Eclipse MAT shows no stack for many threads

Question

I have a leak in my code, and I've got a memory dump that I'm looking at with the awesome Eclipse Memory Analyzer tool.

Using the Thread_Overview, I can see that I have too many threads. However, only a few show stacks. The bulk of them (which are probably my leaks) show a status of 2 (BLOCKED), yet have no stacks.

Any idea what it means when there's no stack in the dump? Perhaps the thread is dead, but the reference is still kept in memory (ie. a leak)?

(Java 6 on Windows 2K if if makes any difference)

score 2 · Accepted Answer · answered Nov 10 '15 at 21:26

It means the thread has terminated. That's why no stack.

What threw me was this: the status of 2 is NOT blocked, but terminated. This is because the field threadStatus is a bit field that's decoded by sun.misc.VM.toThreadState(). I thought threadStatus was the thread state enum, but it's not. You have to read that method to see what the real state is. On windows, it's this:

public static Thread.State toThreadState(int paramInt)
{
 if ((paramInt & 0x4) != 0)
   return Thread.State.RUNNABLE;
 if ((paramInt & 0x400) != 0)
   return Thread.State.BLOCKED;
 if ((paramInt & 0x10) != 0)
   return Thread.State.WAITING;
 if ((paramInt & 0x20) != 0)
   return Thread.State.TIMED_WAITING;
 if ((paramInt & 0x2) != 0)
   return Thread.State.TERMINATED;
 if ((paramInt & 0x1) == 0) {
   return Thread.State.NEW;
 }
 return Thread.State.RUNNABLE;
}

So, the when threadStatus is 2, it means the thread's been terminated.

Eclipse MAT shows no stack for many threads

1 Answers1