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thread.h
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1 /* Copyright (C) 2005 to 2013 Chris Vine
2
3 The library comprised in this file or of which this file is part is
4 distributed by Chris Vine under the GNU Lesser General Public
5 License as follows:
6
7 This library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public License
9 as published by the Free Software Foundation; either version 2.1 of
10 the License, or (at your option) any later version.
11
12 This library is distributed in the hope that it will be useful, but
13 WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License, version 2.1, for more details.
16
17 You should have received a copy of the GNU Lesser General Public
18 License, version 2.1, along with this library (see the file LGPL.TXT
19 which came with this source code package in the c++-gtk-utils
20 sub-directory); if not, write to the Free Software Foundation, Inc.,
21 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
22
23 */
24
25 #ifndef CGU_THREAD_H
26 #define CGU_THREAD_H
27
28 #include <memory> // for std::unique_ptr
29 #include <utility> // for std::move
30
31 #include <pthread.h>
32
33 #include <c++-gtk-utils/callback.h>
34 #include <c++-gtk-utils/mutex.h>
35 #include <c++-gtk-utils/cgu_config.h>
36
37 namespace Cgu {
38
39 namespace Thread {
40
41 /**
42 * @class Cgu::Thread::Thread thread.h c++-gtk-utils/thread.h
43 * @brief A class representing a pthread thread.
44 * @sa Thread::Mutex Thread::Mutex::Lock Thread::Cond Thread::Future Thread::JoinableHandle
45 *
46 * The Thread class encapsulates a pthread thread. It can start, join
47 * and cancel a thread.
48 *
49 * The Thread class, and the associated CancelBlock class, can be used
50 * interchangeably with (and mixed with) GThread objects and
51 * functions, and GMutex, GStaticMutex, GStaticRecMutex and GCond, as
52 * they all use pthreads underneath on POSIX and other unix-like OSes.
53 * In addition it can be used with threads started with the C++11
54 * threading facilities, as in C++11 on unix-like OSes these
55 * facilities will be built on top of pthreads (for which purpose
56 * C++11 provides the std::native_handle_type type and
57 * std::thread::native_handle() function). Even where they are not,
58 * they will use the same threading primitives provided by the kernel.
59 *
60 * @anchor ThreadsAnchor
61 * @b c++-gtk-utils @b library @b and @b C++11 @b threads
62 *
63 * As mentioned above, the thread facilities provided by this library
64 * can be freely interchanged with the threading facilities provided
65 * by C++11.
66 *
67 * The main features available from this library and not C++11 are
68 * thread cancellation and the associated Cgu::Thread::CancelBlock
69 * class, the Cgu::Thread::JoinableHandle class for scoped joinable
70 * thread handling and the Cgu::Thread::TaskManager class for running
71 * and composing tasks on a thread pool.
72 *
73 * C++11 does not provide thread cancellation or interruption support,
74 * and C++ will never be able to do so on a complete basis because to
75 * do so requires support from the underlying OS, which therefore
76 * makes it platform specific (in this case, POSIX specific):
77 * cancellation is only of limited use if it cannot reliably interrupt
78 * blocking system calls. The POSIX specification sets out the
79 * interruptible cancellation points in System Interfaces, section
80 * 2.9.5, Cancellation Points, and in effect specifies all the system
81 * calls which can block as cancellation points.
82 *
83 * Whether, in C++ programs, destructors of local objects in the
84 * cancelled thread are called is also system specific and is not
85 * specified by POSIX. Most modern commercial unixes, and recent
86 * linux/BSD distributions based on NPTL (in the case of Linux, those
87 * based on 2.6/3.* kernels), will unwind the stack and call
88 * destructors on thread cancellation by means of a pseudo-exception,
89 * but older distributions relying on the former linuxthreads
90 * implementation will not. Therefore for maximum portability
91 * cancellation would only be used where there are plain data
92 * structures/built-in types in existence in local scope when it
93 * occurs, and if there is anything in free store to be released some
94 * clean-ups would be implemented with
95 * pthread_cleanup_push()/pthread_cleanup_pop(). This should be
96 * controlled with pthread_setcancelstate() and/or the CancelBlock
97 * class to choose the cancellation point.
98 *
99 * One of the (perhaps odd) features of C++11 threads is that if the
100 * destructor of a std::thread object is called which represents a
101 * joinable thread which has not been detach()ed or join()ed, the
102 * whole program is terminated with a call to std::terminate(), which
103 * makes it difficult to use in the presence of exceptions. Often
104 * what is wanted however is for join() to be called on a joinable
105 * thread where the associated thread object goes out of scope, or
106 * (provided it is done carefully and knowingly) for detach() to be
107 * called. The Cgu::Thread::JoinableHandle class can be used where
108 * either of these two is the appropriate response to this situation.
109 *
110 * In addition, the c++-gtk-utils library provides the following which
111 * are not present in C++11: a guaranteed monotonic clock on timed
112 * condition variable waits where the operating system supports them;
113 * read-write locks; and a Cgu::Thread::Future object which is more
114 * intuitive to use than C++11 futures and features a built in
115 * Cgu::SafeEmitter object which emits when the particular task has
116 * completed, and (since version 2.0.2) has associated
117 * Cgu::Thread::Future::when() methods for passing the result to a
118 * glib main loop.
119 *
120 * @b c++-gtk-utils @b library @b and @b gthreads
121 *
122 * As mentioned above, the thread facilities provided by this library
123 * can be freely interchanged with the threading facilities provided
124 * by glib.
125 *
126 * The main features available with this thread implementation and not
127 * GThreads are thread cancellation, the mutex scoped locking classes
128 * Cgu::Thread::Mutex::Lock and Cgu::Thread::RecMutex::Lock, the
129 * joinable thread scoped management class Cgu::Thread::JoinableHandle
130 * and the Cgu::Thread::Future class (abstracting thread functions
131 * which provide a result).
132 *
133 * There is no need from the perspective of this class to call
134 * g_thread_init() before Cgu::Thread::Thread::start() is called, but
135 * prior to glib version 2.32 glib itself is not thread-safe without
136 * g_thread_init(), so where this class is used with glib < 2.32,
137 * g_thread_init() should be called at program initialization.
138 *
139 * See @ref Threading for particulars about GTK+ thread safety.
140 */
141
142
143 class Thread {
144 pthread_t thread;
145 // private constructor - this class can only be created with Thread::start
146 Thread() {}
147 public:
148 /**
149 * This class cannot be copied: it is intended to be held by
150 * std::unique_ptr. The copy constructor is deleted.
151 */
152 Thread(const Thread&) = delete;
153
154 /**
155 * This class cannot be copied: it is intended to be held by
156 * std::unique_ptr. The assignment operator is deleted.
157 */
158 Thread& operator=(const Thread&) = delete;
159
160 /**
161 * Cancels the thread represented by this Thread object. It can be
162 * called by any thread. The effect is undefined if the thread
163 * represented by this Thread object has both (a) already terminated
164 * and (b) been detached or had a call to join() made for it.
165 * Accordingly, if the user is not able to establish from the program
166 * logic whether the thread has terminated, the thread must be created
167 * as joinable and cancel() must not be called after a call to
168 * detach() has been made or a call to join() has returned. A
169 * Thread::JoinableHandle object can used to ensure this. It does not
170 * throw.
171 * @note Use this method with care - sometimes its use is unavoidable
172 * but destructors for local objects may not be called if a thread
173 * exits by virtue of a call to cancel() (that depends on the
174 * implementation). Most modern commercial unixes, and recent
175 * linux/BSD distributions based on NPTL, will unwind the stack and
176 * call destructors on thread cancellation by means of a
177 * pseudo-exception, but older distributions relying on the former
178 * linuxthreads implementation will not. Therefore for maximum
179 * portability only have plain data structures/built-in types in
180 * existence in local scope when it occurs and if there is anything in
181 * free store to be released implement some clean-ups with
182 * pthread_cleanup_push()/pthread_cleanup_pop(). This should be
183 * controlled with pthread_setcancelstate() and/or the CancelBlock
184 * class to choose the cancellation point.
185 * @sa Cgu::Thread::Exit
186 */
187 void cancel() {pthread_cancel(thread);}
188
189 /**
190 * Joins the thread represented by this Thread object (that is, waits
191 * for it to terminate). It can be called by any thread other than
192 * the one represented by this Thread object. The result is undefined
193 * if the thread is or was detached or join() has already been called
194 * for the thread (a Thread::JoinableHandle object will however give a
195 * defined result in such cases for threads originally started as
196 * joinable). It does not throw.
197 */
198 void join() {pthread_join(thread, 0);}
199
200 /**
201 * Detaches the thread represented by this Thread object where it is
202 * joinable, so as to make it unjoinable. The effect is unspecified
203 * if the thread is already unjoinable (a Thread::JoinableHandle
204 * object will however give a defined result in such cases for threads
205 * originally started as joinable). It does not throw.
206 */
207 void detach() {pthread_detach(thread);}
208
209 /**
210 * Specifies whether the calling thread is the same thread as is
211 * represented by this Thread object. The effect is undefined if the
212 * thread represented by this Thread object has both (a) already
213 * terminated and (b) been detached or had a call to join() made for
214 * it. Accordingly, if the user is not able to establish from the
215 * program logic whether the thread has terminated, the thread must be
216 * created as joinable and is_caller() must not be called after a call
217 * to detach() has been made or a call to join() has returned. A
218 * Thread::JoinableHandle object can used to ensure this. This method
219 * does not throw.
220 * @return Returns true if the caller is in the thread represented by
221 * this Thread object.
222 */
223 bool is_caller() {return pthread_equal(thread, pthread_self());}
224
225 /**
226 * Starts a new thread. It can be called by any thread.
227 * @param cb A callback object (created by Callback::make(),
228 * Callback::make_ref() or Callback::lambda()) encapsulating the
229 * function to be executed by the new thread. The Thread object
230 * returned by this function will take ownership of the callback: it
231 * will automatically be deleted either by the new thread when it has
232 * finished with it, or by this method in the calling thread if the
233 * attempt to start a new thread fails (including if std::bad_alloc is
234 * thrown).
235 * @param joinable Whether the join() method may be called in relation
236 * to the new thread.
237 * @return A Thread object representing the new thread which has been
238 * started, held by a std::unique_ptr object as it has single
239 * ownership semantics. The std::unique_ptr object will be empty
240 * (that is std::unique_ptr<Cgu::Thread::Thread>::get() will return 0)
241 * if the thread did not start correctly, which would mean that memory
242 * is exhausted, the pthread thread limit has been reached or pthread
243 * has run out of other resources to start new threads.
244 * @exception std::bad_alloc This method might throw std::bad_alloc if
245 * memory is exhausted and the system throws in that case. (This
246 * exception will not be thrown if the library has been installed
247 * using the \--with-glib-memory-slices-no-compat configuration
248 * option: instead glib will terminate the program if it is unable to
249 * obtain memory from the operating system.) If this exception is
250 * thrown, the thread will not have started.
251 * @note 1. The thread will keep running even if the return value of
252 * start() goes out of scope (but it will no longer be possible to
253 * call any of the methods in this class for it, which is fine if the
254 * thread is not started as joinable and it is not intended to cancel
255 * it).
256 * @note 2. If the thread is started with the joinable attribute, the
257 * user must subsequently either call the join() or the detach()
258 * method, as otherwise a resource leak may occur (the destructor of
259 * this class does not call detach() automatically). Alternatively,
260 * the return value of this method can be passed to a
261 * Thread::JoinableHandle object which will do this automatically in
262 * the Thread::JoinableHandle object's destructor.
263 * @note 3. Any Thread::Exit exception thrown from the function
264 * executed by the new thread will be caught and consumed. The thread
265 * will safely terminate and unwind the stack in so doing.
266 * @note 4. If any uncaught exception other than Thread::Exit is
267 * allowed to propagate from the initial function executed by the new
268 * thread, the exception is not consumed (NPTL's forced stack
269 * unwinding on cancellation does not permit catching with an ellipsis
270 * argument without rethrowing, and even if it did permit it, the
271 * result would be an unreported error). The C++11 standard requires
272 * std::terminate() to be called in such a case and so the entire
273 * program terminated. Accordingly, a user must make sure that no
274 * exceptions, other than Thread::Exit or any cancellation
275 * pseudo-exception, can propagate from the initial function executed
276 * by the new thread. This includes ensuring that, for any argument
277 * passed to that function which is not a built-in type and which is
278 * not taken by the function by const or non-const reference, the
279 * argument type's copy constructor does not throw.
280 */
281 static std::unique_ptr<Cgu::Thread::Thread> start(const Cgu::Callback::Callback* cb,
282 bool joinable);
283
284 /**
285 * Starts a new thread. It can be called by any thread.
286 * @param func A callable object, such as formed by a lambda
287 * expression or the result of std::bind, which will be executed by
288 * the new thread.
289 * @param joinable Whether the join() method may be called in relation
290 * to the new thread.
291 * @return A Thread object representing the new thread which has been
292 * started, held by a std::unique_ptr object as it has single
293 * ownership semantics. The std::unique_ptr object will be empty
294 * (that is std::unique_ptr<Cgu::Thread::Thread>::get() will return 0)
295 * if the thread did not start correctly, which would mean that memory
296 * is exhausted, the pthread thread limit has been reached or pthread
297 * has run out of other resources to start new threads.
298 * @exception std::bad_alloc This method might throw std::bad_alloc if
299 * memory is exhausted and the system throws in that case. (This
300 * exception will not be thrown if the library has been installed
301 * using the \--with-glib-memory-slices-no-compat configuration
302 * option: instead glib will terminate the program if it is unable to
303 * obtain memory from the operating system.) If this exception is
304 * thrown, the thread will not have started.
305 * @note 1. This function may also throw if the copy or move
306 * constructor of the callable object throws. If that happens, the
307 * thread will not have started.
308 * @note 2. The thread will keep running even if the return value of
309 * start() goes out of scope (but it will no longer be possible to
310 * call any of the methods in this class for it, which is fine if the
311 * thread is not started as joinable and it is not intended to cancel
312 * it).
313 * @note 3. If the thread is started with the joinable attribute, the
314 * user must subsequently either call the join() or the detach()
315 * method, as otherwise a resource leak may occur (the destructor of
316 * this class does not call detach() automatically). Alternatively,
317 * the return value of this method can be passed to a
318 * Thread::JoinableHandle object which will do this automatically in
319 * the Thread::JoinableHandle object's destructor.
320 * @note 4. Any Thread::Exit exception thrown from the function
321 * executed by the new thread will be caught and consumed. The thread
322 * will safely terminate and unwind the stack in so doing.
323 * @note 5. If any uncaught exception other than Thread::Exit is
324 * allowed to propagate from the initial function executed by the new
325 * thread, the exception is not consumed (NPTL's forced stack
326 * unwinding on cancellation does not permit catching with an ellipsis
327 * argument without rethrowing, and even if it did permit it, the
328 * result would be an unreported error). The C++11 standard requires
329 * std::terminate() to be called in such a case and so the entire
330 * program terminated. Accordingly, a user must make sure that no
331 * exceptions, other than Thread::Exit or any cancellation
332 * pseudo-exception, can propagate from the initial function executed
333 * by the new thread. This includes ensuring that, for any bound
334 * argument passed to that function which is not a built-in type and
335 * which is not taken by the function by const or non-const reference,
336 * the argument type's copy constructor does not throw.
337 *
338 * Since 2.1.0
339 */
340 // we need to use enable_if so that where this function is passed a
341 // pointer to non-const Callback::Callback, or some other convertible
342 // pointer, this templated overload is dropped from the overload set,
343 // in order to support the Callback::Callback pointer overloads of
344 // this function. This overload calls into the version of this
345 // function taking a pointer to const Callback::Callback in order to
346 // perform type erasure.
347 template <class F,
348 class = typename std::enable_if<!std::is_convertible<typename std::remove_reference<F>::type,
349 const Cgu::Callback::Callback*>::value>::type>
350 static std::unique_ptr<Cgu::Thread::Thread> start(F&& func,
351 bool joinable) {
352 return start(Cgu::Callback::lambda<>(std::forward<F>(func)), joinable);
353 }
354
355 #ifdef CGU_USE_GLIB_MEMORY_SLICES_NO_COMPAT
356 CGU_GLIB_MEMORY_SLICES_FUNCS
357 #endif
358 };
359
360 /**
361 * @class Cgu::Thread::JoinableHandle thread.h c++-gtk-utils/thread.h
362 * @brief A class wrapping a Thread::Thread object representing a
363 * joinable thread.
364 * @sa Thread::Thread Thread::Future
365 *
366 * This class enables a joinable thread to be made more easily
367 * exception safe. It can also be used to provide that a joinable
368 * thread is not detached or joined while other methods dependent on
369 * that might still be called, and to provide a defined result where
370 * there are multiple calls to join() and/or detach(). When it is
371 * destroyed, it will either detach or join the thread represented by
372 * the wrapped Thread::Thread object unless it has previously been
373 * detached or joined using the detach() or join() methods, so
374 * avoiding thread resource leaks. Whether it will detach() or join()
375 * on destruction depends on the Thread::JoinableHandle::Action
376 * argument passed to the
377 * Thread::JoinableHandle::JoinableHandle(std::unique_ptr<Thread::Thread>,
378 * Action) constructor.
379 *
380 * Passing Thread::JoinableHandle::detach_on_exit to that argument is
381 * not always the correct choice where the thread callback has been
382 * bound to a reference argument in local scope and an exception might
383 * be thrown, because the thread will keep running after the
384 * Thread::JoinableHandle object and other local variables have
385 * (because of the exception) gone out of scope. Consider the
386 * following trivial parallelized calculation example:
387 *
388 * @code
389 * std::vector<int> get_readings();
390 * void get_mean(const std::vector<int>& v, int& result);
391 * void get_std_deviation(const std::vector<int>& v, int& result); // might throw
392 * void show_result(int mean, int deviation);
393 *
394 * using namespace Cgu;
395 * void do_calc() {
396 * int i, j;
397 * std::vector<int> v = get_readings();
398 * std::unique_ptr<Thread::Thread> t =
399 * Thread::Thread::start(std::bind(&get_mean, std::cref(v), std::ref(i)), true);
400 * if (t.get()) { // checks whether thread started correctly
401 * get_std_deviation(v, j);
402 * t->join();
403 * show_result(i, j);
404 * }
405 * }
406 * @endcode
407 *
408 * If get_std_deviation() throws, as well as there being a potential
409 * thread resource leak by virtue of no join being made, the thread
410 * executing get_mean() will continue running and attempt to access
411 * variable v, and put its result in variable i, which may by then
412 * both be out of scope. To deal with such a case, the thread could
413 * be wrapped in a Thread::JoinableHandle object which joins on exit
414 * rather than detaches, for example:
415 *
416 * @code
417 * ...
418 * using namespace Cgu;
419 * void do_calc() {
420 * int i, j;
421 * std::vector<int> v = get_readings();
422 * Thread::JoinableHandle t{Thread::Thread::start(std::bind(&get_mean, std::cref(v), std::ref(i)), true),
423 * Thread::JoinableHandle::join_on_exit};
424 * if (t.is_managing()) { // checks whether thread started correctly
425 * get_std_deviation(v, j);
426 * t.join();
427 * show_result(i, j);
428 * }
429 * }
430 * @endcode
431 *
432 * Better still, however, would be to use Cgu::Thread::Future in this
433 * kind of usage, namely a usage where a worker thread is intended to
434 * provide a result for inspection.
435 *
436 * @note These examples assume that the std::vector library
437 * implementation permits concurrent reads of a vector object by
438 * different threads. Whether that is the case depends on the
439 * documentation of the library concerned (if designed for a
440 * multi-threaded environment, most will permit this).
441 */
442 class JoinableHandle {
443 public:
444 enum Action {detach_on_exit, join_on_exit};
445
446 private:
447 Mutex mutex; // make this the first member so the constructors are strongly exception safe
448 Action action;
449 bool detached;
450 std::unique_ptr<Cgu::Thread::Thread> thread;
451
452 public:
453 /**
454 * Cancels the thread represented by the wrapped Thread::Thread
455 * object. It can be called by any thread. The effect is undefined
456 * if when called the thread represented by the wrapped Thread::Thread
457 * object has both (a) already terminated and (b) had a call to join()
458 * or detach() made for it. Accordingly, if the user is not able to
459 * establish from the program logic whether the thread has terminated,
460 * cancel() must not be called after a call to detach() has been made
461 * or a call to join() has returned: this can be ensured by only
462 * detaching or joining via this object's destructor (that is, by not
463 * using the explicit detach() and join() methods). This method does
464 * not throw.
465 * @note Use this method with care - see Thread::cancel() for further
466 * information.
467 */
468 void cancel();
469
470 /**
471 * Joins the thread represented by the wrapped Thread::Thread object
472 * (that is, waits for it to terminate), unless the detach() or join()
473 * method has previously been called in which case this call does
474 * nothing. It can be called by any thread other than the one
475 * represented by the wrapped Thread::Thread object, but only one
476 * thread can wait on it: if one thread (thread A) calls it while
477 * another thread (thread B) is already blocking on it, thread A's
478 * call to this method will return immediately and return false. It
479 * does not throw.
480 * @return true if a successful join() has been accomplished (that is,
481 * detach() or join() have not previously been called), otherwise
482 * false.
483 */
484 bool join();
485
486 /**
487 * Detaches the thread represented by this Thread::Thread object, so
488 * as to make it unjoinable, unless the detach() or join() method has
489 * previously been called in which case this call does nothing. It
490 * does not throw.
491 */
492 void detach();
493
494 /**
495 * Specifies whether the calling thread is the same thread as is
496 * represented by the wrapped Thread::Thread object. It can be called
497 * by any thread. The effect is undefined if the thread represented
498 * by the wrapped Thread::Thread object has both (a) already
499 * terminated and (b) had a call to join() or detach() made for it.
500 * Accordingly, if the user is not able to establish from the program
501 * logic whether the thread has terminated, is_caller() must not be
502 * called after a call to detach() has been made or a call to join()
503 * has returned: this can be ensured by only detaching or joining via
504 * this object's destructor (that is, by not using the explicit
505 * detach() and join() methods). This method does not throw.
506 * @return Returns true if the caller is in the thread represented by
507 * the wrapped Thread::Thread object. If not, or this JoinableHandle
508 * does not wrap any Thread object, then returns false.
509 */
510 bool is_caller();
511
512 /**
513 * Specifies whether this JoinableHandle object has been initialized
514 * with a Thread::Thread object representing a correctly started
515 * thread in respect of which neither JoinableHandle::detach() nor
516 * JoinableHandle::join() has been called. It can be called by any
517 * thread. It is principally intended to enable the constructor
518 * taking a std::unique_ptr<Cgu::Thread::Thread> object to be directly
519 * initialized by a call to Thread::Thread::start(), by providing a
520 * means for the thread calling Thread::Thread::start() to check
521 * afterwards that the new thread did, in fact, start correctly. Note
522 * that this method will return true even after the thread has
523 * finished, provided neither the join() nor detach() method has been
524 * called.
525 * @return Returns true if this object has been initialized by a
526 * Thread::Thread object representing a correctly started thread in
527 * respect of which neither JoinableHandle::detach() nor
528 * JoinableHandle::join() has been called, otherwise false.
529 */
530 bool is_managing();
531
532 /**
533 * Moves one JoinableHandle object to another JoinableHandle object.
534 * This is a move operation which transfers ownership to the assignee,
535 * as the handles store their Thread::Thread object by
536 * std::unique_ptr<>. Any existing thread managed by the assignee
537 * prior to the move will be detached if it has not already been
538 * detached or joined. This method will not throw.
539 * @param h The assignor/movant, which will cease to hold a valid
540 * Thread::Thread object after the move has taken place.
541 * @return A reference to the assignee JoinableHandle object after
542 * assignment.
543 * @note This method is thread safe as regards the assignee (the
544 * object assigned to), but no synchronization is carried out with
545 * respect to the rvalue assignor/movant. This is because temporaries
546 * are only visible and accessible in the thread carrying out the move
547 * operation and synchronization for them would represent pointless
548 * overhead. In a case where the user uses std::move to force a move
549 * from a named object, and that named object's lifetime is managed by
550 * (or the object is otherwise accessed by) a different thread than
551 * the one making the move, the user must carry out her own
552 * synchronization with respect to that different thread, as the named
553 * object will be mutated by the move.
554 */
555 JoinableHandle& operator=(JoinableHandle&& h);
556
557 /**
558 * This constructor initializes a new JoinableHandle object with a
559 * std::unique_ptr<Thread::Thread> object, as provided by
560 * Thread::Thread::start(). This is a move operation which transfers
561 * ownership to the new object.
562 * @param thr The initializing Thread::Thread object (which must have
563 * been created as joinable) passed by a std::unique_ptr smart
564 * pointer. This is a move operation.
565 * @param act Either Thread::JoinableHandle::detach_on_exit (which
566 * will cause the destructor to detach the thread if it has not
567 * previously been detached or joined) or
568 * Thread::JoinableHandle::join_on_exit (which will cause the
569 * destructor to join the thread if it has not previously been
570 * detached or joined).
571 * @exception Cgu::Thread::MutexError Throws this exception if
572 * initialization of the internal mutex fails. The constructor is
573 * strongly exception safe: if Cgu::Thread::MutexError is thrown, the
574 * initializing std::unique_ptr<Cgu::Thread::Thread> object will be
575 * left unchanged. (It is often not worth checking for this
576 * exception, as it means either memory is exhausted or pthread has
577 * run out of other resources to create new mutexes.)
578 * @note 1. It is not necessary to check that the thread parameter
579 * represents a correctly started thread (that is, that thr.get() does
580 * not return 0) before this constructor is invoked, because that can
581 * be done after construction by calling JoinableHandle::is_managing()
582 * (a JoinableHangle object can safely handle a case where thr.get()
583 * does return 0). This enables a JoinableHandle object to be
584 * directly initialized by this constructor from a call to
585 * Thread::Thread::start().
586 * @note 2. No synchronization is carried out with respect to the
587 * initializing std::unique_ptr object. This is because such an
588 * object is usually passed to this constructor as a temporary, which
589 * is only visible and accessible in the thread carrying out the move
590 * operation, in which case synchronization would represent pointless
591 * overhead. In a case where the user uses std::move to force a move
592 * from a named std::unique_ptr object, and that named object's
593 * lifetime is managed by (or the object is otherwise accessed by) a
594 * different thread than the one making the move, the user must carry
595 * out her own synchronization with respect to that different thread,
596 * as the initializing std::unique_ptr object will be mutated by the
597 * move.
598 * @sa JoinableHandle::is_managing().
599 */
600 JoinableHandle(std::unique_ptr<Cgu::Thread::Thread> thr, Action act): action(act), detached(false), thread(std::move(thr)) {}
601
602 /**
603 * This constructor initializes a new JoinableHandle object with an
604 * existing JoinableHandle object. This is a move operation which
605 * transfers ownership to the new object.
606 * @param h The initializing JoinableHandle object, which will cease
607 * to hold a valid Thread::Thread object after the initialization has
608 * taken place.
609 * @exception Cgu::Thread::MutexError Throws this exception if
610 * initialization of the internal mutex fails. The constructor is
611 * strongly exception safe: if Cgu::Thread::MutexError is thrown, the
612 * initializing Cgu::Thread::JoinableHandle object will be left
613 * unchanged. (It is often not worth checking for this exception, as
614 * it means either memory is exhausted or pthread has run out of other
615 * resources to create new mutexes.)
