<Sound Dev> [9] Review request for 8168751: Two "Direct Clip" threads are created to play the same "AudioClip" object, what makes clip sound corrupted

[Anton Litvinov]

Hello,

Could you please review the following fix for the bug.

Bug: https://bugs.openjdk.java.net/browse/JDK-8168751
Webrev: http://cr.openjdk.java.net/~alitvinov/8168751/jdk9/webrev.00

The bug consists in the fact that after many repetitive sequential calls 
to the methods "loop()", "stop()" on the same instance of 
"java.applet.AudioClip" at some moment two threads with the name "Direct 
Clip", which play this "AudioClip" instance, are created and start 
existing in parallel, what makes the being played clip sound as corrupted.

"Direct Clip" thread is represented by the instance variable 
"com.sun.media.sound.DirectAudioDevice.DirectClip.thread", is created in 
the method "com.sun.media.sound.DirectAudioDevice.DirectClip.open()" and 
is stopped by assigning "null" value to "DirectClip.thread" instance 
variable in the method 
"com.sun.media.sound.DirectAudioDevice.DirectClip.implClose()".

THE DEFINED ROOT CAUSES OF THE BUG:

1. The fact that "DirectClip.thread" instance variable is not 
thread-safe. There is a possibility that null value assigned to it in 
one thread through the former mentioned "DirectClip.implClose()" method 
does not become visible for the running "Direct Clip" thread in the 
method "DirectClip.run()".

2. In the method "DirectClip.run()" not taking into account the fact 
that a new "Direct Clip" thread could have already been started and 
assigned to "DirectClip.thread" instance variable after the call to 
"DirectClip.implClose()", by the moment when "DirectClip.thread" value 
is checked for null in "DirectClip.run()" method, or by the moment when 
the previous "Direct Clip" thread is awakened and continues execution 
after the following code block in "DirectClip.run()" from the file 
"jdk/src/java.desktop/share/classes/com/sun/media/sound/DirectAudioDevice.java".

1354                 try {
1355                     lock.wait();
1356 } catch(InterruptedException ie) {}


THE SOLUTION:
The solution is based on correction of the listed above 2 root causes of 
the bug.

Thank you,
Anton
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