src/parsec/disk-image/parsec/parsec-benchmark/pkgs/libs/glib/src/docs/reference/gobject/html/signal.html - public/gem5-resources - Git at Google

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Signals</title>
 <meta name="generator" content="DocBook XSL Stylesheets V1.75.2">
 <link rel="home" href="index.html" title="GObject Reference Manual">
 <link rel="up" href="chapter-signal.html" title="The GObject messaging system">
 <link rel="prev" href="chapter-signal.html" title="The GObject messaging system">
 <link rel="next" href="rn01.html" title="API Reference">
 <meta name="generator" content="GTK-Doc V1.14 (XML mode)">
 <link rel="stylesheet" href="style.css" type="text/css">
 </head>
 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
 <table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="2"><tr valign="middle">
 <td><a accesskey="p" href="chapter-signal.html"><img src="left.png" width="24" height="24" border="0" alt="Prev"></a></td>
 <td><a accesskey="u" href="chapter-signal.html"><img src="up.png" width="24" height="24" border="0" alt="Up"></a></td>
 <td><a accesskey="h" href="index.html"><img src="home.png" width="24" height="24" border="0" alt="Home"></a></td>
 <th width="100%" align="center">GObject Reference Manual</th>
 <td><a accesskey="n" href="rn01.html"><img src="right.png" width="24" height="24" border="0" alt="Next"></a></td>
 </tr></table>
 <div class="sect1" title="Signals">
 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 <a name="signal"></a>Signals</h2></div></div></div>
 <p>
       GObject's signals have nothing to do with standard UNIX signals: they connect
       arbitrary application-specific events with any number of listeners.
       For example, in GTK+, every user event (keystroke or mouse move) is received
       from the X server and generates a GTK+ event under the form of a signal emission
       on a given object instance.
     </p>
 <p>
       Each signal is registered in the type system together with the type on which
       it can be emitted: users of the type are said to <span class="emphasis"><em>connect</em></span>
       to the signal on a given type instance when they register a closure to be
       invoked upon the signal emission. Users can also emit the signal by themselves
       or stop the emission of the signal from within one of the closures connected
       to the signal.
     </p>
 <p>
       When a signal is emitted on a given type instance, all the closures
       connected to this signal on this type instance will be invoked. All the closures
       connected to such a signal represent callbacks whose signature looks like:
 </p>
 <pre class="programlisting">
 return_type function_callback (gpointer instance, ... , gpointer user_data);
 </pre>
 <p>
     </p>
 <div class="sect2" title="Signal registration">
 <div class="titlepage"><div><div><h3 class="title">
 <a name="signal-registration"></a>Signal registration</h3></div></div></div>
 <p>
 		To register a new signal on an existing type, we can use any of <code class="function"><a class="link" href="gobject-Signals.html#g-signal-newv" title="g_signal_newv ()">g_signal_newv</a></code>,
 		<code class="function"><a class="link" href="gobject-Signals.html#g-signal-new-valist" title="g_signal_new_valist ()">g_signal_new_valist</a></code> or <code class="function"><a class="link" href="gobject-Signals.html#g-signal-new" title="g_signal_new ()">g_signal_new</a></code> functions:
 </p>
 <pre class="programlisting">
 guint g_signal_newv (const gchar        *signal_name,
                      GType               itype,
                      GSignalFlags        signal_flags,
                      GClosure           *class_closure,
                      GSignalAccumulator  accumulator,
                      gpointer            accu_data,
                      GSignalCMarshaller  c_marshaller,
                      GType               return_type,
                      guint               n_params,
                      GType              *param_types);
 </pre>
 <p>
 		The number of parameters to these functions is a bit intimidating but they are relatively
 		simple:
 		</p>
 <div class="itemizedlist"><ul class="itemizedlist" type="disc">
 <li class="listitem"><p>
 			  signal_name: is a string which can be used to uniquely identify a given signal.
 			</p></li>
 <li class="listitem"><p>
 			  itype: is the instance type on which this signal can be emitted.
 			</p></li>
 <li class="listitem"><p>
 			  signal_flags: partly defines the order in which closures which were connected to the
 			  signal are invoked.
 			</p></li>
 <li class="listitem"><p>
 			  class_closure: this is the default closure for the signal: if it is not NULL upon
 			  the signal emission, it will be invoked upon this emission of the signal. The
 			  moment where this closure is invoked compared to other closures connected to that
 			  signal depends partly on the signal_flags.
 			</p></li>
 <li class="listitem"><p>
 			  accumulator: this is a function pointer which is invoked after each closure
 			  has been invoked. If it returns FALSE, signal emission is stopped. If it returns
 			  TRUE, signal emission proceeds normally. It is also used to compute the return
 			  value of the signal based on the return value of all the invoked closures.
 			</p></li>
 <li class="listitem"><p>
 			  accumulator_data: this pointer will be passed down to each invocation of the
 			  accumulator during emission.
 			</p></li>
 <li class="listitem"><p>
 			  c_marshaller: this is the default C marshaller for any closure which is connected to
 			this signal.
 			</p></li>
 <li class="listitem"><p>
 			  return_type: this is the type of the return value of the signal.
 			</p></li>
 <li class="listitem"><p>
 			  n_params: this is the number of parameters this signal takes.
 			</p></li>
 <li class="listitem"><p>
 			  param_types: this is an array of GTypes which indicate the type of each parameter
 			  of the signal. The length of this array is indicated by n_params.
 			</p></li>
 </ul></div>
 <p>
       </p>
 <p>
 		As you can see from the above definition, a signal is basically a description
 		of the closures which can be connected to this signal and a description of the
 		order in which the closures connected to this signal will be invoked.
 	  </p>
 </div>
 <div class="sect2" title="Signal connection">
 <div class="titlepage"><div><div><h3 class="title">
 <a name="signal-connection"></a>Signal connection</h3></div></div></div>
 <p>
 		If you want to connect to a signal with a closure, you have three possibilities:
 		</p>
 <div class="itemizedlist"><ul class="itemizedlist" type="disc">
 <li class="listitem"><p>
 		  You can register a class closure at signal registration: this is a
 		  system-wide operation. i.e.: the class_closure will be invoked during each emission
 		  of a given signal on all the instances of the type which supports that signal.
 			</p></li>
 <li class="listitem"><p>
 		  You can use <code class="function"><a class="link" href="gobject-Signals.html#g-signal-override-class-closure" title="g_signal_override_class_closure ()">g_signal_override_class_closure</a></code> which
 		  overrides the class_closure of a given type. It is possible to call this function
 		  only on a derived type of the type on which the signal was registered.
 		  This function is of use only to language bindings.
 			</p></li>
 <li class="listitem"><p>
 		  You can register a closure with the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-connect" title="g_signal_connect()">g_signal_connect</a></code>
 		  family of functions. This is an instance-specific operation: the closure
 		  will be invoked only during emission of a given signal on a given instance.
 			</p></li>
 </ul></div>
 <p>
 		It is also possible to connect a different kind of callback on a given signal:
 		emission hooks are invoked whenever a given signal is emitted whatever the instance on
 		which it is emitted. Emission hooks are used for example to get all mouse_clicked
 		emissions in an application to be able to emit the small mouse click sound.
 		Emission hooks are connected with <code class="function"><a class="link" href="gobject-Signals.html#g-signal-add-emission-hook" title="g_signal_add_emission_hook ()">g_signal_add_emission_hook</a></code>
 		and removed with <code class="function"><a class="link" href="gobject-Signals.html#g-signal-remove-emission-hook" title="g_signal_remove_emission_hook ()">g_signal_remove_emission_hook</a></code>.
 	  </p>
 </div>
 <div class="sect2" title="Signal emission">
 <div class="titlepage"><div><div><h3 class="title">
 <a name="signal-emission"></a>Signal emission</h3></div></div></div>
 <p>
 		Signal emission is done through the use of the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-emit" title="g_signal_emit ()">g_signal_emit</a></code> family
 		of functions.
 </p>
 <pre class="programlisting">
 void g_signal_emitv (const GValue *instance_and_params,
                      guint         signal_id,
                      GQuark        detail,
                      GValue       *return_value);
 </pre>
 <p>
 		</p>
 <div class="itemizedlist"><ul class="itemizedlist" type="disc">
 <li class="listitem"><p>
 			The instance_and_params array of GValues contains the list of input
 			parameters to the signal. The first element of the array is the
 			instance pointer on which to invoke the signal. The following elements of
 			the array contain the list of parameters to the signal.
 			</p></li>
 <li class="listitem"><p>
 			signal_id identifies the signal to invoke.
 			</p></li>
 <li class="listitem"><p>
 			detail identifies the specific detail of the signal to invoke. A detail is a kind of
 			magic token/argument which is passed around during signal emission and which is used
 			by closures connected to the signal to filter out unwanted signal emissions. In most
 			cases, you can safely set this value to zero. See <a class="xref" href="signal.html#signal-detail" title="The detail argument">the section called “The <span class="emphasis"><em>detail</em></span> argument”</a> for
 			more details about this parameter.
 			</p></li>
 <li class="listitem"><p>
 			return_value holds the return value of the last closure invoked during emission if
 			no accumulator was specified. If an accumulator was specified during signal creation,
 			this accumulator is used to calculate the return_value as a function of the return
 			values of all the closures invoked during emission.
 			<sup>[<a name="id585643" href="#ftn.id585643" class="footnote">8</a>]</sup>
 			If no closure is invoked during
 			emission, the return_value is nonetheless initialized to zero/null.
 			</p></li>
 </ul></div>
 <p>
 		</p>
 <p>
 		Internally, the GValue array is passed to the emission function proper,
 		<code class="function">signal_emit_unlocked_R</code> (implemented in <code class="filename">gsignal.c</code>).
 		Signal emission can be decomposed in 5 steps:
 		</p>
 <div class="itemizedlist"><ul class="itemizedlist" type="disc">
 <li class="listitem"><p>
 			<span class="emphasis"><em>RUN_FIRST</em></span>: if the G_SIGNAL_RUN_FIRST flag was used
 			during signal registration and if there exist a class_closure for this signal,
 			the class_closure is invoked. Jump to <span class="emphasis"><em>EMISSION_HOOK</em></span> state.
 			</p></li>
 <li class="listitem"><p>
 			<span class="emphasis"><em>EMISSION_HOOK</em></span>: if any emission hook was added to
 			the signal, they are invoked from first to last added. Accumulate return values
 			and jump to <span class="emphasis"><em>HANDLER_RUN_FIRST</em></span> state.
 			</p></li>
 <li class="listitem"><p>
 			<span class="emphasis"><em>HANDLER_RUN_FIRST</em></span>: if any closure were connected
 			with the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-connect" title="g_signal_connect()">g_signal_connect</a></code> family of
 			functions, and if they are not blocked (with the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-handler-block" title="g_signal_handler_block ()">g_signal_handler_block</a></code>
 			family of functions) they are run here, from first to last connected.
 			Jump to <span class="emphasis"><em>RUN_LAST</em></span> state.
 			</p></li>
 <li class="listitem"><p>
 			<span class="emphasis"><em>RUN_LAST</em></span>: if the G_SIGNAL_RUN_LAST
 			flag was set during registration and if a class_closure
 			was set, it is invoked here. Jump to
 			<span class="emphasis"><em>HANDLER_RUN_LAST</em></span> state.
 			</p></li>
 <li class="listitem"><p>
 			<span class="emphasis"><em>HANDLER_RUN_LAST</em></span>: if any closure were connected
 			with the <code class="function">g_signal_connect_after</code> family of
 			functions, if they were not invoked during HANDLER_RUN_FIRST and if they
 			are not blocked, they are run here, from first to last connected.
 			Jump to  <span class="emphasis"><em>RUN_CLEANUP</em></span> state.
 			</p></li>
 <li class="listitem"><p>
 			<span class="emphasis"><em>RUN_CLEANUP</em></span>: if the G_SIGNAL_RUN_CLEANUP flag
 			was set during registration and if a class_closure was set,
 			it is invoked here. Signal emission is completed here.
 			</p></li>
 </ul></div>
 <p>
 	  </p>
 <p>
 		If, at any point during emission (except in RUN_CLEANUP state), one of the
 		closures or emission hook stops the signal emission with
 		<code class="function">g_signal_stop</code>, emission jumps to CLEANUP state.
 	  </p>
 <p>
 		If, at any point during emission, one of the closures or emission hook
 		emits the same signal on the same instance, emission is restarted from
 		the RUN_FIRST state.
 	  </p>
 <p>
 		The accumulator function is invoked in all states, after invocation
 		of each closure (except in EMISSION_HOOK and CLEANUP). It accumulates
 		the closure return value into the signal return value and returns TRUE or
 		FALSE. If, at any point, it does not return TRUE, emission jumps to CLEANUP state.
 	  </p>
 <p>
 		If no accumulator function was provided, the value returned by the last handler
 		run will be returned by <code class="function"><a class="link" href="gobject-Signals.html#g-signal-emit" title="g_signal_emit ()">g_signal_emit</a></code>.
 	  </p>
 </div>
 <div class="sect2" title="The detail argument">
 <div class="titlepage"><div><div><h3 class="title">
 <a name="signal-detail"></a>The <span class="emphasis"><em>detail</em></span> argument</h3></div></div></div>
 <p>All the functions related to signal emission or signal connection have a parameter
 		named the <span class="emphasis"><em>detail</em></span>. Sometimes, this parameter is hidden by the API
 		but it is always there, under one form or another.
 	  </p>
 <p>
 	    Of the three main connection functions,
 		only one has an explicit detail parameter as a <span class="type"><a href="./../glib/glib/glib-Quarks.html#GQuark">GQuark</a></span>
 		<sup>[<a name="id585828" href="#ftn.id585828" class="footnote">9</a>]</sup>:
 </p>
 <pre class="programlisting">
 gulong     g_signal_connect_closure_by_id          (gpointer          instance,
                            guint          signal_id,
                            GQuark          detail,
                            GClosure         *closure,
                            gboolean          after);
 </pre>
 <p>
         The two other functions hide the detail parameter in the signal name identification:
 </p>
 <pre class="programlisting">
 gulong     g_signal_connect_closure          (gpointer          instance,
                            const gchar       *detailed_signal,
                            GClosure         *closure,
                            gboolean          after);
 gulong     g_signal_connect_data              (gpointer          instance,
                            const gchar     *detailed_signal,
                            GCallback      c_handler,
                            gpointer          data,
                            GClosureNotify      destroy_data,
                            GConnectFlags      connect_flags);
 </pre>
 <p>
 		Their detailed_signal parameter is a string which identifies the name of the signal
 		to connect to. However, the format of this string is structured to look like
 		<span class="emphasis"><em>signal_name::detail_name</em></span>. Connecting to the signal
 		named <span class="emphasis"><em>notify::cursor_position</em></span> will actually connect to the signal
 		named <span class="emphasis"><em>notify</em></span> with the <span class="emphasis"><em>cursor_position</em></span> name.
 		Internally, the detail string is transformed to a GQuark if it is present.
 	  </p>
 <p>
 		Of the four main signal emission functions, three have an explicit detail parameter as a
 		<span class="type"><a href="./../glib/glib/glib-Quarks.html#GQuark">GQuark</a></span> again:
 </p>
 <pre class="programlisting">
 void                  g_signal_emitv        (const GValue       *instance_and_params,
                          guint               signal_id,
                          GQuark              detail,
                          GValue             *return_value);
 void                  g_signal_emit_valist  (gpointer            instance,
                          guint               signal_id,
                          GQuark              detail,
                          va_list             var_args);
 void                  g_signal_emit         (gpointer            instance,
                          guint               signal_id,
                          GQuark              detail,
                          ...);
 </pre>
 <p>
         The fourth function hides it in its signal name parameter:
 </p>
 <pre class="programlisting">
 void                  g_signal_emit_by_name (gpointer            instance,
                          const gchar        *detailed_signal,
                          ...);
 </pre>
 <p>
         The format of the detailed_signal parameter is exactly the same as the format used by
         the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-connect" title="g_signal_connect()">g_signal_connect</a></code> functions: <span class="emphasis"><em>signal_name::detail_name</em></span>.
 	  </p>
 <p>
         If a detail is provided by the user to the emission function, it is used during emission to match
         against the closures which also provide a detail.
         If the closures' detail does not match the detail provided by the user, they will not be invoked
         (even though they are connected to a signal which is being emitted).
 	  </p>
 <p>
 		This completely optional filtering mechanism is mainly used as an optimization for signals
 		which are often emitted for many different reasons: the clients can filter out which events they are
 		interested in before the closure's marshalling code runs. For example, this is used extensively
 		by the <span class="emphasis"><em>notify</em></span> signal of GObject: whenever a property is modified on a GObject,
 		instead of just emitting the <span class="emphasis"><em>notify</em></span> signal, GObject associates as a detail to this
 		signal emission the name of the property modified. This allows clients who wish to be notified of changes
 		to only one property to filter most events before receiving them.
 	  </p>
 <p>
 		As a simple rule, users can and should set the detail parameter to zero: this will disable completely
         this optional filtering.
 	  </p>
 </div>
 <div class="footnotes">
 <br><hr width="100" align="left">
 <div class="footnote"><p><sup>[<a name="ftn.id585643" href="#id585643" class="para">8</a>] </sup>
 			  James (again!!) gives a few non-trivial examples of accumulators:
 			  <span class="quote">“<span class="quote">
 				For instance, you may have an accumulator that ignores NULL returns from
 				closures, and only accumulates the non-NULL ones. Another accumulator may try
 				to return the list of values returned by the closures.
 			  </span>”</span>
 			</p></div>
 <div class="footnote"><p><sup>[<a name="ftn.id585828" href="#id585828" class="para">9</a>] </sup>A GQuark is an integer which uniquely represents a string. It is possible to transform
 		   back and forth between the integer and string representations with the functions
 		   <code class="function"><a href="./../glib/glib/glib-Quarks.html#g-quark-from-string">g_quark_from_string</a></code> and <code class="function"><a href="./../glib/glib/glib-Quarks.html#g-quark-to-string">g_quark_to_string</a></code>.
