glib/docs/reference/gobject/tmpl/signals.sgml

<!-- ##### SECTION Title ##### -->
Signals

<!-- ##### SECTION Short_Description ##### -->
Signals provide a means for customization of object behaviour and are used
as general purpose notification mechanism.

<!-- ##### SECTION Long_Description ##### -->
<para>
The basic concept of the signal system is that of the <emphasis>emission</emphasis>
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
	<footnote><para>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.
	</para></footnote>
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.
</para>
<para>
A signal emission consists of five stages, unless prematurely stopped:
<variablelist>
  <varlistentry><term></term><listitem><para>
	1 - Invocation of the object method handler for %G_SIGNAL_RUN_FIRST signals
  </para></listitem></varlistentry>
  <varlistentry><term></term><listitem><para>
	2 - Invocation of normal user-provided signal handlers (<emphasis>after</emphasis> flag %FALSE)
  </para></listitem></varlistentry>
  <varlistentry><term></term><listitem><para>
	3 - Invocation of the object method handler for %G_SIGNAL_RUN_LAST signals
  </para></listitem></varlistentry>
  <varlistentry><term></term><listitem><para>
	4 - Invocation of user provided signal handlers, connected with an <emphasis>after</emphasis> flag of %TRUE
  </para></listitem></varlistentry>
  <varlistentry><term></term><listitem><para>
	5 - Invocation of the object method handler for %G_SIGNAL_RUN_CLEANUP signals
  </para></listitem></varlistentry>
</variablelist>
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 <emphasis>blocked</emphasis>, 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.
</para>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### STRUCT GSignalInvocationHint ##### -->
<para>
The #GSignalInvocationHint structure is used to pass on additional information
to callbacks during a signal emission.
</para>

@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.

<!-- ##### USER_FUNCTION GSignalAccumulator ##### -->
<para>
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.
</para>

@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.
<!-- # Unused Parameters # -->
@return_value: 	The return value of the most recent callback function.


<!-- ##### TYPEDEF GSignalCMarshaller ##### -->
<para>
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.
</para>


<!-- ##### USER_FUNCTION GSignalEmissionHook ##### -->
<para>

</para>

@ihint: 
@n_param_values: 
@param_values: 
@data: 
@Returns: 
<!-- # Unused Parameters # -->
@signal_id: 
@n_values: 
@values: 


<!-- ##### ENUM GSignalFlags ##### -->
<para>
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.
</para>

@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.

<!-- ##### ENUM GSignalMatchType ##### -->
<para>

</para>

@G_SIGNAL_MATCH_ID: 
@G_SIGNAL_MATCH_DETAIL: 
@G_SIGNAL_MATCH_CLOSURE: 
@G_SIGNAL_MATCH_FUNC: 
@G_SIGNAL_MATCH_DATA: 
@G_SIGNAL_MATCH_UNBLOCKED: 

<!-- ##### STRUCT GSignalQuery ##### -->
<para>
A structure holding in-depth information for a specific signal. It is
filled in by the g_signal_query() function.
</para>

@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:
<programlisting>
@return_type callback (#gpointer     data1,
                      [#param_types param_names,]
                       #gpointer     data2);
</programlisting>

<!-- ##### MACRO G_SIGNAL_TYPE_STATIC_SCOPE ##### -->
<para>

</para>



<!-- ##### MACRO G_SIGNAL_MATCH_MASK ##### -->
<para>

</para>



<!-- ##### MACRO G_SIGNAL_FLAGS_MASK ##### -->
<para>

</para>



<!-- ##### FUNCTION g_signal_new ##### -->
<para>

</para>

@signal_name: 
@itype: 
@signal_flags: 
@class_offset: 
@accumulator: 
@accu_data: 
@c_marshaller: 
@return_type: 
@n_params: 
@Varargs: 
@Returns: 


<!-- ##### FUNCTION g_signal_newv ##### -->
<para>

</para>

@signal_name: 
@itype: 
@signal_flags: 
@class_closure: 
@accumulator: 
@accu_data: 
@c_marshaller: 
@return_type: 
@n_params: 
@param_types: 
@Returns: 


<!-- ##### FUNCTION g_signal_new_valist ##### -->
<para>

</para>

@signal_name: 
@itype: 
@signal_flags: 
@class_closure: 
@accumulator: 
@accu_data: 
@c_marshaller: 
@return_type: 
@n_params: 
@args: 
@Returns: 


<!-- ##### FUNCTION g_signal_query ##### -->
<para>
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.
</para>

@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.


<!-- ##### FUNCTION g_signal_lookup ##### -->
<para>

</para>

@name: 
@itype: 
@Returns: 


<!-- ##### FUNCTION g_signal_name ##### -->
<para>

</para>

@signal_id: 
@Returns: 


<!-- ##### FUNCTION g_signal_list_ids ##### -->
<para>
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().
</para>

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


<!-- ##### FUNCTION g_signal_emit ##### -->
<para>

</para>

@instance: 
@signal_id: 
@detail: 
@Varargs: 


<!-- ##### FUNCTION g_signal_emit_by_name ##### -->
<para>

</para>

@instance: 
@detailed_signal: 
@Varargs: 


<!-- ##### FUNCTION g_signal_emitv ##### -->
<para>

</para>

@instance_and_params: 
@signal_id: 
@detail: 
@return_value: 


<!-- ##### FUNCTION g_signal_emit_valist ##### -->
<para>

</para>

@instance: 
@signal_id: 
@detail: 
@var_args: 


<!-- ##### MACRO g_signal_connect ##### -->
<para>

</para>

@instance: 
@detailed_signal: 
@c_handler: 
@data: 


<!-- ##### MACRO g_signal_connect_after ##### -->
<para>

</para>

@instance: 
@detailed_signal: 
@c_handler: 
@data: 


<!-- ##### MACRO g_signal_connect_swapped ##### -->
<para>

</para>

@instance: 
@detailed_signal: 
@c_handler: 
@data: 


<!-- ##### FUNCTION g_signal_connect_object ##### -->
<para>

</para>

@instance: 
@detailed_signal: 
@c_handler: 
@gobject: 
@connect_flags: 
@Returns: 
<!-- # Unused Parameters # -->
@swapped: 
@after: 


<!-- ##### ENUM GConnectFlags ##### -->
<para>

</para>

@G_CONNECT_AFTER: 
@G_CONNECT_SWAPPED: 

<!-- ##### FUNCTION g_signal_connect_data ##### -->
<para>

</para>

@instance: 
@detailed_signal: 
@c_handler: 
@data: 
@destroy_data: 
@connect_flags: 
@Returns: 
<!-- # Unused Parameters # -->
@swapped: 
@after: 


<!-- ##### FUNCTION g_signal_connect_closure ##### -->
<para>

</para>

@instance: 
@detailed_signal: 
@closure: 
@after: 
@Returns: 
<!-- # Unused Parameters # -->
@signal_id: 
@detail: 


<!-- ##### FUNCTION g_signal_connect_closure_by_id ##### -->
<para>

</para>

@instance: 
@signal_id: 
@detail: 
@closure: 
@after: 
@Returns: 


<!-- ##### FUNCTION g_signal_handler_block ##### -->
<para>
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.
</para>

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


<!-- ##### FUNCTION g_signal_handler_unblock ##### -->
<para>
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.
</para>

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


<!-- ##### FUNCTION g_signal_handler_disconnect ##### -->
<para>
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.
</para>

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


<!-- ##### FUNCTION g_signal_handler_find ##### -->
<para>
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.
</para>

@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.


<!-- ##### FUNCTION g_signal_handlers_block_matched ##### -->
<para>
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.
</para>

@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.


<!-- ##### FUNCTION g_signal_handlers_unblock_matched ##### -->
<para>
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.
</para>

@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.


<!-- ##### FUNCTION g_signal_handlers_disconnect_matched ##### -->
<para>
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.
</para>

@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.


<!-- ##### FUNCTION g_signal_handler_is_connected ##### -->
<para>

</para>

@instance: 
@handler_id: 
@Returns: 


<!-- ##### MACRO g_signal_handlers_block_by_func ##### -->
<para>

</para>

@instance: 
@func: 
@data: 


<!-- ##### MACRO g_signal_handlers_unblock_by_func ##### -->
<para>

</para>

@instance: 
@func: 
@data: 


<!-- ##### MACRO g_signal_handlers_disconnect_by_func ##### -->
<para>

</para>

@instance: 
@func: 
@data: 


<!-- ##### FUNCTION g_signal_has_handler_pending ##### -->
<para>

</para>

@instance: 
@signal_id: 
@detail: 
@may_be_blocked: 
@Returns: 


<!-- ##### FUNCTION g_signal_stop_emission ##### -->
<para>

</para>

@instance: 
@signal_id: 
@detail: 


<!-- ##### FUNCTION g_signal_stop_emission_by_name ##### -->
<para>

</para>

@instance: 
@detailed_signal: 


<!-- ##### FUNCTION g_signal_override_class_closure ##### -->
<para>

</para>

@signal_id: 
@instance_type: 
@class_closure: 


<!-- ##### FUNCTION g_signal_chain_from_overridden ##### -->
<para>

</para>

@instance_and_params: 
@return_value: 
<!-- # Unused Parameters # -->
@signal_id: 


<!-- ##### FUNCTION g_signal_add_emission_hook ##### -->
<para>

</para>

@signal_id: 
@quark: 
@hook_func: 
@hook_data: 
@data_destroy: 
@Returns: 


<!-- ##### FUNCTION g_signal_remove_emission_hook ##### -->
<para>

</para>

@signal_id: 
@hook_id: 


<!-- ##### FUNCTION g_signal_parse_name ##### -->
<para>
Internal function to parse a signal names into its @signal_id
and @detail quark.
</para>

@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.


<!-- ##### FUNCTION g_signal_get_invocation_hint ##### -->
<para>

</para>

@instance: 
@Returns: 


<!-- ##### FUNCTION g_signal_handlers_destroy ##### -->
<para>

</para>

@instance: 


<!-- ##### FUNCTION g_signal_type_cclosure_new ##### -->
<para>

</para>

@itype: 
@struct_offset: 
@Returns: