RFR (S) 8049304: race between VM_Exit and _sync_FutileWakeups->inc()

[Daniel D. Daugherty]

Greetings,

I have a "fix" for a long standing race between JVM shutdown and the
JVM statistics subsystem:

JDK-8049304 race between VM_Exit and _sync_FutileWakeups->inc()
https://bugs.openjdk.java.net/browse/JDK-8049304

Webrev URL: http://cr.openjdk.java.net/~dcubed/8049304-webrev/0-jdk9-hs-rt/

Testing: Aurora Adhoc RT-SVC nightly batch
          Aurora Adhoc vm.tmtools batch
          Kim's repro sequence for JDK-8049304
          Kim's repro sequence for JDK-8129978
          JPRT -testset hotspot

This "fix":

- adds a volatile flag to record whether PerfDataManager is holding
   data (PerfData objects)
- adds PerfDataManager::has_PerfData() to return the flag
- changes the Java monitor subsystem's use of PerfData to
   check both allocation of the monitor subsystem specific
   PerfData object and the new PerfDataManager::has_PerfData()
   return value

If the global 'UsePerfData' option is false, the system works as
it did before. If 'UsePerfData' is true (the default on non-embedded
systems), the Java monitor subsystem will allocate a number of
PerfData objects to record information. The objects will record
information about Java monitor subsystem until the JVM shuts down.

When the JVM starts to shutdown, the new PerfDataManager flag will
change to false and the Java monitor subsystem will stop using the
PerfData objects. This is the new behavior. As noted in the comments
I added to the code, the race is still present; I'm just changing
the order and the timing to reduce the likelihood of the crash.

Thanks, in advance, for any comments, questions or suggestions.

Dan