Mercurial > hg > truffle
comparison src/share/vm/gc_implementation/g1/g1StringDedupQueue.hpp @ 17764:595c0f60d50d
8029075: String deduplication in G1
Summary: Implementation of JEP 192, http://openjdk.java.net/jeps/192
Reviewed-by: brutisso, tschatzl, coleenp
author | pliden |
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date | Tue, 18 Mar 2014 19:07:22 +0100 |
parents | |
children | 1772223a25a2 |
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17763:6e7e363c5a8f | 17764:595c0f60d50d |
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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 |