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

[serguei.spitsyn at oracle.com]

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.

   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