title: What does "Number of locked synchronizers = 1" in a StackTrace mean?
body: <p>I am currently working on some code that I inherited. When executing it, a lot of exceptions get logged to the console, where one such exception would look like this:</p>
  
  <pre><code>["bg-thread-0" Id=28 RUNNABLE
      at java.util.zip.ZipFile.read(Native Method)
      at java.util.zip.ZipFile.access$1400(ZipFile.java:56)
      at java.util.zip.ZipFile$ZipFileInputStream.read(ZipFile.java:677)
      -  locked java.util.zip.ZipFile@67369c20
      at java.util.zip.ZipFile$ZipFileInflaterInputStream.fill(ZipFile.java:413)
      at java.util.zip.InflaterInputStream.read(InflaterInputStream.java:158)
      at org.eclipse.osgi.baseadaptor.bundlefile.BundleEntry.getBytes(BundleEntry.java:102)
      at org.eclipse.osgi.baseadaptor.loader.ClasspathManager.findClassImpl(ClasspathManager.java:511)
      at org.eclipse.osgi.baseadaptor.loader.ClasspathManager.findLocalClassImpl(ClasspathManager.java:455)
      ...
  
      Number of locked synchronizers = 1
      - java.util.concurrent.ThreadPoolExecutor$Worker@66e5b079
  
  ]
  </code></pre>
  
  <p>I am using <a href="http://logback.qos.ch" rel="nofollow">Logback</a> for the logging. Now I have no idea where that exception is generated or logged, because that information is cut by the <code>...</code>.
  I also have no idea what it means. I guess it's got something to do with deadlocks (because of the <code>Number of locked synchronizers = 1</code>), but I don't know for sure.</p>
  
  <p>So my question is: How to proceed here? What does that exception mean, how do I debug and find it and how do I resolve it? I really have no clue and would appreciate any hints. Thanks!</p>