 		  </p></div>
 </div>
 </div>
 <div class="footer">
 <hr>
           Generated by GTK-Doc V1.14</div>
 </body>
 </html>
	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
	<html>
	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
	<title>Signals</title>
	<meta name="generator" content="DocBook XSL Stylesheets V1.75.2">
	<link rel="home" href="index.html" title="GObject Reference Manual">
	<link rel="up" href="chapter-signal.html" title="The GObject messaging system">
	<link rel="prev" href="chapter-signal.html" title="The GObject messaging system">
	<link rel="next" href="rn01.html" title="API Reference">
	<meta name="generator" content="GTK-Doc V1.14 (XML mode)">
	<link rel="stylesheet" href="style.css" type="text/css">
	</head>
	<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
	<table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="2"><tr valign="middle">
	<td><a accesskey="p" href="chapter-signal.html"><img src="left.png" width="24" height="24" border="0" alt="Prev"></a></td>
	<td><a accesskey="u" href="chapter-signal.html"><img src="up.png" width="24" height="24" border="0" alt="Up"></a></td>
	<td><a accesskey="h" href="index.html"><img src="home.png" width="24" height="24" border="0" alt="Home"></a></td>
	<th width="100%" align="center">GObject Reference Manual</th>
	<td><a accesskey="n" href="rn01.html"><img src="right.png" width="24" height="24" border="0" alt="Next"></a></td>
	</tr></table>
	<div class="sect1" title="Signals">
	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
	<a name="signal"></a>Signals</h2></div></div></div>
	<p>
	GObject's signals have nothing to do with standard UNIX signals: they connect
	arbitrary application-specific events with any number of listeners.
	For example, in GTK+, every user event (keystroke or mouse move) is received
	from the X server and generates a GTK+ event under the form of a signal emission
	on a given object instance.
	</p>
	<p>
	Each signal is registered in the type system together with the type on which
	it can be emitted: users of the type are said to <span class="emphasis"><em>connect</em></span>
	to the signal on a given type instance when they register a closure to be
	invoked upon the signal emission. Users can also emit the signal by themselves
	or stop the emission of the signal from within one of the closures connected
	to the signal.
	</p>
	<p>
	When a signal is emitted on a given type instance, all the closures
	connected to this signal on this type instance will be invoked. All the closures
	connected to such a signal represent callbacks whose signature looks like:
	</p>
	<pre class="programlisting">
	return_type function_callback (gpointer instance, ... , gpointer user_data);
	</pre>
	<p>
	</p>
	<div class="sect2" title="Signal registration">
	<div class="titlepage"><div><div><h3 class="title">
	<a name="signal-registration"></a>Signal registration</h3></div></div></div>
	<p>
	To register a new signal on an existing type, we can use any of <code class="function"><a class="link" href="gobject-Signals.html#g-signal-newv" title="g_signal_newv ()">g_signal_newv</a></code>,
	<code class="function"><a class="link" href="gobject-Signals.html#g-signal-new-valist" title="g_signal_new_valist ()">g_signal_new_valist</a></code> or <code class="function"><a class="link" href="gobject-Signals.html#g-signal-new" title="g_signal_new ()">g_signal_new</a></code> functions:
	</p>
	<pre class="programlisting">
	guint g_signal_newv (const gchar *signal_name,
	GType itype,
	GSignalFlags signal_flags,
	GClosure *class_closure,
	GSignalAccumulator accumulator,
	gpointer accu_data,
	GSignalCMarshaller c_marshaller,
	GType return_type,
	guint n_params,
	GType *param_types);
	</pre>
	<p>
	The number of parameters to these functions is a bit intimidating but they are relatively
	simple:
	</p>
	<div class="itemizedlist"><ul class="itemizedlist" type="disc">
	<li class="listitem"><p>
	signal_name: is a string which can be used to uniquely identify a given signal.
	</p></li>
	<li class="listitem"><p>
	itype: is the instance type on which this signal can be emitted.
	</p></li>
	<li class="listitem"><p>
	signal_flags: partly defines the order in which closures which were connected to the
	signal are invoked.
	</p></li>
	<li class="listitem"><p>
	class_closure: this is the default closure for the signal: if it is not NULL upon
	the signal emission, it will be invoked upon this emission of the signal. The
	moment where this closure is invoked compared to other closures connected to that
	signal depends partly on the signal_flags.
	</p></li>
	<li class="listitem"><p>
	accumulator: this is a function pointer which is invoked after each closure
	has been invoked. If it returns FALSE, signal emission is stopped. If it returns
	TRUE, signal emission proceeds normally. It is also used to compute the return
	value of the signal based on the return value of all the invoked closures.
	</p></li>
	<li class="listitem"><p>
	accumulator_data: this pointer will be passed down to each invocation of the
	accumulator during emission.
	</p></li>
	<li class="listitem"><p>
	c_marshaller: this is the default C marshaller for any closure which is connected to
	this signal.
	</p></li>
	<li class="listitem"><p>
	return_type: this is the type of the return value of the signal.
	</p></li>
	<li class="listitem"><p>
	n_params: this is the number of parameters this signal takes.
	</p></li>
	<li class="listitem"><p>
	param_types: this is an array of GTypes which indicate the type of each parameter
	of the signal. The length of this array is indicated by n_params.
	</p></li>
	</ul></div>
	<p>
	</p>
	<p>
	As you can see from the above definition, a signal is basically a description
	of the closures which can be connected to this signal and a description of the
	order in which the closures connected to this signal will be invoked.
	</p>
	</div>
	<div class="sect2" title="Signal connection">
	<div class="titlepage"><div><div><h3 class="title">
	<a name="signal-connection"></a>Signal connection</h3></div></div></div>
	<p>
	If you want to connect to a signal with a closure, you have three possibilities:
	</p>
	<div class="itemizedlist"><ul class="itemizedlist" type="disc">
	<li class="listitem"><p>
	You can register a class closure at signal registration: this is a
	system-wide operation. i.e.: the class_closure will be invoked during each emission
	of a given signal on all the instances of the type which supports that signal.
	</p></li>
	<li class="listitem"><p>
	You can use <code class="function"><a class="link" href="gobject-Signals.html#g-signal-override-class-closure" title="g_signal_override_class_closure ()">g_signal_override_class_closure</a></code> which
	overrides the class_closure of a given type. It is possible to call this function
	only on a derived type of the type on which the signal was registered.
	This function is of use only to language bindings.
	</p></li>
	<li class="listitem"><p>
	You can register a closure with the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-connect" title="g_signal_connect()">g_signal_connect</a></code>
	family of functions. This is an instance-specific operation: the closure
	will be invoked only during emission of a given signal on a given instance.
	</p></li>
	</ul></div>
	<p>
	It is also possible to connect a different kind of callback on a given signal:
	emission hooks are invoked whenever a given signal is emitted whatever the instance on
	which it is emitted. Emission hooks are used for example to get all mouse_clicked
	emissions in an application to be able to emit the small mouse click sound.
	Emission hooks are connected with <code class="function"><a class="link" href="gobject-Signals.html#g-signal-add-emission-hook" title="g_signal_add_emission_hook ()">g_signal_add_emission_hook</a></code>
	and removed with <code class="function"><a class="link" href="gobject-Signals.html#g-signal-remove-emission-hook" title="g_signal_remove_emission_hook ()">g_signal_remove_emission_hook</a></code>.
	</p>
	</div>
	<div class="sect2" title="Signal emission">
	<div class="titlepage"><div><div><h3 class="title">
	<a name="signal-emission"></a>Signal emission</h3></div></div></div>
	<p>
	Signal emission is done through the use of the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-emit" title="g_signal_emit ()">g_signal_emit</a></code> family
	of functions.
	</p>
	<pre class="programlisting">
	void g_signal_emitv (const GValue *instance_and_params,
	guint signal_id,
	GQuark detail,
	GValue *return_value);
	</pre>
	<p>
	</p>
	<div class="itemizedlist"><ul class="itemizedlist" type="disc">
	<li class="listitem"><p>
	The instance_and_params array of GValues contains the list of input
	parameters to the signal. The first element of the array is the
	instance pointer on which to invoke the signal. The following elements of
	the array contain the list of parameters to the signal.
	</p></li>
	<li class="listitem"><p>
	signal_id identifies the signal to invoke.
	</p></li>
	<li class="listitem"><p>
	detail identifies the specific detail of the signal to invoke. A detail is a kind of
	magic token/argument which is passed around during signal emission and which is used
	by closures connected to the signal to filter out unwanted signal emissions. In most
	cases, you can safely set this value to zero. See <a class="xref" href="signal.html#signal-detail" title="The detail argument">the section called “The <span class="emphasis"><em>detail</em></span> argument”</a> for
	more details about this parameter.
	</p></li>
	<li class="listitem"><p>
	return_value holds the return value of the last closure invoked during emission if
	no accumulator was specified. If an accumulator was specified during signal creation,
	this accumulator is used to calculate the return_value as a function of the return
	values of all the closures invoked during emission.
	<sup>[<a name="id585643" href="#ftn.id585643" class="footnote">8</a>]</sup>
	If no closure is invoked during
	emission, the return_value is nonetheless initialized to zero/null.
	</p></li>
	</ul></div>
	<p>
	</p>
	<p>
	Internally, the GValue array is passed to the emission function proper,
	<code class="function">signal_emit_unlocked_R</code> (implemented in <code class="filename">gsignal.c</code>).
	Signal emission can be decomposed in 5 steps:
	</p>
	<div class="itemizedlist"><ul class="itemizedlist" type="disc">
	<li class="listitem"><p>
	<span class="emphasis"><em>RUN_FIRST</em></span>: if the G_SIGNAL_RUN_FIRST flag was used
	during signal registration and if there exist a class_closure for this signal,
	the class_closure is invoked. Jump to <span class="emphasis"><em>EMISSION_HOOK</em></span> state.
	</p></li>
	<li class="listitem"><p>
	<span class="emphasis"><em>EMISSION_HOOK</em></span>: if any emission hook was added to
	the signal, they are invoked from first to last added. Accumulate return values
	and jump to <span class="emphasis"><em>HANDLER_RUN_FIRST</em></span> state.
	</p></li>
	<li class="listitem"><p>
	<span class="emphasis"><em>HANDLER_RUN_FIRST</em></span>: if any closure were connected
	with the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-connect" title="g_signal_connect()">g_signal_connect</a></code> family of
	functions, and if they are not blocked (with the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-handler-block" title="g_signal_handler_block ()">g_signal_handler_block</a></code>
	family of functions) they are run here, from first to last connected.
	Jump to <span class="emphasis"><em>RUN_LAST</em></span> state.
	</p></li>
	<li class="listitem"><p>
	<span class="emphasis"><em>RUN_LAST</em></span>: if the G_SIGNAL_RUN_LAST
	flag was set during registration and if a class_closure
	was set, it is invoked here. Jump to
	<span class="emphasis"><em>HANDLER_RUN_LAST</em></span> state.
	</p></li>
	<li class="listitem"><p>
	<span class="emphasis"><em>HANDLER_RUN_LAST</em></span>: if any closure were connected
	with the <code class="function">g_signal_connect_after</code> family of
	functions, if they were not invoked during HANDLER_RUN_FIRST and if they
	are not blocked, they are run here, from first to last connected.
	Jump to <span class="emphasis"><em>RUN_CLEANUP</em></span> state.
	</p></li>
	<li class="listitem"><p>
	<span class="emphasis"><em>RUN_CLEANUP</em></span>: if the G_SIGNAL_RUN_CLEANUP flag
	was set during registration and if a class_closure was set,
	it is invoked here. Signal emission is completed here.
	</p></li>
	</ul></div>
	<p>
	</p>
	<p>
	If, at any point during emission (except in RUN_CLEANUP state), one of the
	closures or emission hook stops the signal emission with
	<code class="function">g_signal_stop</code>, emission jumps to CLEANUP state.
	</p>
	<p>
	If, at any point during emission, one of the closures or emission hook
	emits the same signal on the same instance, emission is restarted from
	the RUN_FIRST state.
	</p>
	<p>
	The accumulator function is invoked in all states, after invocation
	of each closure (except in EMISSION_HOOK and CLEANUP). It accumulates
	the closure return value into the signal return value and returns TRUE or
	FALSE. If, at any point, it does not return TRUE, emission jumps to CLEANUP state.
	</p>
	<p>
	If no accumulator function was provided, the value returned by the last handler
	run will be returned by <code class="function"><a class="link" href="gobject-Signals.html#g-signal-emit" title="g_signal_emit ()">g_signal_emit</a></code>.
	</p>
	</div>
	<div class="sect2" title="The detail argument">
	<div class="titlepage"><div><div><h3 class="title">
	<a name="signal-detail"></a>The <span class="emphasis"><em>detail</em></span> argument</h3></div></div></div>
	<p>All the functions related to signal emission or signal connection have a parameter
	named the <span class="emphasis"><em>detail</em></span>. Sometimes, this parameter is hidden by the API
	but it is always there, under one form or another.
