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comparison: src/share/vm/gc_implementation/g1/g1StringDedupQueue.hpp
src/share/vm/gc_implementation/g1/g1StringDedupQueue.hpp
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| 1 /* | |
| 2 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved. | |
| 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| 4 * | |
| 5 * This code is free software; you can redistribute it and/or modify it | |
| 6 * under the terms of the GNU General Public License version 2 only, as | |
| 7 * published by the Free Software Foundation. | |
| 8 * | |
| 9 * This code is distributed in the hope that it will be useful, but WITHOUT | |
| 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 12 * version 2 for more details (a copy is included in the LICENSE file that | |
| 13 * accompanied this code). | |
| 14 * | |
| 15 * You should have received a copy of the GNU General Public License version | |
| 16 * 2 along with this work; if not, write to the Free Software Foundation, | |
| 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| 18 * | |
| 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 20 * or visit www.oracle.com if you need additional information or have any | |
| 21 * questions. | |
| 22 * | |
| 23 */ | |
| 24 | |
| 25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP | |
| 26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP | |
| 27 | |
| 28 #include "memory/allocation.hpp" | |
| 29 #include "oops/oop.hpp" | |
| 30 #include "utilities/stack.hpp" | |
| 31 | |
| 32 class G1StringDedupUnlinkOrOopsDoClosure; | |
| 33 | |
| 34 // | |
| 35 // The deduplication queue acts as the communication channel between the stop-the-world | |
| 36 // mark/evacuation phase and the concurrent deduplication phase. Deduplication candidates | |
| 37 // found during mark/evacuation are placed on this queue for later processing in the | |
| 38 // deduplication thread. A queue entry is an oop pointing to a String object (as opposed | |
| 39 // to entries in the deduplication hashtable which points to character arrays). | |
| 40 // | |
| 41 // While users of the queue treat it as a single queue, it is implemented as a set of | |
| 42 // queues, one queue per GC worker thread, to allow lock-free and cache-friendly enqueue | |
| 43 // operations by the GC workers. | |
| 44 // | |
| 45 // The oops in the queue are treated as weak pointers, meaning the objects they point to | |
| 46 // can become unreachable and pruned (cleared) before being popped by the deduplication | |
| 47 // thread. | |
| 48 // | |
| 49 // Pushing to the queue is thread safe (this relies on each thread using a unique worker | |
| 50 // id), but only allowed during a safepoint. Popping from the queue is NOT thread safe | |
| 51 // and can only be done by the deduplication thread outside a safepoint. | |
| 52 // | |
| 53 // The StringDedupQueue_lock is only used for blocking and waking up the deduplication | |
| 54 // thread in case the queue is empty or becomes non-empty, respectively. This lock does | |
| 55 // not otherwise protect the queue content. | |
| 56 // | |
| 57 class G1StringDedupQueue : public CHeapObj<mtGC> { | |
| 58 private: | |
| 59 typedef Stack<oop, mtGC> G1StringDedupWorkerQueue; | |
| 60 | |
| 61 static G1StringDedupQueue* _queue; | |
| 62 static const size_t _max_size; | |
| 63 static const size_t _max_cache_size; | |
| 64 | |
| 65 G1StringDedupWorkerQueue* _queues; | |
| 66 size_t _nqueues; | |
| 67 size_t _cursor; | |
| 68 volatile bool _empty; | |
| 69 | |
| 70 // Statistics counter, only used for logging. | |
| 71 uintx _dropped; | |
| 72 | |
| 73 G1StringDedupQueue(); | |
| 74 ~G1StringDedupQueue(); | |
| 75 | |
| 76 static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue); | |
| 77 | |
| 78 public: | |
| 79 static void create(); | |
| 80 | |
| 81 // Blocks and waits for the queue to become non-empty. | |
| 82 static void wait(); | |
| 83 | |
| 84 // Pushes a deduplication candidate onto a specific GC worker queue. | |
| 85 static void push(uint worker_id, oop java_string); | |
| 86 | |
| 87 // Pops a deduplication candidate from any queue, returns NULL if | |
| 88 // all queues are empty. | |
| 89 static oop pop(); | |
| 90 | |
| 91 static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl); | |
| 92 | |
| 93 static void print_statistics(outputStream* st); | |
| 94 static void verify(); | |
| 95 }; | |
| 96 | |
| 97 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP |
