## Signals

Signals — A means for customization of object behaviour and a general purpose notification mechanism

## Synopsis

    #include <glib-object.h>

                        GSignalInvocationHint;
    gboolean            (*GSignalAccumulator)               (GSignalInvocationHint *ihint,
                                                             GValue *return_accu,
                                                             const GValue *handler_return,
                                                             gpointer data);
    typedef             GSignalCMarshaller;
    gboolean            (*GSignalEmissionHook)              (GSignalInvocationHint *ihint,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer data);
    enum                GSignalFlags;
    enum                GSignalMatchType;
                        GSignalQuery;
    #define             G_SIGNAL_TYPE_STATIC_SCOPE
    #define             G_SIGNAL_MATCH_MASK
    #define             G_SIGNAL_FLAGS_MASK
    guint               g_signal_new                        (const gchar *signal_name,
                                                             GType itype,
                                                             GSignalFlags signal_flags,
                                                             guint class_offset,
                                                             GSignalAccumulator accumulator,
                                                             gpointer accu_data,
                                                             GSignalCMarshaller c_marshaller,
                                                             GType return_type,
                                                             guint n_params,
                                                             ...);
    guint               g_signal_newv                       (const gchar *signal_name,
                                                             GType itype,
                                                             GSignalFlags signal_flags,
                                                             GClosure *class_closure,
                                                             GSignalAccumulator accumulator,
                                                             gpointer accu_data,
                                                             GSignalCMarshaller c_marshaller,
                                                             GType return_type,
                                                             guint n_params,
                                                             GType *param_types);
    guint               g_signal_new_valist                 (const gchar *signal_name,
                                                             GType itype,
                                                             GSignalFlags signal_flags,
                                                             GClosure *class_closure,
                                                             GSignalAccumulator accumulator,
                                                             gpointer accu_data,
                                                             GSignalCMarshaller c_marshaller,
                                                             GType return_type,
                                                             guint n_params,
                                                             va_list args);
    void                g_signal_query                      (guint signal_id,
                                                             GSignalQuery *query);
    guint               g_signal_lookup                     (const gchar *name,
                                                             GType itype);
    const gchar*        g_signal_name                       (guint signal_id);
    guint*              g_signal_list_ids                   (GType itype,
                                                             guint *n_ids);
    void                g_signal_emit                       (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             ...);
    void                g_signal_emit_by_name               (gpointer instance,
                                                             const gchar *detailed_signal,
                                                             ...);
    void                g_signal_emitv                      (const GValue *instance_and_params,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GValue *return_value);
    void                g_signal_emit_valist                (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             va_list var_args);
    #define             g_signal_connect                    (instance, detailed_signal, c_handler, data)
    #define             g_signal_connect_after              (instance, detailed_signal, c_handler, data)
    #define             g_signal_connect_swapped            (instance, detailed_signal, c_handler, data)
    gulong              g_signal_connect_object             (gpointer instance,
                                                             const gchar *detailed_signal,
                                                             GCallback c_handler,
                                                             gpointer gobject,
                                                             GConnectFlags connect_flags);
    enum                GConnectFlags;
    gulong              g_signal_connect_data               (gpointer instance,
                                                             const gchar *detailed_signal,
                                                             GCallback c_handler,
                                                             gpointer data,
                                                             GClosureNotify destroy_data,
                                                             GConnectFlags connect_flags);
    gulong              g_signal_connect_closure            (gpointer instance,
                                                             const gchar *detailed_signal,
                                                             GClosure *closure,
                                                             gboolean after);
    gulong              g_signal_connect_closure_by_id      (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gboolean after);
    void                g_signal_handler_block              (gpointer instance,
                                                             gulong handler_id);
    void                g_signal_handler_unblock            (gpointer instance,
                                                             gulong handler_id);
    void                g_signal_handler_disconnect         (gpointer instance,
                                                             gulong handler_id);
    gulong              g_signal_handler_find               (gpointer instance,
                                                             GSignalMatchType mask,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gpointer func,
                                                             gpointer data);
    guint               g_signal_handlers_block_matched     (gpointer instance,
                                                             GSignalMatchType mask,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gpointer func,
                                                             gpointer data);
    guint               g_signal_handlers_unblock_matched   (gpointer instance,
                                                             GSignalMatchType mask,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gpointer func,
                                                             gpointer data);
    guint               g_signal_handlers_disconnect_matched
                                                            (gpointer instance,
                                                             GSignalMatchType mask,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gpointer func,
                                                             gpointer data);
    gboolean            g_signal_handler_is_connected       (gpointer instance,
                                                             gulong handler_id);
    #define             g_signal_handlers_block_by_func     (instance, func, data)
    #define             g_signal_handlers_unblock_by_func   (instance, func, data)
    #define             g_signal_handlers_disconnect_by_func(instance, func, data)
    gboolean            g_signal_has_handler_pending        (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             gboolean may_be_blocked);
    void                g_signal_stop_emission              (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail);
    void                g_signal_stop_emission_by_name      (gpointer instance,
                                                             const gchar *detailed_signal);
    void                g_signal_override_class_closure     (guint signal_id,
                                                             GType instance_type,
                                                             GClosure *class_closure);
    void                g_signal_chain_from_overridden      (const GValue *instance_and_params,
                                                             GValue *return_value);
    guint               g_signal_new_class_handler          (const gchar *signal_name,
                                                             GType itype,
                                                             GSignalFlags signal_flags,
                                                             GCallback class_handler,
                                                             GSignalAccumulator accumulator,
                                                             gpointer accu_data,
                                                             GSignalCMarshaller c_marshaller,
                                                             GType return_type,
                                                             guint n_params,
                                                             ...);
    void                g_signal_override_class_handler     (const gchar *signal_name,
                                                             GType instance_type,
                                                             GCallback class_handler);
    void                g_signal_chain_from_overridden_handler
                                                            (gpointer instance,
                                                             ...);
    gulong              g_signal_add_emission_hook          (guint signal_id,
                                                             GQuark detail,
                                                             GSignalEmissionHook hook_func,
                                                             gpointer hook_data,
                                                             GDestroyNotify data_destroy);
    void                g_signal_remove_emission_hook       (guint signal_id,
                                                             gulong hook_id);
    gboolean            g_signal_parse_name                 (const gchar *detailed_signal,
                                                             GType itype,
                                                             guint *signal_id_p,
                                                             GQuark *detail_p,
                                                             gboolean force_detail_quark);
    GSignalInvocationHint* g_signal_get_invocation_hint     (gpointer instance);
    GClosure*           g_signal_type_cclosure_new          (GType itype,
                                                             guint struct_offset);
    gboolean            g_signal_accumulator_true_handled   (GSignalInvocationHint *ihint,
                                                             GValue *return_accu,
                                                             const GValue *handler_return,
                                                             gpointer dummy);

## Description

The basic concept of the signal system is that of the emission of a signal. Signals are introduced per-type and are identified through strings. Signals introduced for a parent type are available in derived types as well, so basically they are a per-type facility that is inherited. A signal emission mainly involves invocation of a certain set of callbacks in precisely defined manner. There are two main categories of such callbacks, per-object [12] ones and user provided ones. The per-object callbacks are most often referred to as "object method handler" or "default (signal) handler", while user provided callbacks are usually just called "signal handler". The object method handler is provided at signal creation time (this most frequently happens at the end of an object class' creation), while user provided handlers are frequently connected and disconnected to/from a certain signal on certain object instances.

A signal emission consists of five stages, unless prematurely stopped:

| 1 - Invocation of the object method handler for `G_SIGNAL_RUN_FIRST` signals
| 2 - Invocation of normal user-provided signal handlers (after flag `FALSE`)
| 3 - Invocation of the object method handler for `G_SIGNAL_RUN_LAST` signals
| 4 - Invocation of user provided signal handlers, connected with an after flag of `TRUE`
| 5 - Invocation of the object method handler for `G_SIGNAL_RUN_CLEANUP` signals

The user-provided signal handlers are called in the order they were connected in. All handlers may prematurely stop a signal emission, and any number of handlers may be connected, disconnected, blocked or unblocked during a signal emission. There are certain criteria for skipping user handlers in stages 2 and 4 of a signal emission. First, user handlers may be blocked, blocked handlers are omitted during callback invocation, to return from the "blocked" state, a handler has to get unblocked exactly the same amount of times it has been blocked before. Second, upon emission of a `G_SIGNAL_DETAILED` signal, an additional "detail" argument passed in to `g_signal_emit()` has to match the detail argument of the signal handler currently subject to invocation. Specification of no detail argument for signal handlers (omission of the detail part of the signal specification upon connection) serves as a wildcard and matches any detail argument passed in to emission.

## Details

### GSignalInvocationHint

    typedef struct {
      guint		signal_id;
      GQuark	detail;
      GSignalFlags	run_type;
    } GSignalInvocationHint;

The GSignalInvocationHint structure is used to pass on additional information to callbacks during a signal emission.

guint `signal_id`; | The signal id of the signal invoking the callback
GQuark `detail`; | The detail passed on for this emission
GSignalFlags `run_type`; | The stage the signal emission is currently in, this field will contain one of `G_SIGNAL_RUN_FIRST`, `G_SIGNAL_RUN_LAST` or `G_SIGNAL_RUN_CLEANUP`.

### GSignalAccumulator ()

    gboolean            (*GSignalAccumulator)               (GSignalInvocationHint *ihint,
                                                             GValue *return_accu,
                                                             const GValue *handler_return,
                                                             gpointer data);

The signal accumulator is a special callback function that can be used to collect return values of the various callbacks that are called during a signal emission. The signal accumulator is specified at signal creation time, if it is left `NULL`, no accumulation of callback return values is performed. The return value of signal emissions is then the value returned by the last callback.

`ihint` : | Signal invocation hint, see GSignalInvocationHint.
`return_accu` : | Accumulator to collect callback return values in, this is the return value of the current signal emission.
`handler_return` : | A GValue holding the return value of the signal handler.
`data` : | Callback data that was specified when creating the signal.
Returns : | The accumulator function returns whether the signal emission should be aborted. Returning `FALSE` means to abort the current emission and `TRUE` is returned for continuation.

### GSignalCMarshaller

    typedef GClosureMarshal			 GSignalCMarshaller;

This is the signature of marshaller functions, required to marshall arrays of parameter values to signal emissions into C language callback invocations. It is merely an alias to GClosureMarshal since the GClosure mechanism takes over responsibility of actual function invocation for the signal system.

### GSignalEmissionHook ()

    gboolean            (*GSignalEmissionHook)              (GSignalInvocationHint *ihint,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer data);

A simple function pointer to get invoked when the signal is emitted. This allows you to tie a hook to the signal type, so that it will trap all emissions of that signal, from any object.

You may not attach these to signals created with the G_SIGNAL_NO_HOOKS flag.

`ihint` : | Signal invocation hint, see GSignalInvocationHint.
`n_param_values` : | the number of parameters to the function, including the instance on which the signal was emitted.
`param_values` : | the instance on which the signal was emitted, followed by the parameters of the emission.
`data` : | user data associated with the hook.
Returns : | whether it wants to stay connected. If it returns `FALSE`, the signal hook is disconnected (and destroyed).

### enum GSignalFlags

    typedef enum
    {
      G_SIGNAL_RUN_FIRST	= 1 << 0,
      G_SIGNAL_RUN_LAST	= 1 << 1,
      G_SIGNAL_RUN_CLEANUP	= 1 << 2,
      G_SIGNAL_NO_RECURSE	= 1 << 3,
      G_SIGNAL_DETAILED	= 1 << 4,
      G_SIGNAL_ACTION	= 1 << 5,
      G_SIGNAL_NO_HOOKS	= 1 << 6
    } GSignalFlags;

The signal flags are used to specify a signal's behaviour, the overall signal description outlines how especially the RUN flags control the stages of a signal emission.

`G_SIGNAL_RUN_FIRST` | Invoke the object method handler in the first emission stage.
`G_SIGNAL_RUN_LAST` | Invoke the object method handler in the third emission stage.
`G_SIGNAL_RUN_CLEANUP` | Invoke the object method handler in the last emission stage.
`G_SIGNAL_NO_RECURSE` | Signals being emitted for an object while currently being in emission for this very object will not be emitted recursively, but instead cause the first emission to be restarted.
`G_SIGNAL_DETAILED` | This signal supports "::detail" appendices to the signal name upon handler connections and emissions.
`G_SIGNAL_ACTION` | Action signals are signals that may freely be emitted on alive objects from user code via `g_signal_emit()` and friends, without the need of being embedded into extra code that performs pre or post emission adjustments on the object. They can also be thought of as object methods which can be called generically by third-party code.
`G_SIGNAL_NO_HOOKS` | No emissions hooks are supported for this signal.

### enum GSignalMatchType

    typedef enum
    {
      G_SIGNAL_MATCH_ID	   = 1 << 0,
      G_SIGNAL_MATCH_DETAIL	   = 1 << 1,
      G_SIGNAL_MATCH_CLOSURE   = 1 << 2,
      G_SIGNAL_MATCH_FUNC	   = 1 << 3,
      G_SIGNAL_MATCH_DATA	   = 1 << 4,
      G_SIGNAL_MATCH_UNBLOCKED = 1 << 5
    } GSignalMatchType;

The match types specify what `g_signal_handlers_block_matched()`, `g_signal_handlers_unblock_matched()` and `g_signal_handlers_disconnect_matched()` match signals by.

`G_SIGNAL_MATCH_ID` | The signal id must be equal.
`G_SIGNAL_MATCH_DETAIL` | The signal detail be equal.
`G_SIGNAL_MATCH_CLOSURE` | The closure must be the same.
`G_SIGNAL_MATCH_FUNC` | The C closure callback must be the same.
`G_SIGNAL_MATCH_DATA` | The closure data must be the same.
`G_SIGNAL_MATCH_UNBLOCKED` | Only unblocked signals may matched.

### GSignalQuery

    typedef struct {
      guint		signal_id;
      const gchar  *signal_name;
      GType		itype;
      GSignalFlags	signal_flags;
      GType		return_type; /* mangled with G_SIGNAL_TYPE_STATIC_SCOPE flag */
      guint		n_params;
      const GType  *param_types; /* mangled with G_SIGNAL_TYPE_STATIC_SCOPE flag */
    } GSignalQuery;

A structure holding in-depth information for a specific signal. It is filled in by the `g_signal_query()` function.

guint `signal_id`; | The signal id of the signal being queried, or 0 if the signal to be queried was unknown.
const gchar *`signal_name`; | The signal name.
GType `itype`; | The interface/instance type that this signal can be emitted for.
GSignalFlags `signal_flags`; | The signal flags as passed in to `g_signal_new()`.
GType `return_type`; | The return type for user callbacks.
guint `n_params`; | The number of parameters that user callbacks take.

const GType *`param_types`;

The individual parameter types for user callbacks, note that the effective callback signature is:

     @return_type callback (gpointer     data1,
     [param_types param_names,]
     gpointer     data2);

### G_SIGNAL_TYPE_STATIC_SCOPE

    #define	G_SIGNAL_TYPE_STATIC_SCOPE (G_TYPE_FLAG_RESERVED_ID_BIT)

This macro flags signal argument types for which the signal system may assume that instances thereof remain persistent across all signal emissions they are used in. This is only useful for non ref-counted, value-copy types.

To flag a signal argument in this way, add `| G_SIGNAL_TYPE_STATIC_SCOPE` to the corresponding argument of `g_signal_new()`.

    g_signal_new ("size_request",
      G_TYPE_FROM_CLASS (gobject_class),
    	 G_SIGNAL_RUN_FIRST,
    	 G_STRUCT_OFFSET (GtkWidgetClass, size_request),
    	 NULL, NULL,
    	 _gtk_marshal_VOID__BOXED,
    	 G_TYPE_NONE, 1,
    	 GTK_TYPE_REQUISITION | G_SIGNAL_TYPE_STATIC_SCOPE);

### G_SIGNAL_MATCH_MASK

    #define G_SIGNAL_MATCH_MASK  0x3f

A mask for all GSignalMatchType bits.

### G_SIGNAL_FLAGS_MASK

    #define G_SIGNAL_FLAGS_MASK  0x7f

A mask for all GSignalFlags bits.

### g_signal_new ()

    guint               g_signal_new                        (const gchar *signal_name,
                                                             GType itype,
                                                             GSignalFlags signal_flags,
                                                             guint class_offset,
                                                             GSignalAccumulator accumulator,
                                                             gpointer accu_data,
                                                             GSignalCMarshaller c_marshaller,
                                                             GType return_type,
                                                             guint n_params,
                                                             ...);

Creates a new signal. (This is usually done in the class initializer.)

A signal name consists of segments consisting of ASCII letters and digits, separated by either the '-' or '_' character. The first character of a signal name must be a letter. Names which violate these rules lead to undefined behaviour of the GSignal system.

When registering a signal and looking up a signal, either separator can be used, but they cannot be mixed.

`signal_name` : | the name for the signal
`itype` : | the type this signal pertains to. It will also pertain to types which are derived from this type.
`signal_flags` : | a combination of GSignalFlags specifying detail of when the default handler is to be invoked. You should at least specify `G_SIGNAL_RUN_FIRST` or `G_SIGNAL_RUN_LAST`.
`class_offset` : | The offset of the function pointer in the class structure for this type. Used to invoke a class method generically. Pass 0 to not associate a class method with this signal.
`accumulator` : | the accumulator for this signal; may be `NULL`.
`accu_data` : | user data for the `accumulator`.
`c_marshaller` : | the function to translate arrays of parameter values to signal emissions into C language callback invocations.
`return_type` : | the type of return value, or G_TYPE_NONE for a signal without a return value.
`n_params` : | the number of parameter types to follow.
`...` : | a list of types, one for each parameter.
Returns : | the signal id

### g_signal_newv ()

    guint               g_signal_newv                       (const gchar *signal_name,
                                                             GType itype,
                                                             GSignalFlags signal_flags,
                                                             GClosure *class_closure,
                                                             GSignalAccumulator accumulator,
                                                             gpointer accu_data,
                                                             GSignalCMarshaller c_marshaller,
                                                             GType return_type,
                                                             guint n_params,
                                                             GType *param_types);

Creates a new signal. (This is usually done in the class initializer.)

See `g_signal_new()` for details on allowed signal names.

`signal_name` : | the name for the signal
`itype` : | the type this signal pertains to. It will also pertain to types which are derived from this type.
`signal_flags` : | a combination of GSignalFlags specifying detail of when the default handler is to be invoked. You should at least specify `G_SIGNAL_RUN_FIRST` or `G_SIGNAL_RUN_LAST`.
`class_closure` : | The closure to invoke on signal emission; may be `NULL`.
`accumulator` : | the accumulator for this signal; may be `NULL`.
`accu_data` : | user data for the `accumulator`.
`c_marshaller` : | the function to translate arrays of parameter values to signal emissions into C language callback invocations.
`return_type` : | the type of return value, or G_TYPE_NONE for a signal without a return value.
`n_params` : | the length of `param_types`.
`param_types` : | an array types, one for each parameter.
Returns : | the signal id

### g_signal_new_valist ()

    guint               g_signal_new_valist                 (const gchar *signal_name,
                                                             GType itype,
                                                             GSignalFlags signal_flags,
                                                             GClosure *class_closure,
                                                             GSignalAccumulator accumulator,
                                                             gpointer accu_data,
                                                             GSignalCMarshaller c_marshaller,
                                                             GType return_type,
                                                             guint n_params,
                                                             va_list args);

Creates a new signal. (This is usually done in the class initializer.)

See `g_signal_new()` for details on allowed signal names.

`signal_name` : | the name for the signal
`itype` : | the type this signal pertains to. It will also pertain to types which are derived from this type.
`signal_flags` : | a combination of GSignalFlags specifying detail of when the default handler is to be invoked. You should at least specify `G_SIGNAL_RUN_FIRST` or `G_SIGNAL_RUN_LAST`.
`class_closure` : | The closure to invoke on signal emission; may be `NULL`.
`accumulator` : | the accumulator for this signal; may be `NULL`.
`accu_data` : | user data for the `accumulator`.
`c_marshaller` : | the function to translate arrays of parameter values to signal emissions into C language callback invocations.
`return_type` : | the type of return value, or G_TYPE_NONE for a signal without a return value.
`n_params` : | the number of parameter types in `args`.
`args` : | va_list of GType, one for each parameter.
Returns : | the signal id

### g_signal_query ()

    void                g_signal_query                      (guint signal_id,
                                                             GSignalQuery *query);

Queries the signal system for in-depth information about a specific signal. This function will fill in a user-provided structure to hold signal-specific information. If an invalid signal id is passed in, the `signal_id` member of the GSignalQuery is 0. All members filled into the GSignalQuery structure should be considered constant and have to be left untouched.

`signal_id` : | The signal id of the signal to query information for.
`query` : | A user provided structure that is filled in with constant values upon success.

### g_signal_lookup ()

    guint               g_signal_lookup                     (const gchar *name,
                                                             GType itype);

Given the name of the signal and the type of object it connects to, gets the signal's identifying integer. Emitting the signal by number is somewhat faster than using the name each time.

Also tries the ancestors of the given type.

See `g_signal_new()` for details on allowed signal names.

`name` : | the signal's name.
`itype` : | the type that the signal operates on.
Returns : | the signal's identifying number, or 0 if no signal was found.

### g_signal_name ()

    const gchar*        g_signal_name                       (guint signal_id);

Given the signal's identifier, finds its name.

Two different signals may have the same name, if they have differing types.

`signal_id` : | the signal's identifying number.
Returns : | the signal name, or `NULL` if the signal number was invalid.

### g_signal_list_ids ()

    guint*              g_signal_list_ids                   (GType itype,
                                                             guint *n_ids);

Lists the signals by id that a certain instance or interface type created. Further information about the signals can be acquired through `g_signal_query()`.

`itype` : | Instance or interface type.
`n_ids` : | Location to store the number of signal ids for `itype`.
Returns : | Newly allocated array of signal IDs.

### g_signal_emit ()

    void                g_signal_emit                       (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             ...);

Emits a signal.

Note that `g_signal_emit()` resets the return value to the default if no handlers are connected, in contrast to `g_signal_emitv()`.

`instance` : | the instance the signal is being emitted on.
`signal_id` : | the signal id
`detail` : | the detail
`...` : | parameters to be passed to the signal, followed by a location for the return value. If the return type of the signal is G_TYPE_NONE, the return value location can be omitted.

### g_signal_emit_by_name ()

    void                g_signal_emit_by_name               (gpointer instance,
                                                             const gchar *detailed_signal,
                                                             ...);

Emits a signal.

Note that `g_signal_emit_by_name()` resets the return value to the default if no handlers are connected, in contrast to `g_signal_emitv()`.

`instance` : | the instance the signal is being emitted on.
`detailed_signal` : | a string of the form "signal-name::detail".
`...` : | parameters to be passed to the signal, followed by a location for the return value. If the return type of the signal is G_TYPE_NONE, the return value location can be omitted.

### g_signal_emitv ()

    void                g_signal_emitv                      (const GValue *instance_and_params,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GValue *return_value);

Emits a signal.

Note that `g_signal_emitv()` doesn't change `return_value` if no handlers are connected, in contrast to `g_signal_emit()` and `g_signal_emit_valist()`.

`instance_and_params` : | argument list for the signal emission. The first element in the array is a GValue for the instance the signal is being emitted on. The rest are any arguments to be passed to the signal.
`signal_id` : | the signal id
`detail` : | the detail
`return_value` : | Location to store the return value of the signal emission.

### g_signal_emit_valist ()

    void                g_signal_emit_valist                (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             va_list var_args);

Emits a signal.

Note that `g_signal_emit_valist()` resets the return value to the default if no handlers are connected, in contrast to `g_signal_emitv()`.

`instance` : | the instance the signal is being emitted on.
`signal_id` : | the signal id
`detail` : | the detail
`var_args` : | a list of parameters to be passed to the signal, followed by a location for the return value. If the return type of the signal is G_TYPE_NONE, the return value location can be omitted.

### g_signal_connect()

    #define             g_signal_connect(instance, detailed_signal, c_handler, data)

Connects a GCallback function to a signal for a particular object.

The handler will be called before the default handler of the signal.

`instance` : | the instance to connect to.
`detailed_signal` : | a string of the form "signal-name::detail".
`c_handler` : | the GCallback to connect.
`data` : | data to pass to `c_handler` calls.

### g_signal_connect_after()

    #define             g_signal_connect_after(instance, detailed_signal, c_handler, data)

Connects a GCallback function to a signal for a particular object.

The handler will be called after the default handler of the signal.

`instance` : | the instance to connect to.
`detailed_signal` : | a string of the form "signal-name::detail".
`c_handler` : | the GCallback to connect.
`data` : | data to pass to `c_handler` calls.

### g_signal_connect_swapped()

    #define             g_signal_connect_swapped(instance, detailed_signal, c_handler, data)

Connects a GCallback function to a signal for a particular object.

The instance on which the signal is emitted and `data` will be swapped when calling the handler.

`instance` : | the instance to connect to.
`detailed_signal` : | a string of the form "signal-name::detail".
`c_handler` : | the GCallback to connect.
`data` : | data to pass to `c_handler` calls.

### g_signal_connect_object ()

    gulong              g_signal_connect_object             (gpointer instance,
                                                             const gchar *detailed_signal,
                                                             GCallback c_handler,
                                                             gpointer gobject,
                                                             GConnectFlags connect_flags);

This is similar to `g_signal_connect_data()`, but uses a closure which ensures that the `gobject` stays alive during the call to `c_handler` by temporarily adding a reference count to `gobject`.

Note that there is a bug in GObject that makes this function much less useful than it might seem otherwise. Once `gobject` is disposed, the callback will no longer be called, but, the signal handler is not currently disconnected. If the `instance` is itself being freed at the same time than this doesn't matter, since the signal will automatically be removed, but if `instance` persists, then the signal handler will leak. You should not remove the signal yourself because in a future versions of GObject, the handler will automatically be disconnected.

It's possible to work around this problem in a way that will continue to work with future versions of GObject by checking that the signal handler is still connected before disconnected it:

     if (g_signal_handler_is_connected (instance, id))
       g_signal_handler_disconnect (instance, id);

`instance` : | the instance to connect to.
`detailed_signal` : | a string of the form "signal-name::detail".
`c_handler` : | the GCallback to connect.
`gobject` : | the object to pass as data to `c_handler`.
`connect_flags` : | a combination of GConnnectFlags.
Returns : | the handler id.

### enum GConnectFlags

    typedef enum
    {
      G_CONNECT_AFTER	= 1 << 0,
      G_CONNECT_SWAPPED	= 1 << 1
    } GConnectFlags;

The connection flags are used to specify the behaviour of a signal's connection.

`G_CONNECT_AFTER` | whether the handler should be called before or after the default handler of the signal.
`G_CONNECT_SWAPPED` | whether the instance and data should be swapped when calling the handler.

### g_signal_connect_data ()

    gulong              g_signal_connect_data               (gpointer instance,
                                                             const gchar *detailed_signal,
                                                             GCallback c_handler,
                                                             gpointer data,
                                                             GClosureNotify destroy_data,
                                                             GConnectFlags connect_flags);

Connects a GCallback function to a signal for a particular object. Similar to `g_signal_connect()`, but allows to provide a GClosureNotify for the data which will be called when the signal handler is disconnected and no longer used. Specify `connect_flags` if you need `...`_after()`` or `...`_swapped()`` variants of this function.

`instance` : | the instance to connect to.
`detailed_signal` : | a string of the form "signal-name::detail".
`c_handler` : | the GCallback to connect.
`data` : | data to pass to `c_handler` calls.
`destroy_data` : | a GClosureNotify for `data`.
`connect_flags` : | a combination of GConnectFlags.
Returns : | the handler id

### g_signal_connect_closure ()

    gulong              g_signal_connect_closure            (gpointer instance,
                                                             const gchar *detailed_signal,
                                                             GClosure *closure,
                                                             gboolean after);

Connects a closure to a signal for a particular object.

`instance` : | the instance to connect to.
`detailed_signal` : | a string of the form "signal-name::detail".
`closure` : | the closure to connect.
`after` : | whether the handler should be called before or after the default handler of the signal.
Returns : | the handler id

### g_signal_connect_closure_by_id ()

    gulong              g_signal_connect_closure_by_id      (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gboolean after);

Connects a closure to a signal for a particular object.

`instance` : | the instance to connect to.
`signal_id` : | the id of the signal.
`detail` : | the detail.
`closure` : | the closure to connect.
`after` : | whether the handler should be called before or after the default handler of the signal.
Returns : | the handler id

### g_signal_handler_block ()

    void                g_signal_handler_block              (gpointer instance,
                                                             gulong handler_id);

Blocks a handler of an instance so it will not be called during any signal emissions unless it is unblocked again. Thus "blocking" a signal handler means to temporarily deactive it, a signal handler has to be unblocked exactly the same amount of times it has been blocked before to become active again.

The `handler_id` has to be a valid signal handler id, connected to a signal of `instance`.

`instance` : | The instance to block the signal handler of.
`handler_id` : | Handler id of the handler to be blocked.

### g_signal_handler_unblock ()

    void                g_signal_handler_unblock            (gpointer instance,
                                                             gulong handler_id);

Undoes the effect of a previous `g_signal_handler_block()` call. A blocked handler is skipped during signal emissions and will not be invoked, unblocking it (for exactly the amount of times it has been blocked before) reverts its "blocked" state, so the handler will be recognized by the signal system and is called upon future or currently ongoing signal emissions (since the order in which handlers are called during signal emissions is deterministic, whether the unblocked handler in question is called as part of a currently ongoing emission depends on how far that emission has proceeded yet).

The `handler_id` has to be a valid id of a signal handler that is connected to a signal of `instance` and is currently blocked.

`instance` : | The instance to unblock the signal handler of.
`handler_id` : | Handler id of the handler to be unblocked.

### g_signal_handler_disconnect ()

    void                g_signal_handler_disconnect         (gpointer instance,
                                                             gulong handler_id);

Disconnects a handler from an instance so it will not be called during any future or currently ongoing emissions of the signal it has been connected to. The `handler_id` becomes invalid and may be reused.

The `handler_id` has to be a valid signal handler id, connected to a signal of `instance`.

`instance` : | The instance to remove the signal handler from.
`handler_id` : | Handler id of the handler to be disconnected.

### g_signal_handler_find ()

    gulong              g_signal_handler_find               (gpointer instance,
                                                             GSignalMatchType mask,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gpointer func,
                                                             gpointer data);

Finds the first signal handler that matches certain selection criteria. The criteria mask is passed as an OR-ed combination of GSignalMatchType flags, and the criteria values are passed as arguments. The match `mask` has to be non-0 for successful matches. If no handler was found, 0 is returned.

`instance` : | The instance owning the signal handler to be found.
`mask` : | Mask indicating which of `signal_id`, `detail`, `closure`, `func` and/or `data` the handler has to match.
`signal_id` : | Signal the handler has to be connected to.
`detail` : | Signal detail the handler has to be connected to.
`closure` : | The closure the handler will invoke.
`func` : | The C closure callback of the handler (useless for non-C closures).
`data` : | The closure data of the handler's closure.
Returns : | A valid non-0 signal handler id for a successful match.

### g_signal_handlers_block_matched ()

    guint               g_signal_handlers_block_matched     (gpointer instance,
                                                             GSignalMatchType mask,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gpointer func,
                                                             gpointer data);

Blocks all handlers on an instance that match a certain selection criteria. The criteria mask is passed as an OR-ed combination of GSignalMatchType flags, and the criteria values are passed as arguments. Passing at least one of the `G_SIGNAL_MATCH_CLOSURE`, `G_SIGNAL_MATCH_FUNC` or `G_SIGNAL_MATCH_DATA` match flags is required for successful matches. If no handlers were found, 0 is returned, the number of blocked handlers otherwise.

`instance` : | The instance to block handlers from.
`mask` : | Mask indicating which of `signal_id`, `detail`, `closure`, `func` and/or `data` the handlers have to match.
`signal_id` : | Signal the handlers have to be connected to.
`detail` : | Signal detail the handlers have to be connected to.
`closure` : | The closure the handlers will invoke.
`func` : | The C closure callback of the handlers (useless for non-C closures).
`data` : | The closure data of the handlers' closures.
Returns : | The number of handlers that matched.

### g_signal_handlers_unblock_matched ()

    guint               g_signal_handlers_unblock_matched   (gpointer instance,
                                                             GSignalMatchType mask,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gpointer func,
                                                             gpointer data);

Unblocks all handlers on an instance that match a certain selection criteria. The criteria mask is passed as an OR-ed combination of GSignalMatchType flags, and the criteria values are passed as arguments. Passing at least one of the `G_SIGNAL_MATCH_CLOSURE`, `G_SIGNAL_MATCH_FUNC` or `G_SIGNAL_MATCH_DATA` match flags is required for successful matches. If no handlers were found, 0 is returned, the number of unblocked handlers otherwise. The match criteria should not apply to any handlers that are not currently blocked.

`instance` : | The instance to unblock handlers from.
`mask` : | Mask indicating which of `signal_id`, `detail`, `closure`, `func` and/or `data` the handlers have to match.
`signal_id` : | Signal the handlers have to be connected to.
`detail` : | Signal detail the handlers have to be connected to.
`closure` : | The closure the handlers will invoke.
`func` : | The C closure callback of the handlers (useless for non-C closures).
`data` : | The closure data of the handlers' closures.
Returns : | The number of handlers that matched.

### g_signal_handlers_disconnect_matched ()

    guint               g_signal_handlers_disconnect_matched
                                                            (gpointer instance,
                                                             GSignalMatchType mask,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             GClosure *closure,
                                                             gpointer func,
                                                             gpointer data);

Disconnects all handlers on an instance that match a certain selection criteria. The criteria mask is passed as an OR-ed combination of GSignalMatchType flags, and the criteria values are passed as arguments. Passing at least one of the `G_SIGNAL_MATCH_CLOSURE`, `G_SIGNAL_MATCH_FUNC` or `G_SIGNAL_MATCH_DATA` match flags is required for successful matches. If no handlers were found, 0 is returned, the number of disconnected handlers otherwise.

`instance` : | The instance to remove handlers from.
`mask` : | Mask indicating which of `signal_id`, `detail`, `closure`, `func` and/or `data` the handlers have to match.
`signal_id` : | Signal the handlers have to be connected to.
`detail` : | Signal detail the handlers have to be connected to.
`closure` : | The closure the handlers will invoke.
`func` : | The C closure callback of the handlers (useless for non-C closures).
`data` : | The closure data of the handlers' closures.
Returns : | The number of handlers that matched.

### g_signal_handler_is_connected ()

    gboolean            g_signal_handler_is_connected       (gpointer instance,
                                                             gulong handler_id);

Returns whether `handler_id` is the id of a handler connected to `instance`.

`instance` : | The instance where a signal handler is sought.
`handler_id` : | the handler id.
Returns : | whether `handler_id` identifies a handler connected to `instance`.

### g_signal_handlers_block_by_func()

    #define             g_signal_handlers_block_by_func(instance, func, data)

Blocks all handlers on an instance that match `func` and `data`.

`instance` : | The instance to block handlers from.
`func` : | The C closure callback of the handlers (useless for non-C closures).
`data` : | The closure data of the handlers' closures.

### g_signal_handlers_unblock_by_func()

    #define             g_signal_handlers_unblock_by_func(instance, func, data)

Unblocks all handlers on an instance that match `func` and `data`.

`instance` : | The instance to unblock handlers from.
`func` : | The C closure callback of the handlers (useless for non-C closures).
`data` : | The closure data of the handlers' closures.

### g_signal_handlers_disconnect_by_func()

    #define             g_signal_handlers_disconnect_by_func(instance, func, data)

Disconnects all handlers on an instance that match `func` and `data`.

`instance` : | The instance to remove handlers from.
`func` : | The C closure callback of the handlers (useless for non-C closures).
`data` : | The closure data of the handlers' closures.

### g_signal_has_handler_pending ()

    gboolean            g_signal_has_handler_pending        (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail,
                                                             gboolean may_be_blocked);

Returns whether there are any handlers connected to `instance` for the given signal id and detail.

One example of when you might use this is when the arguments to the signal are difficult to compute. A class implementor may opt to not emit the signal if no one is attached anyway, thus saving the cost of building the arguments.

`instance` : | the object whose signal handlers are sought.
`signal_id` : | the signal id.
`detail` : | the detail.
`may_be_blocked` : | whether blocked handlers should count as match.
Returns : | `TRUE` if a handler is connected to the signal, `FALSE` otherwise.

### g_signal_stop_emission ()

    void                g_signal_stop_emission              (gpointer instance,
                                                             guint signal_id,
                                                             GQuark detail);

Stops a signal's current emission.

This will prevent the default method from running, if the signal was `G_SIGNAL_RUN_LAST` and you connected normally (i.e. without the "after" flag).

Prints a warning if used on a signal which isn't being emitted.

`instance` : | the object whose signal handlers you wish to stop.
`signal_id` : | the signal identifier, as returned by `g_signal_lookup()`.
`detail` : | the detail which the signal was emitted with.

### g_signal_stop_emission_by_name ()

    void                g_signal_stop_emission_by_name      (gpointer instance,
                                                             const gchar *detailed_signal);

Stops a signal's current emission.

This is just like `g_signal_stop_emission()` except it will look up the signal id for you.

`instance` : | the object whose signal handlers you wish to stop.
`detailed_signal` : | a string of the form "signal-name::detail".

### g_signal_override_class_closure ()

    void                g_signal_override_class_closure     (guint signal_id,
                                                             GType instance_type,
                                                             GClosure *class_closure);

Overrides the class closure (i.e. the default handler) for the given signal for emissions on instances of `instance_type`. `instance_type` must be derived from the type to which the signal belongs.

See `g_signal_chain_from_overridden()` and `g_signal_chain_from_overridden_handler()` for how to chain up to the parent class closure from inside the overridden one.

`signal_id` : | the signal id
`instance_type` : | the instance type on which to override the class closure for the signal.
`class_closure` : | the closure.

### g_signal_chain_from_overridden ()

    void                g_signal_chain_from_overridden      (const GValue *instance_and_params,
                                                             GValue *return_value);

Calls the original class closure of a signal. This function should only be called from an overridden class closure; see `g_signal_override_class_closure()` and `g_signal_override_class_handler()`.

`instance_and_params` : | the argument list of the signal emission. The first element in the array is a GValue for the instance the signal is being emitted on. The rest are any arguments to be passed to the signal.
`return_value` : | Location for the return value.

### g_signal_new_class_handler ()

    guint               g_signal_new_class_handler          (const gchar *signal_name,
                                                             GType itype,
                                                             GSignalFlags signal_flags,
                                                             GCallback class_handler,
                                                             GSignalAccumulator accumulator,
                                                             gpointer accu_data,
                                                             GSignalCMarshaller c_marshaller,
                                                             GType return_type,
                                                             guint n_params,
                                                             ...);

Creates a new signal. (This is usually done in the class initializer.)

This is a variant of `g_signal_new()` that takes a C callback instead off a class offset for the signal's class handler. This function doesn't need a function pointer exposed in the class structure of an object definition, instead the function pointer is passed directly and can be overriden by derived classes with `g_signal_override_class_closure()` or `g_signal_override_class_handler()`and chained to with `g_signal_chain_from_overridden()` or `g_signal_chain_from_overridden_handler()`.

See `g_signal_new()` for information about signal names.

`signal_name` : | the name for the signal
`itype` : | the type this signal pertains to. It will also pertain to types which are derived from this type.
`signal_flags` : | a combination of GSignalFlags specifying detail of when the default handler is to be invoked. You should at least specify `G_SIGNAL_RUN_FIRST` or `G_SIGNAL_RUN_LAST`.
`class_handler` : | a GCallback which acts as class implementation of this signal. Used to invoke a class method generically. Pass `NULL` to not associate a class method with this signal.
`accumulator` : | the accumulator for this signal; may be `NULL`.
`accu_data` : | user data for the `accumulator`.
`c_marshaller` : | the function to translate arrays of parameter values to signal emissions into C language callback invocations.
`return_type` : | the type of return value, or G_TYPE_NONE for a signal without a return value.
`n_params` : | the number of parameter types to follow.
`...` : | a list of types, one for each parameter.
Returns : | the signal id

Since 2.18

### g_signal_override_class_handler ()

    void                g_signal_override_class_handler     (const gchar *signal_name,
                                                             GType instance_type,
                                                             GCallback class_handler);

Overrides the class closure (i.e. the default handler) for the given signal for emissions on instances of `instance_type` with callabck `class_handler`. `instance_type` must be derived from the type to which the signal belongs.

See `g_signal_chain_from_overridden()` and `g_signal_chain_from_overridden_handler()` for how to chain up to the parent class closure from inside the overridden one.

`signal_name` : | the name for the signal
`instance_type` : | the instance type on which to override the class handler for the signal.
`class_handler` : | the handler.

Since 2.18

### g_signal_chain_from_overridden_handler ()

    void                g_signal_chain_from_overridden_handler
                                                            (gpointer instance,
                                                             ...);

Calls the original class closure of a signal. This function should only be called from an overridden class closure; see `g_signal_override_class_closure()` and `g_signal_override_class_handler()`.

`instance` : | the instance the signal is being emitted on.
`...` : | parameters to be passed to the parent class closure, followed by a location for the return value. If the return type of the signal is G_TYPE_NONE, the return value location can be omitted.

Since 2.18

### g_signal_add_emission_hook ()

    gulong              g_signal_add_emission_hook          (guint signal_id,
                                                             GQuark detail,
                                                             GSignalEmissionHook hook_func,
                                                             gpointer hook_data,
                                                             GDestroyNotify data_destroy);

Adds an emission hook for a signal, which will get called for any emission of that signal, independent of the instance. This is possible only for signals which don't have G_SIGNAL_NO_HOOKS flag set.

`signal_id` : | the signal identifier, as returned by `g_signal_lookup()`.
`detail` : | the detail on which to call the hook.
`hook_func` : | a GSignalEmissionHook function.
`hook_data` : | user data for `hook_func`.
`data_destroy` : | a GDestroyNotify for `hook_data`.
Returns : | the hook id, for later use with `g_signal_remove_emission_hook()`.

### g_signal_remove_emission_hook ()

    void                g_signal_remove_emission_hook       (guint signal_id,
                                                             gulong hook_id);

Deletes an emission hook.

`signal_id` : | the id of the signal
`hook_id` : | the id of the emission hook, as returned by `g_signal_add_emission_hook()`

### g_signal_parse_name ()

    gboolean            g_signal_parse_name                 (const gchar *detailed_signal,
                                                             GType itype,
                                                             guint *signal_id_p,
                                                             GQuark *detail_p,
                                                             gboolean force_detail_quark);

Internal function to parse a signal name into its `signal_id` and `detail` quark.

`detailed_signal` : | a string of the form "signal-name::detail".
`itype` : | The interface/instance type that introduced "signal-name".
`signal_id_p` : | Location to store the signal id.
`detail_p` : | Location to store the detail quark.
`force_detail_quark` : | `TRUE` forces creation of a GQuark for the detail.
Returns : | Whether the signal name could successfully be parsed and `signal_id_p` and `detail_p` contain valid return values.

### g_signal_get_invocation_hint ()

    GSignalInvocationHint* g_signal_get_invocation_hint     (gpointer instance);

Returns the invocation hint of the innermost signal emission of instance.

`instance` : | the instance to query
Returns : | the invocation hint of the innermost signal emission.

### g_signal_type_cclosure_new ()

    GClosure*           g_signal_type_cclosure_new          (GType itype,
                                                             guint struct_offset);

Creates a new closure which invokes the function found at the offset `struct_offset` in the class structure of the interface or classed type identified by `itype`.

`itype` : | the GType identifier of an interface or classed type
`struct_offset` : | the offset of the member function of `itype`'s class structure which is to be invoked by the new closure
Returns : | a new GCClosure

### g_signal_accumulator_true_handled ()

    gboolean            g_signal_accumulator_true_handled   (GSignalInvocationHint *ihint,
                                                             GValue *return_accu,
                                                             const GValue *handler_return,
                                                             gpointer dummy);

A predefined GSignalAccumulator for signals that return a boolean values. The behavior that this accumulator gives is that a return of `TRUE` stops the signal emission: no further callbacks will be invoked, while a return of `FALSE` allows the emission to coninue. The idea here is that a `TRUE` return indicates that the callback handled the signal, and no further handling is needed.

`ihint` : | standard GSignalAccumulator parameter
`return_accu` : | standard GSignalAccumulator parameter
`handler_return` : | standard GSignalAccumulator parameter
`dummy` : | standard GSignalAccumulator parameter
Returns : | standard GSignalAccumulator result

Since 2.4

[12] Although signals can deal with any kind of instantiatable type, i'm referring to those types as "object types" in the following, simply because that is the context most users will encounter signals in.