RFR: 8072701: resume001 failed due to ERROR: timeout for waiting for a BreakpintEvent [v2]

[Chris Plummer]

> The test hits a breakpoint on thread2 with SUSPEND_EVENT_THREAD policy, so only thread2 is suspended. It then does a vm.suspend(), which suspends all threads and bumps the suspendCount of thread2 up to 2. It then does an eventSet.resume(), which decrements the thread2 suspendCount to 1, so now all threads are suspended with a suspendCount of 1. thread2 is then resumed and we expect to hit the next thread2 breakpoint. The problem is that thread2 can't hit the breakpoint until the main thread has proceeded far enough, and if the vm.suspend() that suspended the main thread happens too quickly, it won't have proceeded far enough, so thread2 never hits the breakpoint.
> 
> Essentially we need a vm.resume() to allow the main thread to run, but we need to do it in a way that does nullify part of what the test is testing for. So in order to allow the vm.resume() but not subvert the intent of the test, we first do a thread2.suspend() so the vm.resume() won't resume thread2.
> 
> Testing in progress: tier1 and tier5 svc testing

Chris Plummer has updated the pull request incrementally with two additional commits since the last revision:

 - New solution. Use a sync point to force debugger to wait until mainThread is no longer doing a println()
 - Make printThreadsInfo() public so tests can call it.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20088/files
  - new: https://git.openjdk.org/jdk/pull/20088/files/b70bcd19..a5d0abc1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20088&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20088&range=00-01

  Stats: 40 lines in 3 files changed: 26 ins; 10 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/20088.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20088/head:pull/20088

PR: https://git.openjdk.org/jdk/pull/20088