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 <div class="refentry">
 <a name="GstBus"></a><div class="titlepage"></div>
 <div class="refnamediv"><table width="100%"><tr>
 <td valign="top">
 <h2><span class="refentrytitle"><a name="GstBus.top_of_page"></a>GstBus</span></h2>
 <p>GstBus — Asynchronous message bus subsystem</p>
 </td>
 <td class="gallery_image" valign="top" align="right"></td>
 </tr></table></div>
 <div class="refsect1">
 <a name="GstBus.functions"></a><h2>Functions</h2>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="functions_return">
 <col class="functions_name">
 </colgroup>
 <tbody>
 <tr>
 <td class="function_type">
 <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 </td>
 <td class="function_name">
 <span class="c_punctuation">(</span><a class="link" href="GstBus.html#GstBusFunc" title="GstBusFunc ()">*GstBusFunc</a><span class="c_punctuation">)</span> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a class="link" href="GstBus.html#GstBusSyncReply" title="enum GstBusSyncReply"><span class="returnvalue">GstBusSyncReply</span></a>
 </td>
 <td class="function_name">
 <span class="c_punctuation">(</span><a class="link" href="GstBus.html#GstBusSyncHandler" title="GstBusSyncHandler ()">*GstBusSyncHandler</a><span class="c_punctuation">)</span> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a class="link" href="GstBus.html" title="GstBus"><span class="returnvalue">GstBus</span></a> *
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-new" title="gst_bus_new ()">gst_bus_new</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-post" title="gst_bus_post ()">gst_bus_post</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-have-pending" title="gst_bus_have_pending ()">gst_bus_have_pending</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-peek" title="gst_bus_peek ()">gst_bus_peek</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-pop" title="gst_bus_pop ()">gst_bus_pop</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-pop-filtered" title="gst_bus_pop_filtered ()">gst_bus_pop_filtered</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-timed-pop" title="gst_bus_timed_pop ()">gst_bus_timed_pop</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-timed-pop-filtered" title="gst_bus_timed_pop_filtered ()">gst_bus_timed_pop_filtered</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <span class="returnvalue">void</span>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-set-flushing" title="gst_bus_set_flushing ()">gst_bus_set_flushing</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <span class="returnvalue">void</span>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-set-sync-handler" title="gst_bus_set_sync_handler ()">gst_bus_set_sync_handler</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a class="link" href="GstBus.html#GstBusSyncReply" title="enum GstBusSyncReply"><span class="returnvalue">GstBusSyncReply</span></a>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-sync-signal-handler" title="gst_bus_sync_signal_handler ()">gst_bus_sync_signal_handler</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#GSource"><span class="returnvalue">GSource</span></a> *
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-create-watch" title="gst_bus_create_watch ()">gst_bus_create_watch</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#guint"><span class="returnvalue">guint</span></a>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-add-watch-full" title="gst_bus_add_watch_full ()">gst_bus_add_watch_full</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#guint"><span class="returnvalue">guint</span></a>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-add-watch" title="gst_bus_add_watch ()">gst_bus_add_watch</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-remove-watch" title="gst_bus_remove_watch ()">gst_bus_remove_watch</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <span class="returnvalue">void</span>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-disable-sync-message-emission" title="gst_bus_disable_sync_message_emission ()">gst_bus_disable_sync_message_emission</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <span class="returnvalue">void</span>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-enable-sync-message-emission" title="gst_bus_enable_sync_message_emission ()">gst_bus_enable_sync_message_emission</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-async-signal-func" title="gst_bus_async_signal_func ()">gst_bus_async_signal_func</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <span class="returnvalue">void</span>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-add-signal-watch" title="gst_bus_add_signal_watch ()">gst_bus_add_signal_watch</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <span class="returnvalue">void</span>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-add-signal-watch-full" title="gst_bus_add_signal_watch_full ()">gst_bus_add_signal_watch_full</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <span class="returnvalue">void</span>
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-remove-signal-watch" title="gst_bus_remove_signal_watch ()">gst_bus_remove_signal_watch</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 <tr>
 <td class="function_type">
 <a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 </td>
 <td class="function_name">
 <a class="link" href="GstBus.html#gst-bus-poll" title="gst_bus_poll ()">gst_bus_poll</a> <span class="c_punctuation">()</span>
 </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect1">
 <a name="GstBus.properties"></a><h2>Properties</h2>
 <div class="informaltable"><table border="0">
 <colgroup>
 <col width="150px" class="properties_type">
 <col width="300px" class="properties_name">
 <col width="200px" class="properties_flags">
 </colgroup>
 <tbody><tr>
 <td class="property_type"><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="type">gboolean</span></a></td>
 <td class="property_name"><a class="link" href="GstBus.html#GstBus--enable-async" title="The “enable-async” property">enable-async</a></td>
 <td class="property_flags">Write / Construct Only</td>
 </tr></tbody>
 </table></div>
 </div>
 <div class="refsect1">
 <a name="GstBus.signals"></a><h2>Signals</h2>
 <div class="informaltable"><table border="0">
 <colgroup>
 <col width="150px" class="signals_return">
 <col width="300px" class="signals_name">
 <col width="200px" class="signals_flags">
 </colgroup>
 <tbody>
 <tr>
 <td class="signal_type"><span class="returnvalue">void</span></td>
 <td class="signal_name"><a class="link" href="GstBus.html#GstBus-message" title="The “message” signal">message</a></td>
 <td class="signal_flags"><a href="https://developer.gnome.org/gobject/unstable/gobject-Signals.html#G-SIGNAL-DETAILED:CAPS">Has Details</a></td>
 </tr>
 <tr>
 <td class="signal_type"><span class="returnvalue">void</span></td>
 <td class="signal_name"><a class="link" href="GstBus.html#GstBus-sync-message" title="The “sync-message” signal">sync-message</a></td>
 <td class="signal_flags"><a href="https://developer.gnome.org/gobject/unstable/gobject-Signals.html#G-SIGNAL-DETAILED:CAPS">Has Details</a></td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect1">
 <a name="GstBus.other"></a><h2>Types and Values</h2>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="name">
 <col class="description">
 </colgroup>
 <tbody>
 <tr>
 <td class="datatype_keyword">struct</td>
 <td class="function_name"><a class="link" href="GstBus.html#GstBus-struct" title="struct GstBus">GstBus</a></td>
 </tr>
 <tr>
 <td class="datatype_keyword">enum</td>
 <td class="function_name"><a class="link" href="GstBus.html#GstBusFlags" title="enum GstBusFlags">GstBusFlags</a></td>
 </tr>
 <tr>
 <td class="datatype_keyword">enum</td>
 <td class="function_name"><a class="link" href="GstBus.html#GstBusSyncReply" title="enum GstBusSyncReply">GstBusSyncReply</a></td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect1">
 <a name="GstBus.object-hierarchy"></a><h2>Object Hierarchy</h2>
 <pre class="screen">    <a href="https://developer.gnome.org/gobject/unstable/gobject-The-Base-Object-Type.html#GObject">GObject</a>
     <span class="lineart">╰──</span> <a href="https://developer.gnome.org/gobject/unstable/gobject-The-Base-Object-Type.html#GInitiallyUnowned">GInitiallyUnowned</a>
         <span class="lineart">╰──</span> <a class="link" href="GstObject.html" title="GstObject">GstObject</a>
             <span class="lineart">╰──</span> GstBus
 </pre>
 </div>
 <div class="refsect1">
 <a name="GstBus.includes"></a><h2>Includes</h2>
 <pre class="synopsis">#include &lt;gst/gst.h&gt;
 </pre>
 </div>
 <div class="refsect1">
 <a name="GstBus.description"></a><h2>Description</h2>
 <p>The <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> is an object responsible for delivering <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> packets in
 a first-in first-out way from the streaming threads (see <a class="link" href="GstTask.html" title="GstTask"><span class="type">GstTask</span></a>) to the
 application.</p>
 <p>Since the application typically only wants to deal with delivery of these
 messages from one thread, the GstBus will marshall the messages between
 different threads. This is important since the actual streaming of media
 is done in another thread than the application.</p>
 <p>The GstBus provides support for <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#GSource"><span class="type">GSource</span></a> based notifications. This makes it
 possible to handle the delivery in the glib mainloop.</p>
 <p>The <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#GSource"><span class="type">GSource</span></a> callback function <a class="link" href="GstBus.html#gst-bus-async-signal-func" title="gst_bus_async_signal_func ()"><code class="function">gst_bus_async_signal_func()</code></a> can be used to
 convert all bus messages into signal emissions.</p>
 <p>A message is posted on the bus with the <a class="link" href="GstBus.html#gst-bus-post" title="gst_bus_post ()"><code class="function">gst_bus_post()</code></a> method. With the
 <a class="link" href="GstBus.html#gst-bus-peek" title="gst_bus_peek ()"><code class="function">gst_bus_peek()</code></a> and <a class="link" href="GstBus.html#gst-bus-pop" title="gst_bus_pop ()"><code class="function">gst_bus_pop()</code></a> methods one can look at or retrieve a
 previously posted message.</p>
 <p>The bus can be polled with the <a class="link" href="GstBus.html#gst-bus-poll" title="gst_bus_poll ()"><code class="function">gst_bus_poll()</code></a> method. This methods blocks
 up to the specified timeout value until one of the specified messages types
 is posted on the bus. The application can then <a class="link" href="GstBus.html#gst-bus-pop" title="gst_bus_pop ()"><code class="function">gst_bus_pop()</code></a> the messages
 from the bus to handle them.
 Alternatively the application can register an asynchronous bus function
 using <a class="link" href="GstBus.html#gst-bus-add-watch-full" title="gst_bus_add_watch_full ()"><code class="function">gst_bus_add_watch_full()</code></a> or <a class="link" href="GstBus.html#gst-bus-add-watch" title="gst_bus_add_watch ()"><code class="function">gst_bus_add_watch()</code></a>. This function will
 install a <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#GSource"><span class="type">GSource</span></a> in the default glib main loop and will deliver messages
 a short while after they have been posted. Note that the main loop should
 be running for the asynchronous callbacks.</p>
 <p>It is also possible to get messages from the bus without any thread
 marshalling with the <a class="link" href="GstBus.html#gst-bus-set-sync-handler" title="gst_bus_set_sync_handler ()"><code class="function">gst_bus_set_sync_handler()</code></a> method. This makes it
 possible to react to a message in the same thread that posted the
 message on the bus. This should only be used if the application is able
 to deal with messages from different threads.</p>
 <p>Every <a class="link" href="GstPipeline.html" title="GstPipeline"><span class="type">GstPipeline</span></a> has one bus.</p>
 <p>Note that a <a class="link" href="GstPipeline.html" title="GstPipeline"><span class="type">GstPipeline</span></a> will set its bus into flushing state when changing
 from READY to NULL state.</p>
 </div>
 <div class="refsect1">
 <a name="GstBus.functions_details"></a><h2>Functions</h2>
 <div class="refsect2">
 <a name="GstBusFunc"></a><h3>GstBusFunc ()</h3>
 <pre class="programlisting"><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 <span class="c_punctuation">(</span>*GstBusFunc<span class="c_punctuation">)</span> (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                <em class="parameter"><code><a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> *message</code></em>,
                <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a> user_data</code></em>);</pre>
 <p>Specifies the type of function passed to <a class="link" href="GstBus.html#gst-bus-add-watch" title="gst_bus_add_watch ()"><code class="function">gst_bus_add_watch()</code></a> or
 <a class="link" href="GstBus.html#gst-bus-add-watch-full" title="gst_bus_add_watch_full ()"><code class="function">gst_bus_add_watch_full()</code></a>, which is called from the mainloop when a message
 is available on the bus.</p>
 <p>The message passed to the function will be unreffed after execution of this
 function so it should not be freed in the function.</p>
 <p>Note that this function is used as a GSourceFunc which means that returning
 <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> will remove the GSource from the mainloop.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.2.7"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>the <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> that sent the message</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>message</p></td>
 <td class="parameter_description"><p>the <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a></p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>user_data</p></td>
 <td class="parameter_description"><p>user data that has been given, when registering the handler</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.2.8"></a><h4>Returns</h4>
 <p> <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> if the event source should be removed.</p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="GstBusSyncHandler"></a><h3>GstBusSyncHandler ()</h3>
 <pre class="programlisting"><a class="link" href="GstBus.html#GstBusSyncReply" title="enum GstBusSyncReply"><span class="returnvalue">GstBusSyncReply</span></a>
 <span class="c_punctuation">(</span>*GstBusSyncHandler<span class="c_punctuation">)</span> (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                       <em class="parameter"><code><a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> *message</code></em>,
                       <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a> user_data</code></em>);</pre>
 <p>Handler will be invoked synchronously, when a new message has been injected
 into the bus. This function is mostly used internally. Only one sync handler
 can be attached to a given bus.</p>
 <p>If the handler returns GST_BUS_DROP, it should unref the message, else the
 message should not be unreffed by the sync handler.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.3.6"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>the <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> that sent the message</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>message</p></td>
 <td class="parameter_description"><p>the <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a></p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>user_data</p></td>
 <td class="parameter_description"><p>user data that has been given, when registering the handler</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.3.7"></a><h4>Returns</h4>
 <p> <a class="link" href="GstBus.html#GstBusSyncReply" title="enum GstBusSyncReply"><span class="type">GstBusSyncReply</span></a> stating what to do with the message</p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-new"></a><h3>gst_bus_new ()</h3>
 <pre class="programlisting"><a class="link" href="GstBus.html" title="GstBus"><span class="returnvalue">GstBus</span></a> *
 gst_bus_new (<em class="parameter"><code><span class="type">void</span></code></em>);</pre>
 <p>Creates a new <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> instance.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.4.5"></a><h4>Returns</h4>
 <p> a new <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> instance. </p>
 <p><span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>]</span></p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-post"></a><h3>gst_bus_post ()</h3>
 <pre class="programlisting"><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 gst_bus_post (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
               <em class="parameter"><code><a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> *message</code></em>);</pre>
 <p>Post a message on the given bus. Ownership of the message
 is taken by the bus.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.5.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to post on</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>message</p></td>
 <td class="parameter_description"><p> the <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> to post. </p></td>
 <td class="parameter_annotations"><span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>]</span></td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.5.6"></a><h4>Returns</h4>
 <p> <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> if the message could be posted, <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> if the bus is flushing.</p>
 <p>MT safe.</p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-have-pending"></a><h3>gst_bus_have_pending ()</h3>
 <pre class="programlisting"><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 gst_bus_have_pending (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>);</pre>
 <p>Check if there are pending messages on the bus that
 should be handled.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.6.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody><tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to check</p></td>
 <td class="parameter_annotations"> </td>
 </tr></tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.6.6"></a><h4>Returns</h4>
 <p> <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> if there are messages on the bus to be handled, <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a>
 otherwise.</p>
 <p>MT safe.</p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-peek"></a><h3>gst_bus_peek ()</h3>
 <pre class="programlisting"><a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 gst_bus_peek (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>);</pre>
 <p>Peek the message on the top of the bus' queue. The message will remain
 on the bus' message queue. A reference is returned, and needs to be unreffed
 by the caller.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.7.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody><tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a></p></td>
 <td class="parameter_annotations"> </td>
 </tr></tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.7.6"></a><h4>Returns</h4>
 <p> the <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> that is on the
 bus, or <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> if the bus is empty.</p>
 <p>MT safe. </p>
 <p><span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>][<acronym title="NULL may be passed as the value in, out, in-out; or as a return value."><span class="acronym">nullable</span></acronym>]</span></p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-pop"></a><h3>gst_bus_pop ()</h3>
 <pre class="programlisting"><a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 gst_bus_pop (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>);</pre>
 <p>Get a message from the bus.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.8.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody><tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to pop</p></td>
 <td class="parameter_annotations"> </td>
 </tr></tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.8.6"></a><h4>Returns</h4>
 <p> the <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> that is on the
 bus, or <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> if the bus is empty. The message is taken from
 the bus and needs to be unreffed with <a class="link" href="GstMessage.html#gst-message-unref" title="gst_message_unref ()"><code class="function">gst_message_unref()</code></a> after
 usage.</p>
 <p>MT safe. </p>
 <p><span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>][<acronym title="NULL may be passed as the value in, out, in-out; or as a return value."><span class="acronym">nullable</span></acronym>]</span></p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-pop-filtered"></a><h3>gst_bus_pop_filtered ()</h3>
 <pre class="programlisting"><a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 gst_bus_pop_filtered (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                       <em class="parameter"><code><a class="link" href="GstMessage.html#GstMessageType" title="enum GstMessageType"><span class="type">GstMessageType</span></a> types</code></em>);</pre>
 <p>Get a message matching <em class="parameter"><code>type</code></em>
  from the bus.  Will discard all messages on
 the bus that do not match <em class="parameter"><code>type</code></em>
  and that have been posted before the first
 message that does match <em class="parameter"><code>type</code></em>
 .  If there is no message matching <em class="parameter"><code>type</code></em>
  on
 the bus, all messages will be discarded. It is not possible to use message
 enums beyond <a class="link" href="GstMessage.html#GST-MESSAGE-EXTENDED:CAPS"><span class="type">GST_MESSAGE_EXTENDED</span></a> in the <em class="parameter"><code>events</code></em>
  mask.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.9.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to pop</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>types</p></td>
 <td class="parameter_description"><p>message types to take into account</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.9.6"></a><h4>Returns</h4>
 <p> the next <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> matching
 <em class="parameter"><code>type</code></em>
 that is on the bus, or <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> if the bus is empty or there
 is no message matching <em class="parameter"><code>type</code></em>
 . The message is taken from the bus
 and needs to be unreffed with <a class="link" href="GstMessage.html#gst-message-unref" title="gst_message_unref ()"><code class="function">gst_message_unref()</code></a> after usage.</p>
 <p>MT safe. </p>
 <p><span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>][<acronym title="NULL may be passed as the value in, out, in-out; or as a return value."><span class="acronym">nullable</span></acronym>]</span></p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-timed-pop"></a><h3>gst_bus_timed_pop ()</h3>
 <pre class="programlisting"><a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 gst_bus_timed_pop (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                    <em class="parameter"><code><a class="link" href="GstClock.html#GstClockTime" title="GstClockTime"><span class="type">GstClockTime</span></a> timeout</code></em>);</pre>
 <p>Get a message from the bus, waiting up to the specified timeout.</p>
 <p>If <em class="parameter"><code>timeout</code></em>
  is 0, this function behaves like <a class="link" href="GstBus.html#gst-bus-pop" title="gst_bus_pop ()"><code class="function">gst_bus_pop()</code></a>. If <em class="parameter"><code>timeout</code></em>
  is
 <a class="link" href="GstClock.html#GST-CLOCK-TIME-NONE:CAPS" title="GST_CLOCK_TIME_NONE"><span class="type">GST_CLOCK_TIME_NONE</span></a>, this function will block forever until a message was
 posted on the bus.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.10.6"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to pop</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>timeout</p></td>
 <td class="parameter_description"><p>a timeout</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.10.7"></a><h4>Returns</h4>
 <p> the <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> that is on the
 bus after the specified timeout or <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> if the bus is empty
 after the timeout expired.  The message is taken from the bus
 and needs to be unreffed with <a class="link" href="GstMessage.html#gst-message-unref" title="gst_message_unref ()"><code class="function">gst_message_unref()</code></a> after usage.</p>
 <p>MT safe. </p>
 <p><span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>][<acronym title="NULL may be passed as the value in, out, in-out; or as a return value."><span class="acronym">nullable</span></acronym>]</span></p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-timed-pop-filtered"></a><h3>gst_bus_timed_pop_filtered ()</h3>
 <pre class="programlisting"><a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 gst_bus_timed_pop_filtered (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                             <em class="parameter"><code><a class="link" href="GstClock.html#GstClockTime" title="GstClockTime"><span class="type">GstClockTime</span></a> timeout</code></em>,
                             <em class="parameter"><code><a class="link" href="GstMessage.html#GstMessageType" title="enum GstMessageType"><span class="type">GstMessageType</span></a> types</code></em>);</pre>
