function to be executed as a task.
  args | The arguments to be passed to that member function.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start.
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start.

Note
  This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start.

Since 2.0.13

template<class Ret , class... Params, class... Args, class T >

Cgu::SharedLockPtr<Cgu::AsyncResult<Ret> > Cgu::Thread::TaskManager::make_task_result | ( | const T & | t,
|  | Ret(T::*)(Params...) const | func,
|  | Args &&... | args
| ) |  |

Deprecated:

DEPRECATED. Use the versions of make_task_result() which take callable objects.

This is a wrapper which will take a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and returns a Cgu::AsyncResult object (held by Cgu::SharedLockPtr) which will provide the value that the function returns. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

This method can take up to three bound arguments for the target member function.

If the function passed to this method exits by throwing Thread::Exit or some other exception, then the exception will be consumed and the returned Cgu::AsyncResult object's get() method will unblock and its get_error() method will return -1.

Parameters

  t | The object whose member function passed to this method is to execute as a task.
  func | The member function to be executed as a task.
  args | The arguments to be passed to that member function.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start.
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start.

Note
  This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start.

Since 2.0.13

template<class Ret , class... Params, class... Args>

Cgu::SharedLockPtr<Cgu::AsyncResult<Ret> > Cgu::Thread::TaskManager::make_task_result | ( | Ret(*)(Params...) | func,
|  | Args &&... | args
| ) |  |

Deprecated:

DEPRECATED. Use the versions of make_task_result() which take callable objects.

This is a wrapper which will take a pointer to a function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and returns a Cgu::AsyncResult object (held by Cgu::SharedLockPtr) which will provide the value that the function returns. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

This method can take up to four bound arguments for the target function.

If the function passed to this method exits by throwing Thread::Exit or some other exception, then the exception will be consumed and the returned Cgu::AsyncResult object's get() method will unblock and its get_error() method will return -1.

Parameters

  func | The function to be executed as a task.
  args | The arguments to be passed to that function.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start.
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start.

Note
  This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start.

Since 2.0.13

template<class Ret , class Func >

Cgu::SharedLockPtr<Cgu::AsyncResult<Ret> > Cgu::Thread::TaskManager::make_task_result | ( | Func && | f) |  |

This is a wrapper which will take a callable object (such as a std::function object, a lambda or the return value of std::bind) representing a function which returns a value, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and returns a Cgu::AsyncResult object (held by Cgu::SharedLockPtr) which will provide the value that the function returns. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

If the callable object passed to this method exits by throwing Thread::Exit or some other exception, then the exception will be consumed and the returned Cgu::AsyncResult object's get() method will unblock and its get_error() method will return -1.

Parameters

  f | The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void).

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start.
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start.

Note
  1. This method will also throw if the copy or move constructor of the callable object throws. If such an exception is thrown, the task will not start.
  2. If the callable object passed as an argument has both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.

Since 2.0.14

template<class Ret , class... Params, class... Args, class T >

void Cgu::Thread::TaskManager::make_task_when | ( | std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> | when,
|  | GMainContext * | context,
|  | T & | t,
|  | Ret(T::*)(Params...) | func,
|  | Args &&... | args
| ) |  |
| inline

Deprecated:

DEPRECATED. Use the versions of make_task_when() which take callable objects.

This is an abbreviated version of make_task_when_full(), which is for use when it is known that the member function passed to this method, and the copy constructors of any non-reference bound arguments passed to it, do not throw, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

This method can take up to three bound arguments for the target member function.

Like make_task_when_full(), this method is a wrapper which will take a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the member function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

Parameters

  when | A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  context | The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  t | The object whose member function passed to this method is to execute as a task.
  func | The member function to be executed as a task. If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.
  args | The arguments to be passed to that member function.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note
  This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Since 2.0.13

template<class Ret , class... Params, class... Args, class T >

void Cgu::Thread::TaskManager::make_task_when | ( | std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> | when,
|  | GMainContext * | context,
|  | const T & | t,
|  | Ret(T::*)(Params...) const | func,
|  | Args &&... | args
| ) |  |
| inline

Deprecated:

DEPRECATED. Use the versions of make_task_when() which take callable objects.

This is an abbreviated version of make_task_when_full(), which is for use when it is known that the member function passed to this method, and the copy constructors of any non-reference bound arguments passed to it, do not throw, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

This method can take up to three bound arguments for the target member function.

Like make_task_when_full(), this method is a wrapper which will take a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the member function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

Parameters

  when | A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  context | The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  t | The object whose member function passed to this method is to execute as a task.
  func | The member function to be executed as a task. If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.
  args | The arguments to be passed to that member function.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note
  This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Since 2.0.13

template<class Ret , class... Params, class... Args>

void Cgu::Thread::TaskManager::make_task_when | ( | std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> | when,
|  | GMainContext * | context,
|  | Ret(*)(Params...) | func,
|  | Args &&... | args
| ) |  |
| inline

Deprecated:

DEPRECATED. Use the versions of make_task_when() which take callable objects.

This is an abbreviated version of make_task_when_full(), which is for use when it is known that the function passed to this method, and the copy constructors of any non-reference bound arguments passed to it, do not throw, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

This method can take up to four bound arguments for the target function.

Like make_task_when_full(), this method is a wrapper which will take a pointer to a function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

Parameters

  when | A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  context | The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  func | The function to be executed as a task. If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.
  args | The arguments to be passed to that function.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note
  This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Since 2.0.13

template<class Ret , class Func >

void Cgu::Thread::TaskManager::make_task_when | ( | std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> | when,
|  | GMainContext * | context,
|  | Func && | f
| ) |  |
| inline

This is an abbreviated version of make_task_when_full(), which is for use when it is known that the callable object passed to this method does not throw, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

Like make_task_when_full(), this method is a wrapper which will take a callable object which returns a value, and constructs a TaskManager task which will execute that object by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the callable object's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

There is a similar make_task_compose() function which has the callable object to be executed as a task as its first argument and the 'when' callback as its last argument, in order to aid task composition.

Parameters

  when | A callback which will be executed if and when the callable object passed to this method finishes correctly. The callback is passed that object's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  context | The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  f | The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void). It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note
  1. This method will also throw if the copy or move constructor of the callable object throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  2. If the callable object passed as an argument has both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.

Since 2.0.14

template<class When , class Func , class = typename std::enable_if<!std::is_convertible<When, std::unique_ptr<const Callback::CallbackArg<const typename std::result_of<Func()>::type&>>>::value>::type>

void Cgu::Thread::TaskManager::make_task_when | ( | When && | when,
|  | GMainContext * | context,
|  | Func && | func
| ) |  |
| inline

This is an abbreviated version of make_task_when_full(), which is for use when it is known that the callable object passed to the 'func' argument of this method does not throw, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

Like make_task_when_full(), this method is a wrapper which takes a callable object which returns a value as its 'func' argument, and constructs a TaskManager task which will execute that object by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the return value of the 'func' argument when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

There is a similar make_task_compose() function which has the callable object to be executed as a task as its first argument and the 'when' callback as its last argument, in order to aid task composition.

Parameters

  when | A callable object (such as formed by a lambda expression or the result of std::bind) which will be executed if and when the 'func' object passed to this method finishes correctly. The 'when' callback is passed that objects's return value when invoked, and should take a single unbound argument, namely a reference to const of the type of that return value. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  context | The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  func | The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void). It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note
  1. This method will also throw if the copy or move constructor of the 'func' or 'when' callable objects throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).
  2. If any of the callable objects passed to this method have both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.

Since 2.1.0

template<class Ret , class... Params, class... Args, class T >

void Cgu::Thread::TaskManager::make_task_when_full | ( | std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> | when,
|  | Cgu::Releaser * | when_releaser,
|  | std::unique_ptr< const Cgu::Callback::Callback > | fail,
|  | Cgu::Releaser * | fail_releaser,
|  | gint | priority,
|  | GMainContext * | context,
|  | T & | t,
|  | Ret(T::*)(Params...) | func,
|  | Args &&... | args
| ) |  |

Deprecated:

DEPRECATED. Use the versions of make_task_when_full() which take callable objects.

This is a wrapper which will take a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the member function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

This method can take up to three bound arguments for the target member function.

Note that unlike add_task(), but like the 'fail' callback of Cgu::Thread::Future objects, if a fail callback is provided to this method and it executes, it will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Note also that if releasers are provided for the 'when' or 'fail' callbacks, these are passed by pointer and not by reference (this is so that a NULL pointer can indicate that no releaser is to be provided). If provided, a releaser will enable automatic disconnection of the 'when' or 'fail' callback, if the object having the callback function as a member is destroyed. For this to be race free, the lifetime of that object must be controlled by the thread in whose main loop the 'when' or 'fail' callback will execute.

The make_task_when() method is similar to this method but provides an abbreviated set of paramaters suitable for most cases. This method is for use where releasers or a 'fail' callback are required.

Parameters

  when | A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  when_releaser | A pointer to a Releaser object for automatic disconnection of the 'when' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  fail | A callback which will be executed if the 'when' callback does not execute. This would happen if the function passed to this method exits by throwing Thread::Exit or some other exception or the copy constructor of a non-reference argument of that function throws, or if the 'when' callback does not execute because the internal implementation of this wrapper throws std::bad_alloc (which will not happen if the library has been installed using the –with-glib-memory-slices-no-compat configuration option: instead glib will terminate the program if it is unable to obtain memory from the operating system). If an exception propagates from the 'fail' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method. An empty std::unique_ptr object indicates no 'fail' callback.
  fail_releaser | A pointer to a Releaser object for automatic disconnection of the 'fail' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  priority | The priority to be given in the main loop to the 'when' callback or any 'fail' callback. In ascending order of priorities, priorities are G_PRIORITY_LOW, G_PRIORITY_DEFAULT_IDLE, G_PRIORITY_HIGH_IDLE, G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. This determines the order in which the callback will appear in the event list in the main loop, not the priority which the OS will adopt.
  context | The glib main context of the main loop in which the 'when' callback or any 'fail' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  t | The object whose member function passed to this method is to execute as a task.
  func | The member function to be executed as a task. If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.
  args | The arguments to be passed to that member function.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Note
  1. This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  2. If a 'when_releaser' or a 'fail_releaser' argument is provided, it is in theory possible (if memory is exhausted and the system throws in that case) that an internal SafeEmitterArg object will throw std::bad_alloc when emitting/executing the 'when' or 'fail' callback in the glib main loop, with the result that the relevant callback will not execute (instead the exception will be consumed and a g_critical() warning will be issued). This is rarely of any relevance because glib will abort the program if it is itself unable to obtain memory from the operating system. However, where it is relevant, design the program so that it is not necessary to provide a releaser object.

Since 2.0.13

template<class Ret , class... Params, class... Args, class T >

void Cgu::Thread::TaskManager::make_task_when_full | ( | std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> | when,
|  | Cgu::Releaser * | when_releaser,
|  | std::unique_ptr< const Cgu::Callback::Callback > | fail,
|  | Cgu::Releaser * | fail_releaser,
|  | gint | priority,
|  | GMainContext * | context,
|  | const T & | t,
|  | Ret(T::*)(Params...) const | func,
|  | Args &&... | args
| ) |  |

Deprecated:

DEPRECATED. Use the versions of make_task_when_full() which take callable objects.

This is a wrapper which will take a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the member function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

This method can take up to three bound arguments for the target member function.

Note that unlike add_task(), but like the 'fail' callback of Cgu::Thread::Future objects, if a fail callback is provided to this method and it executes, it will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Note also that if releasers are provided for the 'when' or 'fail' callbacks, these are passed by pointer and not by reference (this is so that a NULL pointer can indicate that no releaser is to be provided). If provided, a releaser will enable automatic disconnection of the 'when' or 'fail' callback, if the object having the callback function as a member is destroyed. For this to be race free, the lifetime of that object must be controlled by the thread in whose main loop the 'when' or 'fail' callback will execute.

The make_task_when() method is similar to this method but provides an abbreviated set of paramaters suitable for most cases. This method is for use where releasers or a 'fail' callback are required.

Parameters

  when | A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  when_releaser | A pointer to a Releaser object for automatic disconnection of the 'when' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  fail | A callback which will be executed if the 'when' callback does not execute. This would happen if the function passed to this method exits by throwing Thread::Exit or some other exception or the copy constructor of a non-reference argument of that function throws, or if the 'when' callback does not execute because the internal implementation of this wrapper throws std::bad_alloc (which will not happen if the library has been installed using the –with-glib-memory-slices-no-compat configuration option: instead glib will terminate the program if it is unable to obtain memory from the operating system). If an exception propagates from the 'fail' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method. An empty std::unique_ptr object indicates no 'fail' callback.
  fail_releaser | A pointer to a Releaser object for automatic disconnection of the 'fail' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  priority | The priority to be given in the main loop to the 'when' callback or any 'fail' callback. In ascending order of priorities, priorities are G_PRIORITY_LOW, G_PRIORITY_DEFAULT_IDLE, G_PRIORITY_HIGH_IDLE, G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. This determines the order in which the callback will appear in the event list in the main loop, not the priority which the OS will adopt.
  context | The glib main context of the main loop in which the 'when' callback or any 'fail' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  t | The object whose member function passed to this method is to execute as a task.
  func | The member function to be executed as a task. If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.
  args | The arguments to be passed to that member function.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Note
  1. This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  2. If a 'when_releaser' or a 'fail_releaser' argument is provided, it is in theory possible (if memory is exhausted and the system throws in that case) that an internal SafeEmitterArg object will throw std::bad_alloc when emitting/executing the 'when' or 'fail' callback in the glib main loop, with the result that the relevant callback will not execute (instead the exception will be consumed and a g_critical() warning will be issued). This is rarely of any relevance because glib will abort the program if it is itself unable to obtain memory from the operating system. However, where it is relevant, design the program so that it is not necessary to provide a releaser object.

Since 2.0.13

template<class Ret , class... Params, class... Args>

void Cgu::Thread::TaskManager::make_task_when_full | ( | std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> | when,
|  | Cgu::Releaser * | when_releaser,
|  | std::unique_ptr< const Cgu::Callback::Callback > | fail,
|  | Cgu::Releaser * | fail_releaser,
|  | gint | priority,
|  | GMainContext * | context,
|  | Ret(*)(Params...) | func,
|  | Args &&... | args
| ) |  |

Deprecated:

DEPRECATED. Use the versions of make_task_when_full() which take callable objects.

This is a wrapper which will take a pointer to a function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

This method can take up to four bound arguments for the target function.

Note that unlike add_task(), but like the 'fail' callback of Cgu::Thread::Future objects, if a fail callback is provided to this method and it executes, it will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Note also that if releasers are provided for the 'when' or 'fail' callbacks, these are passed by pointer and not by reference (this is so that a NULL pointer can indicate that no releaser is to be provided). If provided, a releaser will enable automatic disconnection of the 'when' or 'fail' callback, if the object of which the releaser is a member is destroyed. For this to be race free, the lifetime of that object must be controlled by the thread in whose main loop the 'when' or 'fail' callback will execute.

The make_task_when() method is similar to this method but provides an abbreviated set of paramaters suitable for most cases. This method is for use where releasers or a 'fail' callback are required.

Parameters

  when | A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  when_releaser | A pointer to a Releaser object for automatic disconnection of the 'when' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  fail | A callback which will be executed if the 'when' callback does not execute. This would happen if the function passed to this method exits by throwing Thread::Exit or some other exception or the copy constructor of a non-reference argument of that function throws, or if the 'when' callback does not execute because the internal implementation of this wrapper throws std::bad_alloc (which will not happen if the library has been installed using the –with-glib-memory-slices-no-compat configuration option: instead glib will terminate the program if it is unable to obtain memory from the operating system). If an exception propagates from the 'fail' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method. An empty std::unique_ptr object indicates no 'fail' callback.
  fail_releaser | A pointer to a Releaser object for automatic disconnection of the 'fail' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  priority | The priority to be given in the main loop to the 'when' callback or any 'fail' callback. In ascending order of priorities, priorities are G_PRIORITY_LOW, G_PRIORITY_DEFAULT_IDLE, G_PRIORITY_HIGH_IDLE, G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. This determines the order in which the callback will appear in the event list in the main loop, not the priority which the OS will adopt.
  context | The glib main context of the main loop in which the 'when' callback or any 'fail' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  func | The function to be executed as a task. If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.
  args | The arguments to be passed to that function.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Note
  1. This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  2. If a 'when_releaser' or a 'fail_releaser' argument is provided, it is in theory possible (if memory is exhausted and the system throws in that case) that an internal SafeEmitterArg object will throw std::bad_alloc when emitting/executing the 'when' or 'fail' callback in the glib main loop, with the result that the relevant callback will not execute (instead the exception will be consumed and a g_critical() warning will be issued). This is rarely of any relevance because glib will abort the program if it is itself unable to obtain memory from the operating system. However, where it is relevant, design the program so that it is not necessary to provide a releaser object.

Since 2.0.13

template<class Ret , class Func >

void Cgu::Thread::TaskManager::make_task_when_full | ( | std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> | when,
|  | Cgu::Releaser * | when_releaser,
|  | std::unique_ptr< const Cgu::Callback::Callback > | fail,
|  | Cgu::Releaser * | fail_releaser,
|  | gint | priority,
|  | GMainContext * | context,
|  | Func && | func
| ) |  |

This is a wrapper which will take a callable object (such as a std::function object, a lambda or the return value of std::bind) representing a function which returns a value, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

Note that unlike add_task(), but like the 'fail' callback of Cgu::Thread::Future objects, if a fail callback is provided to this method and it executes, it will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Note also that if releasers are provided for the 'when' or 'fail' callbacks, these are passed by pointer and not by reference (this is so that a NULL pointer can indicate that no releaser is to be provided). If provided, a releaser will enable automatic disconnection of the 'when' or 'fail' callback, if the object of which the releaser is a member is destroyed. For this to be race free, the lifetime of that object must be controlled by the thread in whose main loop the 'when' or 'fail' callback will execute.

The make_task_when() method is similar to this method but provides an abbreviated set of parameters suitable for most cases. This method is for use where releasers or a 'fail' callback are required.

Parameters

  when | A callback which will be executed if and when the callable object passed as 'func' to this method finishes correctly. The callback is passed that object's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  when_releaser | A pointer to a Releaser object for automatic disconnection of the 'when' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  fail | A callback which will be executed if the 'when' callback does not execute. This would happen if the callable object passed as 'func' to this method exits by throwing Thread::Exit or some other exception (or if that object represents a function taking a non-reference argument whose copy constructor throws), or if the 'when' callback does not execute because the internal implementation of this wrapper throws std::bad_alloc (which will not happen if the library has been installed using the –with-glib-memory-slices-no-compat configuration option: instead glib will terminate the program if it is unable to obtain memory from the operating system). If an exception propagates from the 'fail' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method. An empty std::unique_ptr object indicates no 'fail' callback.
  fail_releaser | A pointer to a Releaser object for automatic disconnection of the 'fail' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  priority | The priority to be given in the main loop to the 'when' callback or any 'fail' callback. In ascending order of priorities, priorities are G_PRIORITY_LOW, G_PRIORITY_DEFAULT_IDLE, G_PRIORITY_HIGH_IDLE, G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. This determines the order in which the callback will appear in the event list in the main loop, not the priority which the OS will adopt.
  context | The glib main context of the main loop in which the 'when' callback or any 'fail' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  func | The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void). It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Note
  1. This method will also throw if the copy or move constructor of the callable object throws. If such an exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  2. If the callable object passed as an argument has both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.
  3. If a 'when_releaser' or a 'fail_releaser' argument is provided, it is in theory possible (if memory is exhausted and the system throws in that case) that an internal SafeEmitterArg object will throw std::bad_alloc when emitting/executing the 'when' or 'fail' callback in the glib main loop, with the result that the relevant callback will not execute (instead the exception will be consumed and a g_critical() warning will be issued). This is rarely of any relevance because glib will abort the program if it is itself unable to obtain memory from the operating system. However, where it is relevant, design the program so that it is not necessary to provide a releaser object.

Since 2.0.14

template<class When , class Fail , class Func , class = typename std::enable_if<!std::is_convertible<When, std::unique_ptr<const Callback::CallbackArg<const typename std::result_of<Func()>::type&>>>::value && !std::is_convertible<Fail, std::unique_ptr<const Callback::Callback>>::value>::type>

void Cgu::Thread::TaskManager::make_task_when_full | ( | When && | when,
|  | Cgu::Releaser * | when_releaser,
|  | Fail && | fail,
|  | Cgu::Releaser * | fail_releaser,
|  | gint | priority,
|  | GMainContext * | context,
|  | Func && | func
| ) |  |
| inline

This is a wrapper which will take a callable object (such as a std::function object, a lambda or the return value of std::bind) representing a function which returns a value, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

Note that unlike add_task(), but like the 'fail' callback of Cgu::Thread::Future objects, if a fail callback is provided to this method and it executes, it will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Note also that if releasers are provided for the 'when' or 'fail' callbacks, these are passed by pointer and not by reference (this is so that a NULL pointer can indicate that no releaser is to be provided). If provided, a releaser will enable automatic disconnection of the 'when' or 'fail' callback, if the object of which the releaser is a member is destroyed. For this to be race free, the lifetime of that object must be controlled by the thread in whose main loop the 'when' or 'fail' callback will execute.

The make_task_when() method is similar to this method but provides an abbreviated set of parameters suitable for most cases. This method is for use where releasers or a 'fail' callback are required.

Parameters

  when | A callable object (such as formed by a lambda expression or the result of std::bind) which will be executed if and when the 'func' object passed to this method finishes correctly. The 'when' callback is passed that objects's return value when invoked, and should take a single unbound argument, namely a reference to const of the type of that return value. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
  when_releaser | A pointer to a Releaser object for automatic disconnection of the 'when' callback before it executes in a main loop (mainly relevant if the callback calls a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  fail | A callable object (such as formed by a lambda expression or the result of std::bind) which will be executed if the 'when' callback does not execute. This would happen if the the callable object passed as 'func' to this method exits by throwing Thread::Exit or some other exception, or if the 'when' callback does not execute because the internal implementation of this wrapper throws std::bad_alloc (which will not happen if the library has been installed using the –with-glib-memory-slices-no-compat configuration option: instead glib will terminate the program if it is unable to obtain memory from the operating system). The callable object must be fully bound (that is, it must take no arguments when called). If an exception propagates from the 'fail' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method. If no 'fail' callback is wanted, pass a lambda which does nothing.
  fail_releaser | A pointer to a Releaser object for automatic disconnection of the 'fail' callback before it executes in a main loop (mainly relevant if the callback calls a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
  priority | The priority to be given in the main loop to the 'when' callback or any 'fail' callback. In ascending order of priorities, priorities are G_PRIORITY_LOW, G_PRIORITY_DEFAULT_IDLE, G_PRIORITY_HIGH_IDLE, G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. This determines the order in which the callback will appear in the event list in the main loop, not the priority which the OS will adopt.
  context | The glib main context of the main loop in which the 'when' callback or any 'fail' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
  func | The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void). It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the sytem throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called. It will also be thrown if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc, or a thread has failed to start correctly. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, but there may be some specialized cases where the return value of is_error() is useful.) If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Note
  1. This method will also throw if the copy or move constructor of the 'func', 'when' or 'fail' callable objects throws. If such an exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).
  2. If any of the callable objects passed to this method have both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.
  3. If a 'when_releaser' or a 'fail_releaser' argument is provided, it is in theory possible (if memory is exhausted and the system throws in that case) that an internal SafeEmitterArg object will throw std::bad_alloc when emitting/executing the 'when' or 'fail' callback in the glib main loop, with the result that the relevant callback will not execute (instead the exception will be consumed and a g_critical() warning will be issued). This is rarely of any relevance because glib will abort the program if it is itself unable to obtain memory from the operating system. However, where it is relevant, design the program so that it is not necessary to provide a releaser object.

Since 2.1.0

TaskManager& Cgu::Thread::TaskManager::operator= | ( | const TaskManager & | ) |  |
| delete

This class cannot be copied. The assignment operator is deleted.

void Cgu::Thread::TaskManager::set_blocking | ( | bool | blocking) |  |

Sets the current blocking setting, which determines whether calls to stop_all() and the destructor will block waiting for all remaining tasks to complete. This method cannot be called after stop_all() has been called (if that is attempted, Cgu::Thread::TaskError will be thrown). It is thread safe.

Parameters

  blocking | The new blocking setting.

Exceptions

  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called.

Since 2.0.12

void Cgu::Thread::TaskManager::set_idle_time | ( | unsigned int | idle) |  |

Sets the length of time in milliseconds that threads greater in number than the minimum and not executing any tasks will remain in existence waiting for new tasks. This will only have effect for threads in the pool which begin waiting for new tasks after this method is called. This method will not throw and is thread safe.

Parameters

  idle | The length of the idle time in milliseconds during which threads will remain waiting for new tasks.

Since 2.0.12

void Cgu::Thread::TaskManager::set_max_threads | ( | unsigned int | max) |  |

Deprecated:

DEPRECATED. Use change_max_threads() instead. This method will interfere with the intended operation of the ThreadManager::IncHandle class if one task constructs a IncHandle object and another calls this method.

Sets the maximum number of threads which the TaskManager object will currently run in the thread pool. If this is less than the current number of running threads, the number of threads actually running will only be reduced as tasks complete, or as idle timeouts expire. This method does nothing if stop_all() has previously been called. This method is thread safe.

Parameters

  max | The maximum number of threads which the TaskManager object will currently run in the thread pool. This method will not set the maximum value of threads to a value less than that returned by get_min_threads(), nor to a value less than 1.

Exceptions

  std::bad_alloc | If this call is passed a value for 'max' which increases the maximum number of threads from its previous setting and tasks are currently queued for execution, new threads will be started for the queued tasks, so this exception may be thrown on starting the new threads if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion).
  Cgu::Thread::TaskError | If this call is passed a value for 'max' which increases the maximum number of threads from its previous setting and tasks are currently queued for execution, new threads will be started for the queued tasks, so this exception may be thrown on starting the new threads if a thread fails to start correctly (this would mean that memory is exhausted, the pthread thread limit has been reached or pthread has run out of other resources to start new threads).

Since 2.0.12

void Cgu::Thread::TaskManager::set_stop_mode | ( | StopMode | mode) |  |

Sets the current StopMode setting (either Cgu::Thread::TaskManager::wait_for_running or Cgu::Thread::TaskManager::wait_for_all) executed when running stop_all() or when the destructor is called. See the documentation on stop_all() for an explanation of the setting. This method will not throw and is thread safe.

Parameters

  mode | The new StopMode setting.

Since 2.0.12

void Cgu::Thread::TaskManager::stop_all | ( | ) |  |

This will cause the TaskManager object to stop running tasks. The precise effect depends on the current StopMode and blocking settings. If StopMode is set to Cgu::Thread::TaskManager::wait_for_running, all queued tasks which are not yet running on a thread will be dispensed with, but any already running will be left to complete normally. If StopMode is set to Cgu::Thread::TaskManager::wait_for_all, both already running tasks and all tasks already queued will be permitted to execute and complete normally. If the blocking setting is set to true, this method will wait until all the tasks still to execute have finished before returning, and if false it will return straight away.

After this method has been called, any attempt to add further tasks with the add_task() method will fail, and add_task() will throw Cgu::Thread::TaskError.

This method is thread safe (any thread may call it) unless the blocking setting is true, in which case no task running on the TaskManager object may call this method.

Exceptions

  std::bad_alloc | This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion).
  Cgu::Thread::TaskError | This exception will be thrown if stop_all() has previously been called, unless that previous call threw std::bad_alloc: if std::bad_alloc is thrown, this method may be called again to stop all threads, once the memory deficiency is dealt with, but no other methods of the TaskManager object should be called.

Since 2.0.12

The documentation for this class was generated from the following file:

- task_manager.h