616 * @note No synchronization is carried out with respect to the
617 * initializing rvalue. This is because temporaries are only visible
618 * and accessible in the thread carrying out the move operation and
619 * synchronization for them would represent pointless overhead. In a
620 * case where a user uses std::move to force a move from a named
621 * object, and that named object's lifetime is managed by (or the
622 * object is otherwise accessed by) a different thread than the one
623 * making the move, the user must carry out her own synchronization
624 * with respect to that different thread, as the named object will be
625 * mutated by the move.
626 */
627 JoinableHandle(JoinableHandle&& h): action(h.action), detached(h.detached), thread(std::move(h.thread)) {}
628
629 /**
630 * The default constructor. Nothing is managed until the move
631 * assignment operator has been called.
632 * @exception Cgu::Thread::MutexError Throws this exception if
633 * initialization of the internal mutex fails. (It is often not worth
634 * checking for this exception, as it means either memory is exhausted
635 * or pthread has run out of other resources to create new mutexes.)
636 *
637 * Since 2.0.8
638 */
639 JoinableHandle(): action(detach_on_exit), detached(true) {}
640
641 /**
642 * The destructor will detach a managed thread (if the
643 * Thread::JoinableHandle::detach_on_exit flag is set) or join it (if
644 * the Thread::JoinableHandle::join_on_exit flag is set), unless it
645 * has previously been detached or joined with the detach() or join()
646 * methods. The destructor is thread safe (any thread may destroy the
647 * JoinableHandle object). The destructor will not throw.
648 */
649 ~JoinableHandle();
650
651 /* Only has effect if --with-glib-memory-slices-compat or
652 * --with-glib-memory-slices-no-compat option picked */
653 CGU_GLIB_MEMORY_SLICES_FUNCS
654 };
655
656 /**
657 * @class CancelBlock thread.h c++-gtk-utils/thread.h
658 * @brief A class enabling the cancellation state of a thread to be
659 * controlled.
660 *
661 * A class enabling the cancellation state of a thread to be
662 * controlled, so as to provide exception safe cancellation state
663 * changes. When a CancelBlock object goes out of scope, the thread's
664 * cancellation state is returned to the state it was in immediately
665 * prior to the object's construction.
666 *
667 * Cancellation state can be changed before a CancelBlock object goes
668 * out of scope by calling its block() and unblock() methods.
669 * However, care should be taken if calling unblock() for the purpose
670 * of enabling thread cancellation while the CancelBlock object is
671 * still in existence: this should normally only be done if the
672 * thread's cancellation state at the time the CancelBlock object was
673 * constructed (which is the cancellation state to which the thread
674 * will be restored when the object goes out of scope) was
675 * PTHREAD_CANCEL_DISABLE. This is because when a thread begins
676 * cancellation the POSIX standard states that it will automatically
677 * switch itself into a PTHREAD_CANCEL_DISABLE state (see System
678 * Interfaces, section 2.9.5, Thread Cancellation Cleanup Handlers),
679 * and the POSIX standard further states that the behaviour is
680 * undefined if a cancellation handler attempts to enable cancellation
681 * again while the thread is cleaning up - and any thread
682 * implementation such as NPTL which unwinds the stack on cancellation
683 * will do so if the CancelBlock's destructor would restore to
684 * PTHREAD_CANCEL_ENABLE state. Whilst it is to be expected that any
685 * cancellation stack unwinding implementation will behave sensibly in
686 * these circumstances, this is not mandated by POSIX, so making code
687 * relying on this less portable.
688 *
689 * For these reasons, the same care should be exercised if passing
690 * 'false' to the CancelBlock constructor's 'blocking' argument.
691 */
692
693 class CancelBlock {
694 int starting_state;
695 public:
696 /**
697 * This class cannot be copied. The copy constructor is deleted.
698 */
699 CancelBlock(const CancelBlock&) = delete;
700
701 /**
702 * This class cannot be copied. The assignment operator is deleted.
703 */
704 CancelBlock& operator=(const CancelBlock&) = delete;
705
706 /**
707 * Makes the thread uncancellable, even if the code passes through a
708 * cancellation point, while the CancelBlock object exists (when the
709 * CancelBlock object ceases to exist, cancellation state is returned
710 * to the state prior to it being constructed). It should only be
711 * called by the thread which created the CancelBlock object. This
712 * method will not throw.
713 * @param old_state Indicates the cancellation state of the calling
714 * thread immediately before this call to block() was made, either
715 * PTHREAD_CANCEL_ENABLE (if the thread was previously cancellable) or
716 * PTHREAD_CANCEL_DISABLE (if this call did nothing because the thread
717 * was already uncancellable).
718 * @return 0 if successful, else a value other than 0.
719 */
720 static int block(int& old_state) {return pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_state);}
721
722 /**
723 * Makes the thread uncancellable, even if the code passes through a
724 * cancellation point, while the CancelBlock object exists (when the
725 * CancelBlock object ceases to exist, cancellation state is returned
726 * to the state prior to it being constructed). It should only be
727 * called by the thread which created the CancelBlock object. This
728 * method will not throw.
729 * @return 0 if successful, else a value other than 0.
730 */
731 static int block() {int old_state; return block(old_state);}
732
733 /**
734 * Makes the thread cancellable while the CancelBlock object exists
735 * (when the CancelBlock object ceases to exist, cancellation state is
736 * returned to the state prior to it being constructed). It should
737 * only be called by the thread which created the CancelBlock object.
738 * This method will not throw. The 'Detailed Description' section
739 * above has information about the issues to be taken into account if
740 * a call to this method is to be made.
741 * @param old_state Indicates the cancellation state of the calling
742 * thread immediately before this call to unblock() was made, either
743 * PTHREAD_CANCEL_DISABLE (if the thread was previously uncancellable)
744 * or PTHREAD_CANCEL_ENABLE (if this call did nothing because the
745 * thread was already cancellable).
746 * @return 0 if successful, else a value other than 0.
747 */
748 static int unblock(int& old_state) {return pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &old_state);}
749
750 /**
751 * Makes the thread cancellable while the CancelBlock object exists
752 * (when the CancelBlock object ceases to exist, cancellation state is
753 * returned to the state prior to it being constructed). It should
754 * only be called by the thread which created the CancelBlock object.
755 * This method will not throw. The 'Detailed Description' section
756 * above has information about the issues to be taken into account if
757 * a call to this method is to be made.
758 * @return 0 if successful, else a value other than 0.
759 */
760 static int unblock() {int old_state; return unblock(old_state);}
761
762 /**
763 * Restores cancellation state to the state it was in immediately
764 * before this CancelBlock object was constructed. It should only be
765 * called by the thread which created the CancelBlock object. This
766 * method will not throw.
767 * @param old_state Indicates the cancellation state of the calling
768 * thread immediately before this call to restore() was made, either
769 * PTHREAD_CANCEL_DISABLE (if the thread was previously uncancellable)
770 * or PTHREAD_CANCEL_ENABLE (if this thread was previously
771 * cancellable).
772 * @return 0 if successful, else a value other than 0.
773 */
774 int restore(int& old_state) {return pthread_setcancelstate(starting_state, &old_state);}
775
776 /**
777 * Restores cancellation state to the state it was in immediately
778 * before this CancelBlock object was constructed. It should only be
779 * called by the thread which created the CancelBlock object. This
780 * method will not throw.
781 * @return 0 if successful, else a value other than 0.
782 */
783 int restore() {int old_state; return restore(old_state);}
784
785 /**
786 * The constructor will not throw.
787 * @param blocking Whether the CancelBlock object should start in
788 * blocking mode. The 'Detailed Description' section above has
789 * information about the issues to be taken into account if 'false' is
790 * passed to this parameter.
791 */
792 CancelBlock(bool blocking = true);
793
794 /**
795 * The destructor will put the thread in the cancellation state that
796 * it was in immediately before the CancelBlock object was constructed
797 * (which might be blocking). It will not throw.
798 */
799 ~CancelBlock() {restore();}
800
801 /* Only has effect if --with-glib-memory-slices-compat or
802 * --with-glib-memory-slices-no-compat option picked */
803 CGU_GLIB_MEMORY_SLICES_FUNCS
804 };
805
806 /**
807 * @class Exit thread.h c++-gtk-utils/thread.h
808 * @brief A class which can be thrown to terminate the throwing
809 * thread.
810 *
811 * This class can be thrown (instead of calling pthread_exit()) when a
812 * thread wishes to terminate itself and also ensure stack unwinding,
813 * so that destructors of local objects are called. It is caught
814 * automatically by the implementation of Cgu::Thread::Thread::start()
815 * so that it will only terminate the thread throwing it and not the
816 * whole process. See the Cgu::Thread::Thread::cancel() method above,
817 * for use when a thread wishes to terminate another one, and the
818 * caveats on the use of Cgu::Thread::Thread::cancel().
819 *
820 * Do not throw a Cgu::Thread::Exit object in a program with more than
821 * one main loop in order to terminate one of the threads which has
822 * its own main loop. Instead, just cause its main loop to terminate
823 * by, say, calling g_main_loop_quit() on it.
824 */
825 class Exit {};
826
827 } // namespace Thread
828
829 } // namespace Cgu
830
831 #endif