I got a thread dump of one of my processes. It has a bunch of these threads. I guess they are keeping a bunch of memory so I am getting OOM.

"Thread-8264" prio=6 tid=0x4c94ac00 nid=0xf3c runnable [0x4fe7f000]
java.lang.Thread.State: RUNNABLE
at java.util.zip.Inflater.inflateBytes(Native Method)
at java.util.zip.Inflater.inflate(Inflater.java:223)
- locked <0x0c9bc640> (a java.util.zip.Inflater)
at org.apache.commons.compress.archivers.zip.ZipArchiveInputStream.read(ZipArchiveInputStream.java:235)
at com.my.ZipExtractorCommonsCompress.extract(ZipExtractorCommonsCompress.java:48)
at com.my.CustomThreadedExtractorWrapper$ExtractionThread.run(CustomThreadedExtractorWrapper.java:151)

Locked ownable synchronizers: - None

"Thread-8241" prio=6 tid=0x4c94a400 nid=0xb8c runnable [0x4faef000]
java.lang.Thread.State: RUNNABLE
at java.util.zip.Inflater.inflateBytes(Native Method)
at java.util.zip.Inflater.inflate(Inflater.java:223)
- locked <0x0c36b808> (a java.util.zip.Inflater)
at org.apache.commons.compress.archivers.zip.ZipArchiveInputStream.read(ZipArchiveInputStream.java:235)
at com.my.ZipExtractorCommonsCompress.extract(ZipExtractorCommonsCompress.java:48)
at com.my.CustomThreadedExtractorWrapper$ExtractionThread.run(CustomThreadedExtractorWrapper.java:151)

Locked ownable synchronizers: - None

I am trying to find out how it arrived to this situation. CustomThreadedExtractorWrapper is a wrapper class that fires a thread to do some work (ExtractionThread, which uses ZipExtractorCommonsCompress to extract zip contents from a compressed stream). If the task is taking too long, ExtractionThread.interrupt(); is called to cancel the operation.

I can see in my logs that the cancellation happened 25 times. And I see 21 of these threads in my dump. My questions:

1. What is the status of these threads? Alive and running? Blocked somehow?
2. They did not die with .interrupt() apparently? Is there a sure way to really kill a thread?

3. What does really mean 'locked ' in the stack trace? Line 223 in Inflater.java is:

   public synchronized int inflate(byte[] b, int off, int len) { ... //return is line 223 return inflateBytes(b, off, len);
   }