1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000 1.2 +++ b/src/share/vm/gc_implementation/g1/g1StringDedupQueue.hpp Wed Apr 27 01:25:04 2016 +0800 1.3 @@ -0,0 +1,101 @@ 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 + bool _cancel; 1.72 + volatile bool _empty; 1.73 + 1.74 + // Statistics counter, only used for logging. 1.75 + uintx _dropped; 1.76 + 1.77 + G1StringDedupQueue(); 1.78 + ~G1StringDedupQueue(); 1.79 + 1.80 + static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue); 1.81 + 1.82 +public: 1.83 + static void create(); 1.84 + 1.85 + // Blocks and waits for the queue to become non-empty. 1.86 + static void wait(); 1.87 + 1.88 + // Wakes up any thread blocked waiting for the queue to become non-empty. 1.89 + static void cancel_wait(); 1.90 + 1.91 + // Pushes a deduplication candidate onto a specific GC worker queue. 1.92 + static void push(uint worker_id, oop java_string); 1.93 + 1.94 + // Pops a deduplication candidate from any queue, returns NULL if 1.95 + // all queues are empty. 1.96 + static oop pop(); 1.97 + 1.98 + static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl); 1.99 + 1.100 + static void print_statistics(outputStream* st); 1.101 + static void verify(); 1.102 +}; 1.103 + 1.104 +#endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP