RFR: 8285032: [LOOM] vmTestbase/nsk/jdi/EventSet/suspendPolicy/suspendpolicy008/ fails with "eventSet.suspendPolicy() != policyExpected"

[Chris Plummer]

The test is testing that EventSets for ThreadStartEvents have the proper suspendPolicy. When there is more than one ThreadStartRequest and a thread is started, each ThreadStartRequest results in a ThreadStartEvent being created, and they all are grouped into the same EventSet. The suspendPolicy on this EventSet should come from the ThreadStartRequest suspend policy that suspends the most threads. The test is testing for all possible combinations of the 3 suspend polices (NONE, THREAD, and ALL). For example, if NONE and ALL are used, the resulting suspend policy should be ALL.

The following 3 issues are being addressed. These all turned up in loom as a result of carrier threads being created while the test was running, but potentially could happen with other threads that the jvm starts up.

1. When the test calls getEventSet() for the next ThreadStartEvent, it sometimes gets one that is for a carrier thread. In general this is not a problem because the test will accept any thread, but sometimes this carrier thread is generated between setting up two different `ThreadStartRequests`, and as a result has the wrong suspend policy, so the test fails with:

 nsk.share.TestFailure: ##> debugger: ERROR: eventSet.suspendPolicy() != policyExpected 

This is fixed by using getEventSetForThreadStartDeath(<threadName>) instead of getEventSet(), so carrier threads (and any other spuriously created thread) can be ignored.

2. The ThreadStartRequests used a filterCount of 1, which meant they would only produce one ThreadStartEvent. This meant that after fix (1) was in place, I started seeing issues with not even seeing the expected ThreadStartEvent, because the 1 count was used up by the carrier thread starting. I don't see any reason for this filterCount (other than the issue described in 3), so I just removed it.

3. After (1) and (2) were in place, I then noticed issues with sometimes getting a ThreadStartEvent when the BreakpointEvent was expected. This is because sometime a carrier thread was being created after receiving the expected ThreadStartEvent, but before the ThreadStartRequests could be disabled (this is the result of getting rid of the counterFiler). This was fixed by having breakpointForCommunication() filter out unexpected ThreadStartEvents by calling EventFilters.filtered(). I also had to add carrier threads that EventFilters.filtered() filters out.

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Commit messages:
 - Fix numerous issues with suspendPolicy008 related to unexpected thread creation.

Changes: https://git.openjdk.java.net/jdk/pull/8350/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8350&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285032
  Stats: 32 lines in 3 files changed: 14 ins; 2 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8350.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8350/head:pull/8350

PR: https://git.openjdk.java.net/jdk/pull/8350