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<div id="projectname">PulseAudio
 <span id="projectnumber">15.0</span>
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<div class="title">Event Subscription </div> </div>
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<div class="textblock"><h1><a class="anchor" id="overv_sec"></a>
Overview</h1>
<p>The application can be notified, asynchronously, whenever the internal layout of the server changes. Possible notifications are described in the <a class="el" href="def_8h.html#a6bedfa147a9565383f1f44642cfef6a3">pa_subscription_event_type</a> and <a class="el" href="def_8h.html#ad4e7f11f879e8c77ae5289145ecf6947">pa_subscription_mask</a> enumerations.</p>
<p>The application sets the notification mask using <a class="el" href="subscribe_8h.html#abe684246fd5cb640b0199bcfe7f801b0" title="Enable event notification.">pa_context_subscribe()</a> and the function that will be called whenever a notification occurs using <a class="el" href="subscribe_8h.html#a55281f798863e7b37594d347be7ad98c" title="Set the context specific call back function that is called whenever the state of the daemon changes.">pa_context_set_subscribe_callback()</a>.</p>
<p>The callback will be called with a <a class="el" href="def_8h.html#a22c992200357163b430362332a04ef43">pa_subscription_event_type_t</a> representing the event that caused the callback. Clients can examine what object changed using <a class="el" href="def_8h.html#a6bedfa147a9565383f1f44642cfef6a3a55fdfc2a2ca13b0356e1389b522f38f7">PA_SUBSCRIPTION_EVENT_FACILITY_MASK</a>. The actual event type can then be extracted with <a class="el" href="def_8h.html#a6bedfa147a9565383f1f44642cfef6a3aa79dc3715e76129204822efba5d49219">PA_SUBSCRIPTION_EVENT_TYPE_MASK</a>. Please note that the masked values are integers, not flags (so you will check the object/event type using a comparison not a binary AND). For example, the callback might look something like:</p>
<pre class="fragment">void my_subscription_callback(pa_context *c, pa_subscription_event_type_t t,
uint32_t idx, void *userdata) {
if ((t & PA_SUBSCRIPTION_EVENT_FACILITY_MASK) == PA_SUBSCRIPTION_EVENT_SOURCE) {
if ((t & PA_SUBSCRIPTION_EVENT_TYPE_MASK) == PA_SUBSCRIPTION_EVENT_NEW) {
... a source was added, let's do stuff! ...
}
}
}
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