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

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

<!-- ##### SECTION Short_Description ##### -->
A means for customization of object behaviour and a 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.


<!-- ##### 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>
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.
</para>
<para>
You may not attach these to signals created with the #G_SIGNAL_NO_HOOKS flag.
</para>

@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 ##### -->
<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" 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 ##### -->
<para>
The match types specify what g_signal_handlers_block_matched(),
g_signal_handlers_unblock_matched() and g_signal_handlers_disconnect_matched()
match signals by.
</para>

@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.

<!-- ##### 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>
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.
</para>
<para>
To flag a signal argument in this way, add 
<literal>| G_SIGNAL_TYPE_STATIC_SCOPE</literal> to the corresponding argument
of g_signal_new().
</para>
<informalexample>
<programlisting>
    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);
</programlisting>
</informalexample>



<!-- ##### MACRO G_SIGNAL_MATCH_MASK ##### -->
<para>
A mask for all #GSignalMatchType bits.
</para>



<!-- ##### MACRO G_SIGNAL_FLAGS_MASK ##### -->
<para>
A mask for all #GSignalFlags bits.
</para>



<!-- ##### FUNCTION g_signal_new ##### -->
<para>
Creates a new signal. (This is usually done in the class initializer.)
</para>
<para>
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. 
</para>
<para>
When registering a signal and looking up a signal, either separator can
be used, but they cannot be mixed. 
</para>

@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


<!-- ##### FUNCTION g_signal_newv ##### -->
<para>
Creates a new signal. (This is usually done in the class initializer.)
</para>
<para>
See g_signal_new() for details on allowed signal names.
</para>

@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


<!-- ##### FUNCTION g_signal_new_valist ##### -->
<para>
Creates a new signal. (This is usually done in the class initializer.)
</para>
<para>
See g_signal_new() for details on allowed signal names.
</para>

@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


<!-- ##### FUNCTION g_signal_query ##### -->
<para>
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.
</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>
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.
</para>
<para>
Also tries the ancestors of the given type.
</para>
<para>
See g_signal_new() for details on allowed signal names.
</para>

@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.


<!-- ##### FUNCTION g_signal_name ##### -->
<para>
Given the signal's identifier, finds its name.
</para>
<para>
Two different signals may have the same name, if they have differing types.
</para>

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


<!-- ##### FUNCTION g_signal_list_ids ##### -->
<para>
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().
</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>
Emits a signal. 
</para>
<para>
Note that g_signal_emit() resets the return value to the default
if no handlers are connected, in contrast to g_signal_emitv().
</para>

@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.


<!-- ##### FUNCTION g_signal_emit_by_name ##### -->
<para>
Emits a signal. 
</para>
<para>
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().
</para>

@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.


<!-- ##### FUNCTION g_signal_emitv ##### -->
<para>
Emits a signal. 
</para>
<para>
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().
</para>

@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.


<!-- ##### FUNCTION g_signal_emit_valist ##### -->
<para>
Emits a signal. 
</para>
<para>
Note that g_signal_emit_valist() resets the return value to the default
if no handlers are connected, in contrast to g_signal_emitv().
</para>

@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.


<!-- ##### MACRO g_signal_connect ##### -->
<para>
Connects a #GCallback function to a signal for a particular object.
</para>
<para>
The handler will be called before the default handler of the signal.
</para>

@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


<!-- ##### MACRO g_signal_connect_after ##### -->
<para>
Connects a #GCallback function to a signal for a particular object.
</para>
<para>
The handler will be called after the default handler of the signal.
</para>

@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


<!-- ##### MACRO g_signal_connect_swapped ##### -->
<para>
Connects a #GCallback function to a signal for a particular object.
</para>
<para>
The instance on which the signal is emitted and @data will be swapped when 
calling the handler.
</para>

@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


<!-- ##### FUNCTION g_signal_connect_object ##### -->
<para>
 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.
</para>
<para>
 Note that there this 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 <emphasis>not</emphasis> 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 <emphasis>will</emphasis> automatically
 be disconnected.
</para>
<para>
 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:
<informalexample><programlisting>
 if (g_signal_handler_is_connected (instance, id))
   g_signal_handler_disconnect (instance, id);
</programlisting></informalexample>
</para>

@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 ##### -->
<para>
The connection flags are used to specify the behaviour of a signal's 
connection.
</para>

@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.

<!-- ##### FUNCTION g_signal_connect_data ##### -->
<para>
Connects a #GCallback function to a signal for a particular object.
</para>

@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


<!-- ##### FUNCTION g_signal_connect_closure ##### -->
<para>
Connects a closure to a signal for a particular object.
</para>

@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


<!-- ##### FUNCTION g_signal_connect_closure_by_id ##### -->
<para>
Connects a closure to a signal for a particular object.
</para>

@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


<!-- ##### FUNCTION g_signal_handler_block ##### -->
<para>
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.
</para>
<para>
The @handler_id 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>
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).
</para>
<para>
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.
</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>
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.
</para>
<para>
The @handler_id 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>
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.
</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>
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>
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>
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>
Returns whether @handler_id is the id of a handler connected to @instance.
</para>

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


<!-- ##### MACRO g_signal_handlers_block_by_func ##### -->
<para>
Blocks all handlers on an instance that match @func and @data.
</para>

@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.


<!-- ##### MACRO g_signal_handlers_unblock_by_func ##### -->
<para>
Unblocks all handlers on an instance that match @func and @data.
</para>

@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.


<!-- ##### MACRO g_signal_handlers_disconnect_by_func ##### -->
<para>
Disconnects all handlers on an instance that match @func and @data.
</para>

@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.


<!-- ##### FUNCTION g_signal_has_handler_pending ##### -->
<para>
Returns whether there are any handlers connected to @instance for the
given signal id and detail.
</para>
<para>
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.
</para>

@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.


<!-- ##### FUNCTION g_signal_stop_emission ##### -->
<para>
Stops a signal's current emission.
</para>
<para>
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).
</para>
<para>
Prints a warning if used on a signal which isn't being emitted.
</para>

@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.


<!-- ##### FUNCTION g_signal_stop_emission_by_name ##### -->
<para>
Stops a signal's current emission.
</para>
<para>
This is just like g_signal_stop_emission() except it will look up the 
signal id for you.
</para>

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


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

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


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

@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.


<!-- ##### FUNCTION g_signal_add_emission_hook ##### -->
<para>
Adds an emission hook for a signal, which will get called for any emission
of that signal, independent of the instance.
</para>

@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().


<!-- ##### FUNCTION g_signal_remove_emission_hook ##### -->
<para>
Deletes an emission hook.
</para>

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


<!-- ##### FUNCTION g_signal_parse_name ##### -->
<para>
Internal function to parse a signal name 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 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.


<!-- ##### FUNCTION g_signal_get_invocation_hint ##### -->
<para>
Returns the invocation hint of the innermost signal emission of instance. 
</para>

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


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

@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


<!-- ##### FUNCTION g_signal_accumulator_true_handled ##### -->
<para>
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 invokced, while a return of %FALSE allows
the emission to coninue. The idea here is that a %TRUE return
indicates that the callback <emphasis>handled</emphasis> the signal,
and no further handling is needed.
</para>

@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