Code review request: 8002273 NMT to report JNI memory leaks when -Xcheck:jni is on

[David Holmes]

Hi Zhengyu,

On 9/11/2012 3:23 AM, Zhengyu Gu wrote:
> This fix is related to JDK-8001743: Overlapped thread stacks. The cause
> of 8001743 is that, an attached JNI thread exited without detaching the
> thread, so JVM will leak a JavaThread object that attached to the JNI
> thread.
>
> The patch allows NMT to report such case when -Xcheck:jni VM option is
> specified.
>
> http://cr.openjdk.java.net/~zgu/8002273/webrev.00/

I'm a little unclear who is doing the checking here. Is it the case that 
a regular thread while updating its NMT records, detects that there is 
an overlap with an existing region, and infers from that that the other 
region must belong to a thread that failed to detach?

This comment doesn't read clearly to me, and we don't generally include 
references to bug reports:

  138   // an attached JNI thread can exit without detaching the thread, 
that results
  139   // JVM to leak JavaThread object (JDK-8001743)


If my understanding of the check is correct then to me a clearer comment 
would be:

// Overlapping stack regions indicate that a JNI thread failed to
// detach from the VM before exiting. This leaks the JavaThread object.

Cheers,
David

> Thanks,
>
> -Zhengyu