 <p>Get a message from the bus whose type matches the message type mask <em class="parameter"><code>types</code></em>
 ,
 waiting up to the specified timeout (and discarding any messages that do not
 match the mask provided).</p>
 <p>If <em class="parameter"><code>timeout</code></em>
  is 0, this function behaves like <a class="link" href="GstBus.html#gst-bus-pop-filtered" title="gst_bus_pop_filtered ()"><code class="function">gst_bus_pop_filtered()</code></a>. If
 <em class="parameter"><code>timeout</code></em>
  is <a class="link" href="GstClock.html#GST-CLOCK-TIME-NONE:CAPS" title="GST_CLOCK_TIME_NONE"><span class="type">GST_CLOCK_TIME_NONE</span></a>, this function will block forever until a
 matching message was posted on the bus.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.11.6"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to pop from</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>timeout</p></td>
 <td class="parameter_description"><p>a timeout in nanoseconds, or GST_CLOCK_TIME_NONE to wait forever</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>types</p></td>
 <td class="parameter_description"><p>message types to take into account, GST_MESSAGE_ANY for any type</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.11.7"></a><h4>Returns</h4>
 <p> a <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> matching the
 filter in <em class="parameter"><code>types</code></em>
 , or <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> if no matching message was found on
 the bus until the timeout expired. The message is taken from
 the bus and needs to be unreffed with <a class="link" href="GstMessage.html#gst-message-unref" title="gst_message_unref ()"><code class="function">gst_message_unref()</code></a> after
 usage.</p>
 <p>MT safe. </p>
 <p><span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>][<acronym title="NULL may be passed as the value in, out, in-out; or as a return value."><span class="acronym">nullable</span></acronym>]</span></p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-set-flushing"></a><h3>gst_bus_set_flushing ()</h3>
 <pre class="programlisting"><span class="returnvalue">void</span>
 gst_bus_set_flushing (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                       <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="type">gboolean</span></a> flushing</code></em>);</pre>
 <p>If <em class="parameter"><code>flushing</code></em>
 , flush out and unref any messages queued in the bus. Releases
 references to the message origin objects. Will flush future messages until
 <a class="link" href="GstBus.html#gst-bus-set-flushing" title="gst_bus_set_flushing ()"><code class="function">gst_bus_set_flushing()</code></a> sets <em class="parameter"><code>flushing</code></em>
  to <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a>.</p>
 <p>MT safe.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.12.6"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a></p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>flushing</p></td>
 <td class="parameter_description"><p>whether or not to flush the bus</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-set-sync-handler"></a><h3>gst_bus_set_sync_handler ()</h3>
 <pre class="programlisting"><span class="returnvalue">void</span>
 gst_bus_set_sync_handler (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                           <em class="parameter"><code><a class="link" href="GstBus.html#GstBusSyncHandler" title="GstBusSyncHandler ()"><span class="type">GstBusSyncHandler</span></a> func</code></em>,
                           <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a> user_data</code></em>,
                           <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Datasets.html#GDestroyNotify"><span class="type">GDestroyNotify</span></a> notify</code></em>);</pre>
 <p>Sets the synchronous handler on the bus. The function will be called
 every time a new message is posted on the bus. Note that the function
 will be called in the same thread context as the posting object. This
 function is usually only called by the creator of the bus. Applications
 should handle messages asynchronously using the gst_bus watch and poll
 functions.</p>
 <p>You cannot replace an existing sync_handler. You can pass <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> to this
 function, which will clear the existing handler.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.13.6"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to install the handler on</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>func</p></td>
 <td class="parameter_description"><p> The handler function to install. </p></td>
 <td class="parameter_annotations"><span class="annotation">[<acronym title="NULL is OK, both for passing and for returning."><span class="acronym">allow-none</span></acronym>]</span></td>
 </tr>
 <tr>
 <td class="parameter_name"><p>user_data</p></td>
 <td class="parameter_description"><p>User data that will be sent to the handler function.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>notify</p></td>
 <td class="parameter_description"><p>called when <em class="parameter"><code>user_data</code></em>
 becomes unused</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-sync-signal-handler"></a><h3>gst_bus_sync_signal_handler ()</h3>
 <pre class="programlisting"><a class="link" href="GstBus.html#GstBusSyncReply" title="enum GstBusSyncReply"><span class="returnvalue">GstBusSyncReply</span></a>
 gst_bus_sync_signal_handler (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                              <em class="parameter"><code><a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> *message</code></em>,
                              <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a> data</code></em>);</pre>
 <p>A helper GstBusSyncHandler that can be used to convert all synchronous
 messages into signals.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.14.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a></p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>message</p></td>
 <td class="parameter_description"><p>the <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> received</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>data</p></td>
 <td class="parameter_description"><p>user data</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.14.6"></a><h4>Returns</h4>
 <p> GST_BUS_PASS</p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-create-watch"></a><h3>gst_bus_create_watch ()</h3>
 <pre class="programlisting"><a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#GSource"><span class="returnvalue">GSource</span></a> *
 gst_bus_create_watch (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>);</pre>
 <p>Create watch for this bus. The GSource will be dispatched whenever
 a message is on the bus. After the GSource is dispatched, the
 message is popped off the bus and unreffed.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.15.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody><tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to create the watch for</p></td>
 <td class="parameter_annotations"> </td>
 </tr></tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.15.6"></a><h4>Returns</h4>
 <p> a <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#GSource"><span class="type">GSource</span></a> that can be added to a mainloop. </p>
 <p><span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>]</span></p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-add-watch-full"></a><h3>gst_bus_add_watch_full ()</h3>
 <pre class="programlisting"><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#guint"><span class="returnvalue">guint</span></a>
 gst_bus_add_watch_full (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                         <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gint"><span class="type">gint</span></a> priority</code></em>,
                         <em class="parameter"><code><a class="link" href="GstBus.html#GstBusFunc" title="GstBusFunc ()"><span class="type">GstBusFunc</span></a> func</code></em>,
                         <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a> user_data</code></em>,
                         <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Datasets.html#GDestroyNotify"><span class="type">GDestroyNotify</span></a> notify</code></em>);</pre>
 <p>Adds a bus watch to the default main context with the given <em class="parameter"><code>priority</code></em>
  (e.g.
 <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#G-PRIORITY-DEFAULT:CAPS"><code class="literal">G_PRIORITY_DEFAULT</code></a>). It is also possible to use a non-default  main
 context set up using <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#g-main-context-push-thread-default"><code class="function">g_main_context_push_thread_default()</code></a> (before
 one had to create a bus watch source and attach it to the desired main
 context 'manually').</p>
 <p>This function is used to receive asynchronous messages in the main loop.
 There can only be a single bus watch per bus, you must remove it before you
 can set a new one.</p>
 <p>When <em class="parameter"><code>func</code></em>
  is called, the message belongs to the caller; if you want to
 keep a copy of it, call <a class="link" href="GstMessage.html#gst-message-ref" title="gst_message_ref ()"><code class="function">gst_message_ref()</code></a> before leaving <em class="parameter"><code>func</code></em>
 .</p>
 <p>The watch can be removed using <a class="link" href="GstBus.html#gst-bus-remove-watch" title="gst_bus_remove_watch ()"><code class="function">gst_bus_remove_watch()</code></a> or by returning <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a>
 from <em class="parameter"><code>func</code></em>
 . If the watch was added to the default main context it is also
 possible to remove the watch using <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#g-source-remove"><code class="function">g_source_remove()</code></a>.</p>
 <p>MT safe.</p>
 <p><span class="annotation">[<acronym title="Rename the original symbol's name to SYMBOL."><span class="acronym">rename-to</span></acronym> gst_bus_add_watch]</span></p>
 <div class="refsect3">
 <a name="id-1.3.10.10.16.10"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to create the watch for.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>priority</p></td>
 <td class="parameter_description"><p>The priority of the watch.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>func</p></td>
 <td class="parameter_description"><p>A function to call when a message is received.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>user_data</p></td>
 <td class="parameter_description"><p>user data passed to <em class="parameter"><code>func</code></em>
 .</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>notify</p></td>
 <td class="parameter_description"><p>the function to call when the source is removed.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.16.11"></a><h4>Returns</h4>
 <p> The event source id or 0 if <em class="parameter"><code>bus</code></em>
 already got an event source.</p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-add-watch"></a><h3>gst_bus_add_watch ()</h3>
 <pre class="programlisting"><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#guint"><span class="returnvalue">guint</span></a>
 gst_bus_add_watch (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                    <em class="parameter"><code><a class="link" href="GstBus.html#GstBusFunc" title="GstBusFunc ()"><span class="type">GstBusFunc</span></a> func</code></em>,
                    <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a> user_data</code></em>);</pre>
 <p>Adds a bus watch to the default main context with the default priority
 (<a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#G-PRIORITY-DEFAULT:CAPS"><code class="literal">G_PRIORITY_DEFAULT</code></a>). It is also possible to use a non-default main
 context set up using <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#g-main-context-push-thread-default"><code class="function">g_main_context_push_thread_default()</code></a> (before
 one had to create a bus watch source and attach it to the desired main
 context 'manually').</p>
 <p>This function is used to receive asynchronous messages in the main loop.
 There can only be a single bus watch per bus, you must remove it before you
 can set a new one.</p>
 <p>The watch can be removed using <a class="link" href="GstBus.html#gst-bus-remove-watch" title="gst_bus_remove_watch ()"><code class="function">gst_bus_remove_watch()</code></a> or by returning <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a>
 from <em class="parameter"><code>func</code></em>
 . If the watch was added to the default main context it is also
 possible to remove the watch using <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#g-source-remove"><code class="function">g_source_remove()</code></a>.</p>
 <p><span class="annotation">[<acronym title="Exposed in C code, not necessarily available in other languages."><span class="acronym">skip</span></acronym>]</span></p>
 <div class="refsect3">
 <a name="id-1.3.10.10.17.8"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to create the watch for</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>func</p></td>
 <td class="parameter_description"><p>A function to call when a message is received.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>user_data</p></td>
 <td class="parameter_description"><p>user data passed to <em class="parameter"><code>func</code></em>
 .</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.17.9"></a><h4>Returns</h4>
 <p> The event source id or 0 if <em class="parameter"><code>bus</code></em>
 already got an event source.</p>
 <p>MT safe.</p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-remove-watch"></a><h3>gst_bus_remove_watch ()</h3>
 <pre class="programlisting"><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 gst_bus_remove_watch (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>);</pre>
 <p>Removes an installed bus watch from <em class="parameter"><code>bus</code></em>
 .</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.18.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody><tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> to remove the watch from.</p></td>
 <td class="parameter_annotations"> </td>
 </tr></tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.18.6"></a><h4>Returns</h4>
 <p> <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> on success or <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> if <em class="parameter"><code>bus</code></em>
 has no event source.</p>
 </div>
 <p class="since">Since: <a class="link" href="ix03.html#api-index-1.6">1.6</a></p>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-disable-sync-message-emission"></a><h3>gst_bus_disable_sync_message_emission ()</h3>
 <pre class="programlisting"><span class="returnvalue">void</span>
 gst_bus_disable_sync_message_emission (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>);</pre>
 <p>Instructs GStreamer to stop emitting the "sync-message" signal for this bus.
 See <a class="link" href="GstBus.html#gst-bus-enable-sync-message-emission" title="gst_bus_enable_sync_message_emission ()"><code class="function">gst_bus_enable_sync_message_emission()</code></a> for more information.</p>
 <p>In the event that multiple pieces of code have called
 <a class="link" href="GstBus.html#gst-bus-enable-sync-message-emission" title="gst_bus_enable_sync_message_emission ()"><code class="function">gst_bus_enable_sync_message_emission()</code></a>, the sync-message emissions will only
 be stopped after all calls to <a class="link" href="GstBus.html#gst-bus-enable-sync-message-emission" title="gst_bus_enable_sync_message_emission ()"><code class="function">gst_bus_enable_sync_message_emission()</code></a> were
 "cancelled" by calling this function. In this way the semantics are exactly
 the same as <a class="link" href="GstObject.html#gst-object-ref" title="gst_object_ref ()"><code class="function">gst_object_ref()</code></a> that which calls enable should also call
 disable.</p>
 <p>MT safe.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.19.7"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody><tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> on which you previously called
 <a class="link" href="GstBus.html#gst-bus-enable-sync-message-emission" title="gst_bus_enable_sync_message_emission ()"><code class="function">gst_bus_enable_sync_message_emission()</code></a></p></td>
 <td class="parameter_annotations"> </td>
 </tr></tbody>
 </table></div>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-enable-sync-message-emission"></a><h3>gst_bus_enable_sync_message_emission ()</h3>
 <pre class="programlisting"><span class="returnvalue">void</span>
 gst_bus_enable_sync_message_emission (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>);</pre>
 <p>Instructs GStreamer to emit the "sync-message" signal after running the bus's
 sync handler. This function is here so that code can ensure that they can
 synchronously receive messages without having to affect what the bin's sync
 handler is.</p>
 <p>This function may be called multiple times. To clean up, the caller is
 responsible for calling <a class="link" href="GstBus.html#gst-bus-disable-sync-message-emission" title="gst_bus_disable_sync_message_emission ()"><code class="function">gst_bus_disable_sync_message_emission()</code></a> as many times
 as this function is called.</p>
 <p>While this function looks similar to <a class="link" href="GstBus.html#gst-bus-add-signal-watch" title="gst_bus_add_signal_watch ()"><code class="function">gst_bus_add_signal_watch()</code></a>, it is not
 exactly the same -- this function enables <span class="emphasis"><em>synchronous</em></span> emission of
 signals when messages arrive; <a class="link" href="GstBus.html#gst-bus-add-signal-watch" title="gst_bus_add_signal_watch ()"><code class="function">gst_bus_add_signal_watch()</code></a> adds an idle callback
 to pop messages off the bus <span class="emphasis"><em>asynchronously</em></span>. The sync-message signal
 comes from the thread of whatever object posted the message; the "message"
 signal is marshalled to the main thread via the main loop.</p>
 <p>MT safe.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.20.8"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody><tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> on which you want to receive the "sync-message" signal</p></td>
 <td class="parameter_annotations"> </td>
 </tr></tbody>
 </table></div>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-async-signal-func"></a><h3>gst_bus_async_signal_func ()</h3>
 <pre class="programlisting"><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
 gst_bus_async_signal_func (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                            <em class="parameter"><code><a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> *message</code></em>,
                            <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a> data</code></em>);</pre>
 <p>A helper <a class="link" href="GstBus.html#GstBusFunc" title="GstBusFunc ()"><span class="type">GstBusFunc</span></a> that can be used to convert all asynchronous messages
 into signals.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.21.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a></p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>message</p></td>
 <td class="parameter_description"><p>the <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> received</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>data</p></td>
 <td class="parameter_description"><p>user data</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.21.6"></a><h4>Returns</h4>
 <p> <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a></p>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-add-signal-watch"></a><h3>gst_bus_add_signal_watch ()</h3>
 <pre class="programlisting"><span class="returnvalue">void</span>
 gst_bus_add_signal_watch (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>);</pre>
 <p>Adds a bus signal watch to the default main context with the default priority
 (<a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#G-PRIORITY-DEFAULT:CAPS"><code class="literal">G_PRIORITY_DEFAULT</code></a>). It is also possible to use a non-default
 main context set up using <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#g-main-context-push-thread-default"><code class="function">g_main_context_push_thread_default()</code></a> (before
 one had to create a bus watch source and attach it to the desired main
 context 'manually').</p>
 <p>After calling this statement, the bus will emit the "message" signal for each
 message posted on the bus.</p>
 <p>This function may be called multiple times. To clean up, the caller is
 responsible for calling <a class="link" href="GstBus.html#gst-bus-remove-signal-watch" title="gst_bus_remove_signal_watch ()"><code class="function">gst_bus_remove_signal_watch()</code></a> as many times as this
 function is called.</p>
 <p>MT safe.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.22.8"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody><tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> on which you want to receive the "message" signal</p></td>
 <td class="parameter_annotations"> </td>
 </tr></tbody>
 </table></div>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-add-signal-watch-full"></a><h3>gst_bus_add_signal_watch_full ()</h3>
 <pre class="programlisting"><span class="returnvalue">void</span>
 gst_bus_add_signal_watch_full (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
                                <em class="parameter"><code><a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gint"><span class="type">gint</span></a> priority</code></em>);</pre>
 <p>Adds a bus signal watch to the default main context with the given <em class="parameter"><code>priority</code></em>

 (e.g. <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#G-PRIORITY-DEFAULT:CAPS"><code class="literal">G_PRIORITY_DEFAULT</code></a>). It is also possible to use a non-default main
 context set up using <a href="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html#g-main-context-push-thread-default"><code class="function">g_main_context_push_thread_default()</code></a>
 (before one had to create a bus watch source and attach it to the desired
 main context 'manually').</p>
 <p>After calling this statement, the bus will emit the "message" signal for each
 message posted on the bus when the main loop is running.</p>
 <p>This function may be called multiple times. To clean up, the caller is
 responsible for calling <a class="link" href="GstBus.html#gst-bus-remove-signal-watch" title="gst_bus_remove_signal_watch ()"><code class="function">gst_bus_remove_signal_watch()</code></a> as many times as this
 function is called.</p>
 <p>There can only be a single bus watch per bus, you must remove any signal
 watch before you can set another type of watch.</p>
 <p>MT safe.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.23.9"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> on which you want to receive the "message" signal</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>priority</p></td>
 <td class="parameter_description"><p>The priority of the watch.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-remove-signal-watch"></a><h3>gst_bus_remove_signal_watch ()</h3>
 <pre class="programlisting"><span class="returnvalue">void</span>
 gst_bus_remove_signal_watch (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>);</pre>
 <p>Removes a signal watch previously added with <a class="link" href="GstBus.html#gst-bus-add-signal-watch" title="gst_bus_add_signal_watch ()"><code class="function">gst_bus_add_signal_watch()</code></a>.</p>
 <p>MT safe.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.24.6"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody><tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> you previously added a signal watch to</p></td>
 <td class="parameter_annotations"> </td>
 </tr></tbody>
 </table></div>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="gst-bus-poll"></a><h3>gst_bus_poll ()</h3>
 <pre class="programlisting"><a class="link" href="GstMessage.html" title="GstMessage"><span class="returnvalue">GstMessage</span></a> *
 gst_bus_poll (<em class="parameter"><code><a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> *bus</code></em>,
               <em class="parameter"><code><a class="link" href="GstMessage.html#GstMessageType" title="enum GstMessageType"><span class="type">GstMessageType</span></a> events</code></em>,
               <em class="parameter"><code><a class="link" href="GstClock.html#GstClockTime" title="GstClockTime"><span class="type">GstClockTime</span></a> timeout</code></em>);</pre>
 <p>Poll the bus for messages. Will block while waiting for messages to come.
 You can specify a maximum time to poll with the <em class="parameter"><code>timeout</code></em>
  parameter. If
 <em class="parameter"><code>timeout</code></em>
  is negative, this function will block indefinitely.</p>
 <p>All messages not in <em class="parameter"><code>events</code></em>
  will be popped off the bus and will be ignored.
 It is not possible to use message enums beyond <a class="link" href="GstMessage.html#GST-MESSAGE-EXTENDED:CAPS"><span class="type">GST_MESSAGE_EXTENDED</span></a> in the
 <em class="parameter"><code>events</code></em>
  mask</p>
 <p>Because poll is implemented using the "message" signal enabled by
 <a class="link" href="GstBus.html#gst-bus-add-signal-watch" title="gst_bus_add_signal_watch ()"><code class="function">gst_bus_add_signal_watch()</code></a>, calling <a class="link" href="GstBus.html#gst-bus-poll" title="gst_bus_poll ()"><code class="function">gst_bus_poll()</code></a> will cause the "message"
 signal to be emitted for every message that poll sees. Thus a "message"
 signal handler will see the same messages that this function sees -- neither
 will steal messages from the other.</p>
 <p>This function will run a main loop from the default main context when
 polling.</p>
 <p>You should never use this function, since it is pure evil. This is
 especially true for GUI applications based on Gtk+ or Qt, but also for any
 other non-trivial application that uses the GLib main loop. As this function
 runs a GLib main loop, any callback attached to the default GLib main
 context may be invoked. This could be timeouts, GUI events, I/O events etc.;
 even if <a class="link" href="GstBus.html#gst-bus-poll" title="gst_bus_poll ()"><code class="function">gst_bus_poll()</code></a> is called with a 0 timeout. Any of these callbacks
 may do things you do not expect, e.g. destroy the main application window or
 some other resource; change other application state; display a dialog and
 run another main loop until the user clicks it away. In short, using this
 function may add a lot of complexity to your code through unexpected
 re-entrancy and unexpected changes to your application's state.</p>
 <p>For 0 timeouts use <a class="link" href="GstBus.html#gst-bus-pop-filtered" title="gst_bus_pop_filtered ()"><code class="function">gst_bus_pop_filtered()</code></a> instead of this function; for
 other short timeouts use <a class="link" href="GstBus.html#gst-bus-timed-pop-filtered" title="gst_bus_timed_pop_filtered ()"><code class="function">gst_bus_timed_pop_filtered()</code></a>; everything else is
 better handled by setting up an asynchronous bus watch and doing things
 from there.</p>
 <div class="refsect3">
 <a name="id-1.3.10.10.25.10"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>a <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a></p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>events</p></td>
 <td class="parameter_description"><p>a mask of <a class="link" href="GstMessage.html#GstMessageType" title="enum GstMessageType"><span class="type">GstMessageType</span></a>, representing the set of message types to
 poll for (note special handling of extended message types below)</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>timeout</p></td>
 <td class="parameter_description"><p>the poll timeout, as a <a class="link" href="GstClock.html#GstClockTime" title="GstClockTime"><span class="type">GstClockTime</span></a>, or <a class="link" href="GstClock.html#GST-CLOCK-TIME-NONE:CAPS" title="GST_CLOCK_TIME_NONE"><span class="type">GST_CLOCK_TIME_NONE</span></a> to poll
 indefinitely.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <div class="refsect3">
 <a name="id-1.3.10.10.25.11"></a><h4>Returns</h4>
 <p> the message that was received,
 or <a href="https://developer.gnome.org/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> if the poll timed out. The message is taken from the
 bus and needs to be unreffed with <a class="link" href="GstMessage.html#gst-message-unref" title="gst_message_unref ()"><code class="function">gst_message_unref()</code></a> after
 usage. </p>
 <p><span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>][<acronym title="NULL may be passed as the value in, out, in-out; or as a return value."><span class="acronym">nullable</span></acronym>]</span></p>
 </div>
 </div>
 </div>
 <div class="refsect1">
 <a name="GstBus.other_details"></a><h2>Types and Values</h2>
 <div class="refsect2">
 <a name="GstBus-struct"></a><h3>struct GstBus</h3>
 <pre class="programlisting">struct GstBus;</pre>
 <p>The opaque <a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a> data structure.</p>
 </div>
 <hr>
 <div class="refsect2">
 <a name="GstBusFlags"></a><h3>enum GstBusFlags</h3>
 <p>The standard flags that a bus may have.</p>
 <div class="refsect3">
 <a name="id-1.3.10.11.3.4"></a><h4>Members</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="300px" class="enum_members_name">
 <col class="enum_members_description">
 <col width="200px" class="enum_members_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="enum_member_name"><p><a name="GST-BUS-FLUSHING:CAPS"></a>GST_BUS_FLUSHING</p></td>
 <td class="enum_member_description">
 <p>The bus is currently dropping all messages</p>
 </td>
 <td class="enum_member_annotations"> </td>
 </tr>
 <tr>
 <td class="enum_member_name"><p><a name="GST-BUS-FLAG-LAST:CAPS"></a>GST_BUS_FLAG_LAST</p></td>
 <td class="enum_member_description">
 <p>offset to define more flags</p>
 </td>
 <td class="enum_member_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 </div>
 <hr>
 <div class="refsect2">
 <a name="GstBusSyncReply"></a><h3>enum GstBusSyncReply</h3>
 <p>The result values for a GstBusSyncHandler.</p>
 <div class="refsect3">
 <a name="id-1.3.10.11.4.4"></a><h4>Members</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="300px" class="enum_members_name">
 <col class="enum_members_description">
 <col width="200px" class="enum_members_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="enum_member_name"><p><a name="GST-BUS-DROP:CAPS"></a>GST_BUS_DROP</p></td>
 <td class="enum_member_description">
 <p>drop the message</p>
 </td>
 <td class="enum_member_annotations"> </td>
 </tr>
 <tr>
 <td class="enum_member_name"><p><a name="GST-BUS-PASS:CAPS"></a>GST_BUS_PASS</p></td>
 <td class="enum_member_description">
 <p>pass the message to the async queue</p>
 </td>
 <td class="enum_member_annotations"> </td>
 </tr>
 <tr>
 <td class="enum_member_name"><p><a name="GST-BUS-ASYNC:CAPS"></a>GST_BUS_ASYNC</p></td>
 <td class="enum_member_description">
 <p>pass message to async queue, continue if message is handled</p>
 </td>
 <td class="enum_member_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 </div>
 </div>
 <div class="refsect1">
 <a name="GstBus.property-details"></a><h2>Property Details</h2>
 <div class="refsect2">
 <a name="GstBus--enable-async"></a><h3>The <code class="literal">“enable-async”</code> property</h3>
 <pre class="programlisting">  “enable-async”             <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gboolean"><span class="type">gboolean</span></a></pre>
 <p>Enable async message delivery for bus watches and gst_bus_pop().</p>
 <p>Flags: Write / Construct Only</p>
 <p>Default value: TRUE</p>
 </div>
 </div>
 <div class="refsect1">
 <a name="GstBus.signal-details"></a><h2>Signal Details</h2>
 <div class="refsect2">
 <a name="GstBus-message"></a><h3>The <code class="literal">“message”</code> signal</h3>
 <pre class="programlisting"><span class="returnvalue">void</span>
 user_function (<a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a>     *bus,
                <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> *message,
                <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a>    user_data)</pre>
 <p>A message has been posted on the bus. This signal is emitted from a
 GSource added to the mainloop. this signal will only be emitted when
 there is a mainloop running.</p>
 <div class="refsect3">
 <a name="id-1.3.10.13.2.5"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>the object which received the signal</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>message</p></td>
 <td class="parameter_description"><p>the message that has been posted asynchronously</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>user_data</p></td>
 <td class="parameter_description"><p>user data set when the signal handler was connected.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <p>Flags: <a href="https://developer.gnome.org/gobject/unstable/gobject-Signals.html#G-SIGNAL-DETAILED:CAPS">Has Details</a></p>
 </div>
 <hr>
 <div class="refsect2">
 <a name="GstBus-sync-message"></a><h3>The <code class="literal">“sync-message”</code> signal</h3>
 <pre class="programlisting"><span class="returnvalue">void</span>
 user_function (<a class="link" href="GstBus.html" title="GstBus"><span class="type">GstBus</span></a>     *bus,
                <a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a> *message,
                <a href="https://developer.gnome.org/glib/unstable/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a>    user_data)</pre>
 <p>A message has been posted on the bus. This signal is emitted from the
 thread that posted the message so one has to be careful with locking.</p>
 <p>This signal will not be emitted by default, you have to call
 <a class="link" href="GstBus.html#gst-bus-enable-sync-message-emission" title="gst_bus_enable_sync_message_emission ()"><code class="function">gst_bus_enable_sync_message_emission()</code></a> before.</p>
 <div class="refsect3">
 <a name="id-1.3.10.13.3.6"></a><h4>Parameters</h4>
 <div class="informaltable"><table width="100%" border="0">
 <colgroup>
 <col width="150px" class="parameters_name">
 <col class="parameters_description">
 <col width="200px" class="parameters_annotations">
 </colgroup>
 <tbody>
 <tr>
 <td class="parameter_name"><p>bus</p></td>
 <td class="parameter_description"><p>the object which received the signal</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>message</p></td>
 <td class="parameter_description"><p>the message that has been posted synchronously</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 <tr>
 <td class="parameter_name"><p>user_data</p></td>
 <td class="parameter_description"><p>user data set when the signal handler was connected.</p></td>
 <td class="parameter_annotations"> </td>
 </tr>
 </tbody>
 </table></div>
 </div>
 <p>Flags: <a href="https://developer.gnome.org/gobject/unstable/gobject-Signals.html#G-SIGNAL-DETAILED:CAPS">Has Details</a></p>
 </div>
 </div>
 <div class="refsect1">
 <a name="GstBus.see-also"></a><h2>See Also</h2>
 <p><a class="link" href="GstMessage.html" title="GstMessage"><span class="type">GstMessage</span></a>, <a class="link" href="GstElement.html" title="GstElement"><span class="type">GstElement</span></a></p>
 </div>
 </div>
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