RFR: 8020875 java/lang/management/ThreadMXBean/ResetPeakThreadCount.java fails intermittently

[Jaroslav Bachorik]

The java/lang/management/ThreadMXBean/ResetPeakThreadCount.java test
seems to be failing intermittently.

The test checks the functionality of the
j.l.m.ThreadMXBean.resetPeakThreadCount() method. It does so by
capturing the current value of "getPeakThreadCount()", starting a
predefined number of the user threads, stopping them and resetting the
stored peak value and making sure the new peak equals to the number of
the actually running threads.

The main problem is that it is not possible to prevent JVM to start/stop
arbitrary system threads while executing the test. This might lead to
small variations of the reported peak (a short-lived system thread is
started while the batch of the user threads is running) or the expected
number of running threads (again, a short-lived system thread is started
at the moment the test asks for the number of running threads).

The patch does not fix those shortcomings as it is not really possible
to do given the nature of the JVM threading system. It rather tries to
relax the conditions while still maintaining the ability to detect
functional problems - eg. decreasing peak without explicitly resetting
it and reporting false number of threads.

The webrev is at:
http://cr.openjdk.java.net/~jbachorik/8020875/webrev.00

Thanks,

-JB-