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POWhat can cause IllegalMonitorStateException from inside a synchronized block?
 

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  1. POWhat can cause IllegalMonitorStateException from inside a synchronized block?
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    <p>We hit an extremely surprising exception today. Inside of a synchronized block, we call wait() and it throws <code>IllegalMonitorStateException</code>. What can cause this?</p> <p>This is happening in well-tested open source code: <a href="http://svn.apache.org/viewvc/river/jtsk/trunk/src/com/sun/jini/jeri/internal/mux/Mux.java?view=markup#l222">http://svn.apache.org/viewvc/river/jtsk/trunk/src/com/sun/jini/jeri/internal/mux/Mux.java?view=markup#l222</a></p> <p>We eliminated the obvious causes:</p> <ul> <li>are we synchronized on the right variable? Yes, it's <code>muxLock</code></li> <li>is it a mutable variable? No, <code>muxLock</code> is final</li> <li>are we using any weird "-XX:" JVM flags that might affect monitor behavior? No, but we are launching the JVM embedded inside a C++ app via JNI.</li> <li>is this a strange JVM? No, it's Sun's 1.6.0_25 win/x64 JRE</li> <li>is this a known JVM bug? Can't find anything relevant at <a href="http://bugs.sun.com/bugdatabase">http://bugs.sun.com/bugdatabase</a></li> </ul> <p>So, I'm trying to think of more far-fetched explanations.</p> <ul> <li>could an uncaught out-of-memory error cause the monitor state to be screwed up? We're looking at this, but we're seeing no evidence of memory errors yet.</li> </ul> <p><strong>UPDATE:</strong> (based on comment)</p> <p>I've also verified from the stacktrace and breakpoint that the thread is indeed inside the synchronized block when the exception is thrown. It's not the case that some other unrelated code is emitting the exception (unless something is REALLY confusing Eclipse!)</p>
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      1. POWhat can cause IllegalMonitorStateException from inside a synchronized block?
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    1. COIs it possible to edit the source and/or get at the underlying cause of the exception? See if it was thrown by a different piece of code, etc?
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      1. POWhat can cause IllegalMonitorStateException from inside a synchronized block?
      1. USChris Aldrich
    2. CO@ChrisAldrich - Good question. No, we caught the stack trace one of the times it happened. See this screen capture of Eclipse sitting on an uncaught exception breakpoint (sorry, should have grabbed the trace as as text...) http://i.imgur.com/UPPQS.png
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      1. POWhat can cause IllegalMonitorStateException from inside a synchronized block?
      1. USChris Dolan
    3. COIt does look like a bug, Java 6 update 26 came soon after update 25. I would try that.
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      1. USPeter Lawrey
 

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