| /* |
| * Copyright (c) 2014, 2015, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| * |
| */ |
| |
| #ifndef SHARE_VM_GC_G1_G1STRINGDEDUPQUEUE_HPP |
| #define SHARE_VM_GC_G1_G1STRINGDEDUPQUEUE_HPP |
| |
| #include "memory/allocation.hpp" |
| #include "oops/oop.hpp" |
| #include "utilities/stack.hpp" |
| |
| class G1StringDedupUnlinkOrOopsDoClosure; |
| |
| // |
| // The deduplication queue acts as the communication channel between the stop-the-world |
| // mark/evacuation phase and the concurrent deduplication phase. Deduplication candidates |
| // found during mark/evacuation are placed on this queue for later processing in the |
| // deduplication thread. A queue entry is an oop pointing to a String object (as opposed |
| // to entries in the deduplication hashtable which points to character arrays). |
| // |
| // While users of the queue treat it as a single queue, it is implemented as a set of |
| // queues, one queue per GC worker thread, to allow lock-free and cache-friendly enqueue |
| // operations by the GC workers. |
| // |
| // The oops in the queue are treated as weak pointers, meaning the objects they point to |
| // can become unreachable and pruned (cleared) before being popped by the deduplication |
| // thread. |
| // |
| // Pushing to the queue is thread safe (this relies on each thread using a unique worker |
| // id), but only allowed during a safepoint. Popping from the queue is NOT thread safe |
| // and can only be done by the deduplication thread outside a safepoint. |
| // |
| // The StringDedupQueue_lock is only used for blocking and waking up the deduplication |
| // thread in case the queue is empty or becomes non-empty, respectively. This lock does |
| // not otherwise protect the queue content. |
| // |
| class G1StringDedupQueue : public CHeapObj<mtGC> { |
| private: |
| typedef Stack<oop, mtGC> G1StringDedupWorkerQueue; |
| |
| static G1StringDedupQueue* _queue; |
| static const size_t _max_size; |
| static const size_t _max_cache_size; |
| |
| G1StringDedupWorkerQueue* _queues; |
| size_t _nqueues; |
| size_t _cursor; |
| bool _cancel; |
| volatile bool _empty; |
| |
| // Statistics counter, only used for logging. |
| uintx _dropped; |
| |
| G1StringDedupQueue(); |
| ~G1StringDedupQueue(); |
| |
| static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue); |
| |
| public: |
| static void create(); |
| |
| // Blocks and waits for the queue to become non-empty. |
| static void wait(); |
| |
| // Wakes up any thread blocked waiting for the queue to become non-empty. |
| static void cancel_wait(); |
| |
| // Pushes a deduplication candidate onto a specific GC worker queue. |
| static void push(uint worker_id, oop java_string); |
| |
| // Pops a deduplication candidate from any queue, returns NULL if |
| // all queues are empty. |
| static oop pop(); |
| |
| static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl); |
| |
| static void print_statistics(); |
| static void verify(); |
| }; |
| |
| #endif // SHARE_VM_GC_G1_G1STRINGDEDUPQUEUE_HPP |