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 availale 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 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 perfomed. The return value of signal emissions is then the value returned by the last callback. @ihint: Signal invokation hint, see @GSignalInvocationHint @return_accu: Accumulator to collect callback return values in, this is the return value of the current signal emission @return_value: The return value of the most recent callback function @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. @ihint: @n_param_values: @param_values: @Returns: @signal_id: @n_values: @values: @G_SIGNAL_RUN_FIRST: @G_SIGNAL_RUN_LAST: @G_SIGNAL_RUN_CLEANUP: @G_SIGNAL_NO_RECURSE: @G_SIGNAL_DETAILED: @G_SIGNAL_ACTION: @G_SIGNAL_NO_HOOKS: @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 querried, or 0 if the signal to be querried 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_closure: @accumulator: @c_marshaller: @return_type: @n_params: @param_types: @Returns: @instance_and_params: @signal_id: @detail: @return_value: @name: @itype: @Returns: @signal_id: @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 dignal 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. List the signals by id, that a certain instance or interface type created. Further information about the signals can be aquired 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: @closure: @after: @Returns: @instance: @mask: @signal_id: @detail: @closure: @func: @data: @Returns: @instance: @handler_id: @instance: @handler_id: @instance: @handler_id: @instance: @signal_id: @detail: @may_be_blocked: @Returns: @instance: @signal_id: @detail: @itype: @struct_offset: @Returns: @signal_id: @closure: @Returns: @signal_id: @hook_id: @instance: @itype: