Possible deadlock bug in org.classpath.icedtea.pulseaudio.PulseAudioDataLine

[Chuck Ritola]

Hello.

There is a possible deadlock bug between the PulseAudio Eventloop Thread
and outside threads when invoking PulseAudioDataLine.stop() and possibly
others. The issue appears to be rooted in the locking order being reversed
between close() and EventLoop.run().

close() locks the PulseAudioDataLine ending in 0490 first before attempting
to lock the Object ending in 4380 inside of EventLoop.

However, the EventLoop locks the Object 4380 first before attempting to
lock  the PulseAudioDataLine ending in 0490.

This creates opportunity for deadlock which I confirm occurs on occasion. I
wish I could provide deeper detail but I am having trouble finding the
source for this in the ubuntu openjdk-8-source package.

Using ubuntu package openjdk-8-jdk 8u121-b13-0ubuntu1.16.04.2

Below is a truncated thread dump from VisualVM:

Found one Java-level deadlock:
=============================
"PulseAudio Eventloop Thread":
  waiting to lock monitor 0x00007fb0c4508538 (object 0x00000000e4640490, a
org.classpath.icedtea.pulseaudio.PulseAudioSourceDataLine),
  which is held by "main"
"main":
  waiting to lock monitor 0x00007fb0c45085e8 (object 0x00000000e3be4380, a
java.lang.Object),
  which is held by "PulseAudio Eventloop Thread"

Java stack information for the threads listed above:
===================================================
"PulseAudio Eventloop Thread":
at
org.classpath.icedtea.pulseaudio.PulseAudioDataLine$3.update(PulseAudioDataLine.java:215)
- waiting to lock <0x00000000e4640490> (a
org.classpath.icedtea.pulseaudio.PulseAudioSourceDataLine)
at
org.classpath.icedtea.pulseaudio.Stream.playbackStartedCallback(Stream.java:688)
- locked <0x00000000e4640658> (a java.util.LinkedList)
at org.classpath.icedtea.pulseaudio.EventLoop.native_iterate(Native Method)
at org.classpath.icedtea.pulseaudio.EventLoop.run(EventLoop.java:133)
- locked <0x00000000e3be4380> (a java.lang.Object)
at java.lang.Thread.run(Thread.java:745)


"main":
at
org.classpath.icedtea.pulseaudio.PulseAudioDataLine.stop(PulseAudioDataLine.java:386)
- waiting to lock <0x00000000e3be4380> (a java.lang.Object)
- locked <0x00000000e4640490> (a
org.classpath.icedtea.pulseaudio.PulseAudioSourceDataLine)
at
org.classpath.icedtea.pulseaudio.PulseAudioSourceDataLine.stop(PulseAudioSourceDataLine.java:51)
at
[the rest is application-specific]
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