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src/share/vm/gc_implementation/g1/g1StringDedupQueue.hpp@595c0f60d50d (annotated)

src/share/vm/gc_implementation/g1/g1StringDedupQueue.hpp

Tue, 18 Mar 2014 19:07:22 +0100

author

pliden

date

Tue, 18 Mar 2014 19:07:22 +0100

changeset 6413

595c0f60d50d

child 6690

1772223a25a2

permissions

-rw-r--r--

8029075: String deduplication in G1
Summary: Implementation of JEP 192, http://openjdk.java.net/jeps/192
Reviewed-by: brutisso, tschatzl, coleenp

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@6413	68	volatile bool _empty;
pliden@6413	69
pliden@6413	70	// Statistics counter, only used for logging.
pliden@6413	71	uintx _dropped;
pliden@6413	72
pliden@6413	73	G1StringDedupQueue();
pliden@6413	74	~G1StringDedupQueue();
pliden@6413	75
pliden@6413	76	static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue);
pliden@6413	77
pliden@6413	78	public:
pliden@6413	79	static void create();
pliden@6413	80
pliden@6413	81	// Blocks and waits for the queue to become non-empty.
pliden@6413	82	static void wait();
pliden@6413	83
pliden@6413	84	// Pushes a deduplication candidate onto a specific GC worker queue.
pliden@6413	85	static void push(uint worker_id, oop java_string);
pliden@6413	86
pliden@6413	87	// Pops a deduplication candidate from any queue, returns NULL if
pliden@6413	88	// all queues are empty.
pliden@6413	89	static oop pop();
pliden@6413	90
pliden@6413	91	static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl);
pliden@6413	92
pliden@6413	93	static void print_statistics(outputStream* st);
pliden@6413	94	static void verify();
pliden@6413	95	};
pliden@6413	96
pliden@6413	97	#endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP