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<base href="https://bugs.freedesktop.org/" />
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<th>Priority</th>
<td>medium
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - pa_threaded_mainloop_stop() blocks on pa_mutex_lock(m->mutex)"
href="https://bugs.freedesktop.org/show_bug.cgi?id=62529">62529</a>
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<th>CC</th>
<td>lennart@poettering.net
</td>
</tr>
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<th>Assignee</th>
<td>pulseaudio-bugs@lists.freedesktop.org
</td>
</tr>
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<th>Summary</th>
<td>pa_threaded_mainloop_stop() blocks on pa_mutex_lock(m->mutex)
</td>
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<th>QA Contact</th>
<td>pulseaudio-bugs@lists.freedesktop.org
</td>
</tr>
<tr>
<th>Severity</th>
<td>major
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
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<th>OS</th>
<td>Linux (All)
</td>
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<th>Reporter</th>
<td>changyp6@gmail.com
</td>
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<th>Hardware</th>
<td>ARM
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Component</th>
<td>clients
</td>
</tr>
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<th>Product</th>
<td>PulseAudio
</td>
</tr></table>
<p>
<div>
<pre>I recently switched my pulseaudio code to pulseaudio-3.0 and used
pa_threaded_mainloop to use pulseaudio library in multi-threaded application.
I find in some cases, pa_threaded_mainloop_stop() will just block on
pa_mutex_lock(m->mutex) and never quit.
I have read the source code of pa_threaded_mainloop_stop()
pa_threaded_mainloop_run(), it seems that there is one possibility that makes
this happen.
In pa_threaded_mainloop_run(), a thread is created and pa_mainloop_run is
called and protected by pa_mutex_lock(m->mutex) and pa_mutex_unlock(m->mutex)
in the thread;
in pa_threaded_mainloop_stop(), pa_mainloop_quit is also protected by
pa_mutex_lock(m->mutex) and pa_mutex_unlock(m->mutex);
So, here is the problem, in pa_threaded_mainloop_stop(), m->mutex must be
aquired before pa_mainloop_quit() can be called, and in
pa_threaded_mainloop_run(), when pa_mainloop_run() exits, m->mutex can be
unlocked. If pa_mainloop_run() is blocked, the only way to make
pa_mainloop_run() exit is to call pa_mainloop_quit(), but pa_mainloop_quit()
can only be called after pa_mainloop_run() is quit.
This is the deadlock.
I noticed that the mutex is created with flag RECURSIVE, which only makes this
mutex can be locked recursively in the same thread. In my case,
pa_threaded_mainloop_stop() is called from another thread, so the mutex still
can block pa_threaded_mainloop_stop().
This is easy to reproduce, use pa_threaded_mainloop() to write a recording
program, and start/stop repeatedly, sometimes pa_threaded_mainloop_stop() is
deadlocked.</pre>
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