RFR (XS) 6471769: Error: assert(_cur_stack_depth == count_frames(), "cur_stack_depth out of sync")

[David Holmes]

Hi Serguei,

On 1/02/2014 12:58 PM, serguei.spitsyn at oracle.com wrote:
> Please, review the fix for:
>    https://bugs.openjdk.java.net/browse/JDK-6471769
>
>
> Open webrev:
> http://cr.openjdk.java.net/~sspitsyn/webrevs/2014/hotspot/6471769-JVMTI-FRAME/
>
>
> Summary:
>
>    There is a general issue in the suspend equivalent condition mechanism:
>    Two subsequent calls to the JvmtiEnv::is_thread_fully_suspended() may
> return different results:
>      - 1-st: true
>      - 2-nd: false
>
>    This more generic suspend equivalent issue is covered by another bug:
>      https://bugs.openjdk.java.net/browse/JDK-6280037
>
>    The bug to fix in this review is a specific manifestation of the 6280037
>    in the JVMTI GetFrameCount() that has a big impact on the SQE nightly.
>    It is on the Test Stabilization radar (as well as the 6280037).
>    There are many tests intermittently failing because of this.
>
>    The webrev for review is a one-liner work around the 6280037 for the
> GetFrameCount().
>
>    The JVMTI GetFrameCount() spec tells:
>      "If this function is called for a thread actively executing
> bytecodes (for example,
>       not the current thread and not suspended), the information
> returned is transient."
>
>    So, it is Ok to call the GetFrameCount() for non-suspended target
> threads.
>    To achieve safety, the frame count for non-suspended threads is
> calculated at a safepoint.
>    It should be Ok and more safe to do the same for suspended threads as
> well.
>    There is no big performance impact because it is already on a slow path.
>    It is still important to avoid safepointing when the target thread is
> current.

This sounds completely reasonable - Reviewed.

I can't check at the moment whether VM_GetFrameCount properly checks for 
a live target thread?

David

>    The bug 6280037 should go out of the Test Stabilization radar (remove
> the svc-nightly label)
>    as the most of the impacted tests are covered by the 6471769.
>
>
> Testing:
>    In progress: nsk.jvmti, nsk.jdi, nsk.jdwp, impacted JTreg tests
>
>
> Thanks,
> Serguei
>