	</p>
	<p>
	Of the three main connection functions,
	only one has an explicit detail parameter as a <span class="type"><a href="./../glib/glib/glib-Quarks.html#GQuark">GQuark</a></span>
	<sup>[<a name="id585828" href="#ftn.id585828" class="footnote">9</a>]</sup>:
	</p>
	<pre class="programlisting">
	gulong g_signal_connect_closure_by_id (gpointer instance,
	guint signal_id,
	GQuark detail,
	GClosure *closure,
	gboolean after);
	</pre>
	<p>
	The two other functions hide the detail parameter in the signal name identification:
	</p>
	<pre class="programlisting">
	gulong g_signal_connect_closure (gpointer instance,
	const gchar *detailed_signal,
	GClosure *closure,
	gboolean after);
	gulong g_signal_connect_data (gpointer instance,
	const gchar *detailed_signal,
	GCallback c_handler,
	gpointer data,
	GClosureNotify destroy_data,
	GConnectFlags connect_flags);
	</pre>
	<p>
	Their detailed_signal parameter is a string which identifies the name of the signal
	to connect to. However, the format of this string is structured to look like
	<span class="emphasis"><em>signal_name::detail_name</em></span>. Connecting to the signal
	named <span class="emphasis"><em>notify::cursor_position</em></span> will actually connect to the signal
	named <span class="emphasis"><em>notify</em></span> with the <span class="emphasis"><em>cursor_position</em></span> name.
	Internally, the detail string is transformed to a GQuark if it is present.
	</p>
	<p>
	Of the four main signal emission functions, three have an explicit detail parameter as a
	<span class="type"><a href="./../glib/glib/glib-Quarks.html#GQuark">GQuark</a></span> again:
	</p>
	<pre class="programlisting">
	void g_signal_emitv (const GValue *instance_and_params,
	guint signal_id,
	GQuark detail,
	GValue *return_value);
	void g_signal_emit_valist (gpointer instance,
	guint signal_id,
	GQuark detail,
	va_list var_args);
	void g_signal_emit (gpointer instance,
	guint signal_id,
	GQuark detail,
	...);
	</pre>
	<p>
	The fourth function hides it in its signal name parameter:
	</p>
	<pre class="programlisting">
	void g_signal_emit_by_name (gpointer instance,
	const gchar *detailed_signal,
	...);
	</pre>
	<p>
	The format of the detailed_signal parameter is exactly the same as the format used by
	the <code class="function"><a class="link" href="gobject-Signals.html#g-signal-connect" title="g_signal_connect()">g_signal_connect</a></code> functions: <span class="emphasis"><em>signal_name::detail_name</em></span>.
	</p>
	<p>
	If a detail is provided by the user to the emission function, it is used during emission to match
	against the closures which also provide a detail.
	If the closures' detail does not match the detail provided by the user, they will not be invoked
	(even though they are connected to a signal which is being emitted).
	</p>
	<p>
	This completely optional filtering mechanism is mainly used as an optimization for signals
	which are often emitted for many different reasons: the clients can filter out which events they are
	interested in before the closure's marshalling code runs. For example, this is used extensively
	by the <span class="emphasis"><em>notify</em></span> signal of GObject: whenever a property is modified on a GObject,
	instead of just emitting the <span class="emphasis"><em>notify</em></span> signal, GObject associates as a detail to this
	signal emission the name of the property modified. This allows clients who wish to be notified of changes
	to only one property to filter most events before receiving them.
	</p>
	<p>
	As a simple rule, users can and should set the detail parameter to zero: this will disable completely
	this optional filtering.
	</p>
	</div>
	<div class="footnotes">
	<br><hr width="100" align="left">
	<div class="footnote"><p><sup>[<a name="ftn.id585643" href="#id585643" class="para">8</a>] </sup>
	James (again!!) gives a few non-trivial examples of accumulators:
	<span class="quote">“<span class="quote">
	For instance, you may have an accumulator that ignores NULL returns from
	closures, and only accumulates the non-NULL ones. Another accumulator may try
	to return the list of values returned by the closures.
	</span>”</span>
	</p></div>
	<div class="footnote"><p><sup>[<a name="ftn.id585828" href="#id585828" class="para">9</a>] </sup>A GQuark is an integer which uniquely represents a string. It is possible to transform
	back and forth between the integer and string representations with the functions
	<code class="function"><a href="./../glib/glib/glib-Quarks.html#g-quark-from-string">g_quark_from_string</a></code> and <code class="function"><a href="./../glib/glib/glib-Quarks.html#g-quark-to-string">g_quark_to_string</a></code>.
	</p></div>
	</div>
	</div>
	<div class="footer">
	<hr>
	Generated by GTK-Doc V1.14</div>
	</body>
	</html>