1.1 --- a/src/share/vm/runtime/mutex.cpp Tue Dec 06 18:28:51 2011 -0500
1.2 +++ b/src/share/vm/runtime/mutex.cpp Wed Dec 07 16:47:08 2011 -0500
1.3 @@ -527,7 +527,21 @@
1.4
1.5 void Monitor::IUnlock (bool RelaxAssert) {
1.6 assert (ILocked(), "invariant") ;
1.7 - _LockWord.Bytes[_LSBINDEX] = 0 ; // drop outer lock
1.8 + // Conceptually we need a MEMBAR #storestore|#loadstore barrier or fence immediately
1.9 + // before the store that releases the lock. Crucially, all the stores and loads in the
1.10 + // critical section must be globally visible before the store of 0 into the lock-word
1.11 + // that releases the lock becomes globally visible. That is, memory accesses in the
1.12 + // critical section should not be allowed to bypass or overtake the following ST that
1.13 + // releases the lock. As such, to prevent accesses within the critical section
1.14 + // from "leaking" out, we need a release fence between the critical section and the
1.15 + // store that releases the lock. In practice that release barrier is elided on
1.16 + // platforms with strong memory models such as TSO.
1.17 + //
1.18 + // Note that the OrderAccess::storeload() fence that appears after unlock store
1.19 + // provides for progress conditions and succession and is _not related to exclusion
1.20 + // safety or lock release consistency.
1.21 + OrderAccess::release_store(&_LockWord.Bytes[_LSBINDEX], 0); // drop outer lock
1.22 +
1.23 OrderAccess::storeload ();
1.24 ParkEvent * const w = _OnDeck ;
1.25 assert (RelaxAssert || w != Thread::current()->_MutexEvent, "invariant") ;
