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6915005: G1: Hang in PtrQueueSet::completed_buffers_list_length with gcl001

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When enqueuing a completed PtrQueue buffer, cache a local pointer to the buffer and clear the field in the PtrQueue prior to unlocking the mutex referenced by the _lock field and pass the cached local value to the enqueuing routine. This will prevent the same completed buffer being enqueued multiple times, which causes the hang.

Reviewed-by: ysr
This commit is contained in:
John Cuthbertson 2010-01-13 15:45:47 -08:00
parent da0750f0b2
commit 29a13dc105
2 changed files with 35 additions and 42 deletions
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36
hotspot/src/share/vm/gc_implementation/g1/ptrQueue.cpp
View File

@ -73,7 +73,12 @@ void PtrQueue::enqueue_known_active(void* ptr) {
void PtrQueue::locking_enqueue_completed_buffer(void** buf) {
assert(_lock->owned_by_self(), "Required.");
// We have to unlock _lock (which may be Shared_DirtyCardQ_lock) before
// we acquire DirtyCardQ_CBL_mon inside enqeue_complete_buffer as they
// have the same rank and we may get the "possible deadlock" message
_lock->unlock();
qset()->enqueue_complete_buffer(buf);
// We must relock only because the caller will unlock, for the normal
// case.
@ -140,7 +145,36 @@ void PtrQueue::handle_zero_index() {
// holding the lock if there is one).
if (_buf != NULL) {
if (_lock) {
locking_enqueue_completed_buffer(_buf);
assert(_lock->owned_by_self(), "Required.");
// The current PtrQ may be the shared dirty card queue and
// may be being manipulated by more than one worker thread
// during a pause. Since the enqueuing of the completed
// buffer unlocks the Shared_DirtyCardQ_lock more than one
// worker thread can 'race' on reading the shared queue attributes
// (_buf and _index) and multiple threads can call into this
// routine for the same buffer. This will cause the completed
// buffer to be added to the CBL multiple times.
// We "claim" the current buffer by caching value of _buf in
// a local and clearing the field while holding _lock. When
// _lock is released (while enqueueing the completed buffer)
// the thread that acquires _lock will skip this code,
// preventing the subsequent the multiple enqueue, and
// install a newly allocated buffer below.
void** buf = _buf; // local pointer to completed buffer
_buf = NULL; // clear shared _buf field
locking_enqueue_completed_buffer(buf); // enqueue completed buffer
// While the current thread was enqueuing the buffer another thread
// may have a allocated a new buffer and inserted it into this pointer
// queue. If that happens then we just return so that the current
// thread doesn't overwrite the buffer allocated by the other thread
// and potentially losing some dirtied cards.
if (_buf != NULL) return;
} else {
if (qset()->process_or_enqueue_complete_buffer(_buf)) {
// Recycle the buffer. No allocation.

41
hotspot/src/share/vm/gc_implementation/g1/ptrQueue.inline.hpp
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@ -1,41 +0,0 @@
/*
* Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*
*/
void PtrQueue::handle_zero_index() {
assert(0 == _index, "Precondition.");
// This thread records the full buffer and allocates a new one (while
// holding the lock if there is one).
void** buf = _buf;
_buf = qset()->allocate_buffer();
_sz = qset()->buffer_size();
_index = _sz;
assert(0 <= _index && _index <= _sz, "Invariant.");
if (buf != NULL) {
if (_lock) {
locking_enqueue_completed_buffer(buf);
} else {
qset()->enqueue_complete_buffer(buf);
}
}
}