102 lines
3.9 KiB
C++
102 lines
3.9 KiB
C++
/*
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* Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP
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#define SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP
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#include "memory/allocation.hpp"
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#include "oops/oop.hpp"
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#include "utilities/stack.hpp"
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class G1StringDedupUnlinkOrOopsDoClosure;
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//
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// The deduplication queue acts as the communication channel between the stop-the-world
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// mark/evacuation phase and the concurrent deduplication phase. Deduplication candidates
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// found during mark/evacuation are placed on this queue for later processing in the
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// deduplication thread. A queue entry is an oop pointing to a String object (as opposed
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// to entries in the deduplication hashtable which points to character arrays).
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//
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// While users of the queue treat it as a single queue, it is implemented as a set of
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// queues, one queue per GC worker thread, to allow lock-free and cache-friendly enqueue
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// operations by the GC workers.
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//
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// The oops in the queue are treated as weak pointers, meaning the objects they point to
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// can become unreachable and pruned (cleared) before being popped by the deduplication
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// thread.
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//
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// Pushing to the queue is thread safe (this relies on each thread using a unique worker
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// id), but only allowed during a safepoint. Popping from the queue is NOT thread safe
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// and can only be done by the deduplication thread outside a safepoint.
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//
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// The StringDedupQueue_lock is only used for blocking and waking up the deduplication
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// thread in case the queue is empty or becomes non-empty, respectively. This lock does
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// not otherwise protect the queue content.
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//
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class G1StringDedupQueue : public CHeapObj<mtGC> {
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private:
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typedef Stack<oop, mtGC> G1StringDedupWorkerQueue;
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static G1StringDedupQueue* _queue;
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static const size_t _max_size;
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static const size_t _max_cache_size;
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G1StringDedupWorkerQueue* _queues;
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size_t _nqueues;
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size_t _cursor;
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bool _cancel;
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volatile bool _empty;
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// Statistics counter, only used for logging.
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uintx _dropped;
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G1StringDedupQueue();
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~G1StringDedupQueue();
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static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue);
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public:
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static void create();
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// Blocks and waits for the queue to become non-empty.
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static void wait();
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// Wakes up any thread blocked waiting for the queue to become non-empty.
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static void cancel_wait();
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// Pushes a deduplication candidate onto a specific GC worker queue.
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static void push(uint worker_id, oop java_string);
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// Pops a deduplication candidate from any queue, returns NULL if
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// all queues are empty.
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static oop pop();
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static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl);
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static void print_statistics(outputStream* st);
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static void verify();
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};
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#endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP
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