(S) RFR: 8029453: java/util/concurrent/locks/ReentrantLock/TimeoutLockLoops.java failed by timeout

[David Holmes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8029453

Webrev: http://cr.openjdk.java.net/~dholmes/8029453/webrev/

The code introduced in 6900441 contained a bug in the code path for when 
WorkAroundNPTLTimedWaitHang was zero, and this was exposed by the change 
in 8130728 which made the default setting of WorkAroundNPTLTimedWaitHang 
zero.

In PlatformParker on Linux _cur_index tracks which pthread_cond object 
is currently in use by a waiting thread (one for relative-timed waits, 
the other for absolute-timed waits) and is set to -1 when the thread is 
not waiting. In the path now used by default we release the 
pthread_mutex_t and then pthread_cond_signal the condition variable at 
_cond[_cur_index]. But as soon as we release the mutex the waiting 
thread can resume execution (it may have timed-out and so not need the 
signal) and set _cur_index to -1. The signalling thread then signals 
_cond[-1] which does not contain a pthread_cond_t object. This can 
result in the pthread_cond_signal hanging, and potentially other 
consequences.

The fix is simple: save the correct index before unlocking the mutex.

The test: java/util/concurrent/locks/ReentrantLock/TimeoutLockLoops.java 
has been marked as failing intermittently (8133231) due to this and I 
will revert that as part of this fix, once that change reaches the hs-rt 
forest.

Thanks,
David