Signals A means for customization of object behaviour and a general purpose notification mechanism 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 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. 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. The #GSignalInvocationHint structure is used to pass on additional information to callbacks during a signal emission. @signal_id: The signal id of the signal invoking the callback @detail: The detail passed on for this emission @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. 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: @data: @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. 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. 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). 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" appendixes 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 by third-party code generically callable object methods. @G_SIGNAL_NO_HOOKS: No emissions hooks are supported for this signal. 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. A structure holding in-depth information for a specific signal. It is filled in by the g_signal_query() function. @signal_id: The signal id of the signal being queried, or 0 if the signal to be queried was unknown. @signal_name: The signal name. @itype: The interface/instance type that this signal can be emitted for. @signal_flags: The signal flags as passed in to g_signal_new(). @return_type: The return type for user callbacks. @n_params: The number of parameters that user callbacks take. @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); 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); 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. @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. @Varargs: a list of types, one for each parameter. @Returns: the signal id 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. @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 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. @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 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. 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. 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. 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. 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 @Varargs: 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. 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". @Varargs: 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. 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. 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. 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. @Returns: the handler id 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. @Returns: the handler id 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. @Returns: the handler id This is similar to g_signal_connect_data(), but uses a closure which ensures that the object stays alive during the call to @c_handler. @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. 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. Connects a #GCallback function to a signal for a particular object. @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 #GDestroyNotify for @data. @connect_flags: a combination of #GConnectFlags. @Returns: the handler id 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 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 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. 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. 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. 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. 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 amount of handlers that got blocked. 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 amount of handlers that got unblocked. 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 amount of handlers that got disconnected. 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. 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. @Returns: The number of handlers that got blocked. 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. @Returns: The number of handlers that got unblocked. 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. @Returns: The number of handlers that got disconnected. 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. 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. 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". 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. @signal_id: the signal id @instance_type: the instance type on which to override the class closure for the signal. @class_closure: the closure. 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(). @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. Adds an emission hook for a signal, which will get called for any emission of that signal, independent of the instance. @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(). 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() 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. 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. @itype: @struct_offset: @Returns: