1.1 --- a/src/share/vm/gc_implementation/g1/ptrQueue.cpp Thu Jan 14 09:20:13 2010 -0800
1.2 +++ b/src/share/vm/gc_implementation/g1/ptrQueue.cpp Wed Jan 13 15:45:47 2010 -0800
1.3 @@ -73,7 +73,12 @@
1.4
1.5 void PtrQueue::locking_enqueue_completed_buffer(void** buf) {
1.6 assert(_lock->owned_by_self(), "Required.");
1.7 +
1.8 + // We have to unlock _lock (which may be Shared_DirtyCardQ_lock) before
1.9 + // we acquire DirtyCardQ_CBL_mon inside enqeue_complete_buffer as they
1.10 + // have the same rank and we may get the "possible deadlock" message
1.11 _lock->unlock();
1.12 +
1.13 qset()->enqueue_complete_buffer(buf);
1.14 // We must relock only because the caller will unlock, for the normal
1.15 // case.
1.16 @@ -140,7 +145,36 @@
1.17 // holding the lock if there is one).
1.18 if (_buf != NULL) {
1.19 if (_lock) {
1.20 - locking_enqueue_completed_buffer(_buf);
1.21 + assert(_lock->owned_by_self(), "Required.");
1.22 +
1.23 + // The current PtrQ may be the shared dirty card queue and
1.24 + // may be being manipulated by more than one worker thread
1.25 + // during a pause. Since the enqueuing of the completed
1.26 + // buffer unlocks the Shared_DirtyCardQ_lock more than one
1.27 + // worker thread can 'race' on reading the shared queue attributes
1.28 + // (_buf and _index) and multiple threads can call into this
1.29 + // routine for the same buffer. This will cause the completed
1.30 + // buffer to be added to the CBL multiple times.
1.31 +
1.32 + // We "claim" the current buffer by caching value of _buf in
1.33 + // a local and clearing the field while holding _lock. When
1.34 + // _lock is released (while enqueueing the completed buffer)
1.35 + // the thread that acquires _lock will skip this code,
1.36 + // preventing the subsequent the multiple enqueue, and
1.37 + // install a newly allocated buffer below.
1.38 +
1.39 + void** buf = _buf; // local pointer to completed buffer
1.40 + _buf = NULL; // clear shared _buf field
1.41 +
1.42 + locking_enqueue_completed_buffer(buf); // enqueue completed buffer
1.43 +
1.44 + // While the current thread was enqueuing the buffer another thread
1.45 + // may have a allocated a new buffer and inserted it into this pointer
1.46 + // queue. If that happens then we just return so that the current
1.47 + // thread doesn't overwrite the buffer allocated by the other thread
1.48 + // and potentially losing some dirtied cards.
1.49 +
1.50 + if (_buf != NULL) return;
1.51 } else {
1.52 if (qset()->process_or_enqueue_complete_buffer(_buf)) {
1.53 // Recycle the buffer. No allocation.
