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src/share/vm/gc_implementation/g1/g1StringDedupQueue.hpp@e7d0505c8a30 (annotated)
src/share/vm/gc_implementation/g1/g1StringDedupQueue.hpp
Fri, 10 Oct 2014 15:51:58 +0200
- author
- tschatzl
- date
- Fri, 10 Oct 2014 15:51:58 +0200
- changeset 7257
- e7d0505c8a30
- parent 6690
- 1772223a25a2
- child 6876
- 710a3c8b516e
- permissions
- -rw-r--r--
8059758: Footprint regressions with JDK-8038423
Summary: Changes in JDK-8038423 always initialize (zero out) virtual memory used for auxiliary data structures. This causes a footprint regression for G1 in startup benchmarks. This is because they do not touch that memory at all, so the operating system does not actually commit these pages. The fix is to, if the initialization value of the data structures matches the default value of just committed memory (=0), do not do anything.
Reviewed-by: jwilhelm, brutisso
| pliden@6413 | 1 | /* |
| pliden@6413 | 2 | * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved. |
| pliden@6413 | 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| pliden@6413 | 4 | * |
| pliden@6413 | 5 | * This code is free software; you can redistribute it and/or modify it |
| pliden@6413 | 6 | * under the terms of the GNU General Public License version 2 only, as |
| pliden@6413 | 7 | * published by the Free Software Foundation. |
| pliden@6413 | 8 | * |
| pliden@6413 | 9 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| pliden@6413 | 10 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| pliden@6413 | 11 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| pliden@6413 | 12 | * version 2 for more details (a copy is included in the LICENSE file that |
| pliden@6413 | 13 | * accompanied this code). |
| pliden@6413 | 14 | * |
| pliden@6413 | 15 | * You should have received a copy of the GNU General Public License version |
| pliden@6413 | 16 | * 2 along with this work; if not, write to the Free Software Foundation, |
| pliden@6413 | 17 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| pliden@6413 | 18 | * |
| pliden@6413 | 19 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| pliden@6413 | 20 | * or visit www.oracle.com if you need additional information or have any |
| pliden@6413 | 21 | * questions. |
| pliden@6413 | 22 | * |
| pliden@6413 | 23 | */ |
| pliden@6413 | 24 | |
| pliden@6413 | 25 | #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP |
| pliden@6413 | 26 | #define SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP |
| pliden@6413 | 27 | |
| pliden@6413 | 28 | #include "memory/allocation.hpp" |
| pliden@6413 | 29 | #include "oops/oop.hpp" |
| pliden@6413 | 30 | #include "utilities/stack.hpp" |
| pliden@6413 | 31 | |
| pliden@6413 | 32 | class G1StringDedupUnlinkOrOopsDoClosure; |
| pliden@6413 | 33 | |
| pliden@6413 | 34 | // |
| pliden@6413 | 35 | // The deduplication queue acts as the communication channel between the stop-the-world |
| pliden@6413 | 36 | // mark/evacuation phase and the concurrent deduplication phase. Deduplication candidates |
| pliden@6413 | 37 | // found during mark/evacuation are placed on this queue for later processing in the |
| pliden@6413 | 38 | // deduplication thread. A queue entry is an oop pointing to a String object (as opposed |
| pliden@6413 | 39 | // to entries in the deduplication hashtable which points to character arrays). |
| pliden@6413 | 40 | // |
| pliden@6413 | 41 | // While users of the queue treat it as a single queue, it is implemented as a set of |
| pliden@6413 | 42 | // queues, one queue per GC worker thread, to allow lock-free and cache-friendly enqueue |
| pliden@6413 | 43 | // operations by the GC workers. |
| pliden@6413 | 44 | // |
| pliden@6413 | 45 | // The oops in the queue are treated as weak pointers, meaning the objects they point to |
| pliden@6413 | 46 | // can become unreachable and pruned (cleared) before being popped by the deduplication |
| pliden@6413 | 47 | // thread. |
| pliden@6413 | 48 | // |
| pliden@6413 | 49 | // Pushing to the queue is thread safe (this relies on each thread using a unique worker |
| pliden@6413 | 50 | // id), but only allowed during a safepoint. Popping from the queue is NOT thread safe |
| pliden@6413 | 51 | // and can only be done by the deduplication thread outside a safepoint. |
| pliden@6413 | 52 | // |
| pliden@6413 | 53 | // The StringDedupQueue_lock is only used for blocking and waking up the deduplication |
| pliden@6413 | 54 | // thread in case the queue is empty or becomes non-empty, respectively. This lock does |
| pliden@6413 | 55 | // not otherwise protect the queue content. |
| pliden@6413 | 56 | // |
| pliden@6413 | 57 | class G1StringDedupQueue : public CHeapObj<mtGC> { |
| pliden@6413 | 58 | private: |
| pliden@6413 | 59 | typedef Stack<oop, mtGC> G1StringDedupWorkerQueue; |
| pliden@6413 | 60 | |
| pliden@6413 | 61 | static G1StringDedupQueue* _queue; |
| pliden@6413 | 62 | static const size_t _max_size; |
| pliden@6413 | 63 | static const size_t _max_cache_size; |
| pliden@6413 | 64 | |
| pliden@6413 | 65 | G1StringDedupWorkerQueue* _queues; |
| pliden@6413 | 66 | size_t _nqueues; |
| pliden@6413 | 67 | size_t _cursor; |
| pliden@6690 | 68 | bool _cancel; |
| pliden@6413 | 69 | volatile bool _empty; |
| pliden@6413 | 70 | |
| pliden@6413 | 71 | // Statistics counter, only used for logging. |
| pliden@6413 | 72 | uintx _dropped; |
| pliden@6413 | 73 | |
| pliden@6413 | 74 | G1StringDedupQueue(); |
| pliden@6413 | 75 | ~G1StringDedupQueue(); |
| pliden@6413 | 76 | |
| pliden@6413 | 77 | static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue); |
| pliden@6413 | 78 | |
| pliden@6413 | 79 | public: |
| pliden@6413 | 80 | static void create(); |
| pliden@6413 | 81 | |
| pliden@6413 | 82 | // Blocks and waits for the queue to become non-empty. |
| pliden@6413 | 83 | static void wait(); |
| pliden@6413 | 84 | |
| pliden@6690 | 85 | // Wakes up any thread blocked waiting for the queue to become non-empty. |
| pliden@6690 | 86 | static void cancel_wait(); |
| pliden@6690 | 87 | |
| pliden@6413 | 88 | // Pushes a deduplication candidate onto a specific GC worker queue. |
| pliden@6413 | 89 | static void push(uint worker_id, oop java_string); |
| pliden@6413 | 90 | |
| pliden@6413 | 91 | // Pops a deduplication candidate from any queue, returns NULL if |
| pliden@6413 | 92 | // all queues are empty. |
| pliden@6413 | 93 | static oop pop(); |
| pliden@6413 | 94 | |
| pliden@6413 | 95 | static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl); |
| pliden@6413 | 96 | |
| pliden@6413 | 97 | static void print_statistics(outputStream* st); |
| pliden@6413 | 98 | static void verify(); |
| pliden@6413 | 99 | }; |
| pliden@6413 | 100 | |
| pliden@6413 | 101 | #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP |
