Signals Signals provide a means for customization of object behaviour and are used as 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. @return_value: The return value of the most recent callback function. 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. @ihint: @n_param_values: @param_values: @data: @Returns: @signal_id: @n_values: @values: 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. @G_SIGNAL_MATCH_ID: @G_SIGNAL_MATCH_DETAIL: @G_SIGNAL_MATCH_CLOSURE: @G_SIGNAL_MATCH_FUNC: @G_SIGNAL_MATCH_DATA: @G_SIGNAL_MATCH_UNBLOCKED: 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); @signal_name: @itype: @signal_flags: @class_offset: @accumulator: @accu_data: @c_marshaller: @return_type: @n_params: @Varargs: @Returns: @signal_name: @itype: @signal_flags: @class_closure: @accumulator: @accu_data: @c_marshaller: @return_type: @n_params: @param_types: @Returns: @signal_name: @itype: @signal_flags: @class_closure: @accumulator: @accu_data: @c_marshaller: @return_type: @n_params: @args: @Returns: Query 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. @name: @itype: @Returns: @signal_id: @Returns: List 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. @instance: @signal_id: @detail: @Varargs: @instance: @detailed_signal: @Varargs: @instance_and_params: @signal_id: @detail: @return_value: @instance: @signal_id: @detail: @var_args: @instance: @detailed_signal: @c_handler: @data: @instance: @detailed_signal: @c_handler: @data: @instance: @detailed_signal: @c_handler: @data: @instance: @detailed_signal: @c_handler: @gobject: @connect_flags: @Returns: @swapped: @after: @G_CONNECT_AFTER: @G_CONNECT_SWAPPED: @instance: @detailed_signal: @c_handler: @data: @destroy_data: @connect_flags: @Returns: @swapped: @after: @instance: @detailed_signal: @closure: @after: @Returns: @signal_id: @detail: @instance: @signal_id: @detail: @closure: @after: @Returns: g_signal_handler_block() 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 passed into g_signal_handler_block() 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() 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 passed into g_signal_handler_unblock() 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() 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 passed into g_signal_handler_disconnect() 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. Find 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. This function 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. This function 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. This function 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. @instance: @handler_id: @Returns: @instance: @func: @data: @instance: @func: @data: @instance: @func: @data: @instance: @signal_id: @detail: @may_be_blocked: @Returns: @instance: @signal_id: @detail: @instance: @detailed_signal: @signal_id: @quark: @hook_func: @hook_data: @data_destroy: @Returns: @signal_id: @hook_id: Internal function to parse a signal names 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 stroe 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. @instance: @itype: @struct_offset: @Returns: