1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/gc_implementation/g1/g1StringDedupQueue.hpp Tue Mar 18 19:07:22 2014 +0100
1.3 @@ -0,0 +1,97 @@
1.4 +/*
1.5 + * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation.
1.11 + *
1.12 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.13 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.14 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.15 + * version 2 for more details (a copy is included in the LICENSE file that
1.16 + * accompanied this code).
1.17 + *
1.18 + * You should have received a copy of the GNU General Public License version
1.19 + * 2 along with this work; if not, write to the Free Software Foundation,
1.20 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.21 + *
1.22 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.23 + * or visit www.oracle.com if you need additional information or have any
1.24 + * questions.
1.25 + *
1.26 + */
1.27 +
1.28 +#ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP
1.29 +#define SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP
1.30 +
1.31 +#include "memory/allocation.hpp"
1.32 +#include "oops/oop.hpp"
1.33 +#include "utilities/stack.hpp"
1.34 +
1.35 +class G1StringDedupUnlinkOrOopsDoClosure;
1.36 +
1.37 +//
1.38 +// The deduplication queue acts as the communication channel between the stop-the-world
1.39 +// mark/evacuation phase and the concurrent deduplication phase. Deduplication candidates
1.40 +// found during mark/evacuation are placed on this queue for later processing in the
1.41 +// deduplication thread. A queue entry is an oop pointing to a String object (as opposed
1.42 +// to entries in the deduplication hashtable which points to character arrays).
1.43 +//
1.44 +// While users of the queue treat it as a single queue, it is implemented as a set of
1.45 +// queues, one queue per GC worker thread, to allow lock-free and cache-friendly enqueue
1.46 +// operations by the GC workers.
1.47 +//
1.48 +// The oops in the queue are treated as weak pointers, meaning the objects they point to
1.49 +// can become unreachable and pruned (cleared) before being popped by the deduplication
1.50 +// thread.
1.51 +//
1.52 +// Pushing to the queue is thread safe (this relies on each thread using a unique worker
1.53 +// id), but only allowed during a safepoint. Popping from the queue is NOT thread safe
1.54 +// and can only be done by the deduplication thread outside a safepoint.
1.55 +//
1.56 +// The StringDedupQueue_lock is only used for blocking and waking up the deduplication
1.57 +// thread in case the queue is empty or becomes non-empty, respectively. This lock does
1.58 +// not otherwise protect the queue content.
1.59 +//
1.60 +class G1StringDedupQueue : public CHeapObj<mtGC> {
1.61 +private:
1.62 + typedef Stack<oop, mtGC> G1StringDedupWorkerQueue;
1.63 +
1.64 + static G1StringDedupQueue* _queue;
1.65 + static const size_t _max_size;
1.66 + static const size_t _max_cache_size;
1.67 +
1.68 + G1StringDedupWorkerQueue* _queues;
1.69 + size_t _nqueues;
1.70 + size_t _cursor;
1.71 + volatile bool _empty;
1.72 +
1.73 + // Statistics counter, only used for logging.
1.74 + uintx _dropped;
1.75 +
1.76 + G1StringDedupQueue();
1.77 + ~G1StringDedupQueue();
1.78 +
1.79 + static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue);
1.80 +
1.81 +public:
1.82 + static void create();
1.83 +
1.84 + // Blocks and waits for the queue to become non-empty.
1.85 + static void wait();
1.86 +
1.87 + // Pushes a deduplication candidate onto a specific GC worker queue.
1.88 + static void push(uint worker_id, oop java_string);
1.89 +
1.90 + // Pops a deduplication candidate from any queue, returns NULL if
1.91 + // all queues are empty.
1.92 + static oop pop();
1.93 +
1.94 + static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl);
1.95 +
1.96 + static void print_statistics(outputStream* st);
1.97 + static void verify();
1.98 +};
1.99 +
1.100 +#endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP
