<Sound Dev> RFR: 8266421: Deadlock in Sound System

[Sergey Bylokhov]

In the fix for JDK-8207150 I have updated the synchronization of some code paths under one "lock", before that code was synchronized only on some threads and missing on others. Old review:
http://mail.openjdk.java.net/pipermail/sound-dev/2018-August/000650.html

That fix introduced this order of locks: "lock"->"synchronized(this)", I have checked other places and did not found where we use the opposite order. Unfortunately, one such place exists in the private subclass DirectClip.

I have checked both usages of synchronized which caused deadlock:
 - In the DirectClip class the method setMicrosecondPosition is marked as "synchronized" but it is unclear why. This method is implemented as a call to another public method setFramePosition which is not "synchronized" and use some internal synchronization. So I have removed this keyword.
 - In a few places we have the code like this:

        boolean sendEvents = false;
        synchronized (this) {
            if (this.started != started) {
                this.started = started;
                sendEvents = true;
            }
	}
        if (sendEvents) {.....

I doubt that this type of synchronization may help something - the fields are volatile and we use sendEvents flag after synchronisation block, so I removed it as well. Any thoughts?

-------------

Commit messages:
 - Initial fix
 - Update SetPositionHang.java
 - Create SetPositionHang.java

Changes: https://git.openjdk.java.net/jdk/pull/4141/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4141&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266421
  Stats: 128 lines in 4 files changed: 106 ins; 11 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4141.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4141/head:pull/4141

PR: https://git.openjdk.java.net/jdk/pull/4141