pliden@6413: /*
pliden@6413:  * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
pliden@6413:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
pliden@6413:  *
pliden@6413:  * This code is free software; you can redistribute it and/or modify it
pliden@6413:  * under the terms of the GNU General Public License version 2 only, as
pliden@6413:  * published by the Free Software Foundation.
pliden@6413:  *
pliden@6413:  * This code is distributed in the hope that it will be useful, but WITHOUT
pliden@6413:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
pliden@6413:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
pliden@6413:  * version 2 for more details (a copy is included in the LICENSE file that
pliden@6413:  * accompanied this code).
pliden@6413:  *
pliden@6413:  * You should have received a copy of the GNU General Public License version
pliden@6413:  * 2 along with this work; if not, write to the Free Software Foundation,
pliden@6413:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
pliden@6413:  *
pliden@6413:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
pliden@6413:  * or visit www.oracle.com if you need additional information or have any
pliden@6413:  * questions.
pliden@6413:  *
pliden@6413:  */
pliden@6413: 
pliden@6413: #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP
pliden@6413: #define SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP
pliden@6413: 
pliden@6413: #include "memory/allocation.hpp"
pliden@6413: #include "oops/oop.hpp"
pliden@6413: #include "utilities/stack.hpp"
pliden@6413: 
pliden@6413: class G1StringDedupUnlinkOrOopsDoClosure;
pliden@6413: 
pliden@6413: //
pliden@6413: // The deduplication queue acts as the communication channel between the stop-the-world
pliden@6413: // mark/evacuation phase and the concurrent deduplication phase. Deduplication candidates
pliden@6413: // found during mark/evacuation are placed on this queue for later processing in the
pliden@6413: // deduplication thread. A queue entry is an oop pointing to a String object (as opposed
pliden@6413: // to entries in the deduplication hashtable which points to character arrays).
pliden@6413: //
pliden@6413: // While users of the queue treat it as a single queue, it is implemented as a set of
pliden@6413: // queues, one queue per GC worker thread, to allow lock-free and cache-friendly enqueue
pliden@6413: // operations by the GC workers.
pliden@6413: //
pliden@6413: // The oops in the queue are treated as weak pointers, meaning the objects they point to
pliden@6413: // can become unreachable and pruned (cleared) before being popped by the deduplication
pliden@6413: // thread.
pliden@6413: //
pliden@6413: // Pushing to the queue is thread safe (this relies on each thread using a unique worker
pliden@6413: // id), but only allowed during a safepoint. Popping from the queue is NOT thread safe
pliden@6413: // and can only be done by the deduplication thread outside a safepoint.
pliden@6413: //
pliden@6413: // The StringDedupQueue_lock is only used for blocking and waking up the deduplication
pliden@6413: // thread in case the queue is empty or becomes non-empty, respectively. This lock does
pliden@6413: // not otherwise protect the queue content.
pliden@6413: //
pliden@6413: class G1StringDedupQueue : public CHeapObj<mtGC> {
pliden@6413: private:
pliden@6413:   typedef Stack<oop, mtGC> G1StringDedupWorkerQueue;
pliden@6413: 
pliden@6413:   static G1StringDedupQueue* _queue;
pliden@6413:   static const size_t        _max_size;
pliden@6413:   static const size_t        _max_cache_size;
pliden@6413: 
pliden@6413:   G1StringDedupWorkerQueue*  _queues;
pliden@6413:   size_t                     _nqueues;
pliden@6413:   size_t                     _cursor;
pliden@6690:   bool                       _cancel;
pliden@6413:   volatile bool              _empty;
pliden@6413: 
pliden@6413:   // Statistics counter, only used for logging.
pliden@6413:   uintx                      _dropped;
pliden@6413: 
pliden@6413:   G1StringDedupQueue();
pliden@6413:   ~G1StringDedupQueue();
pliden@6413: 
pliden@6413:   static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue);
pliden@6413: 
pliden@6413: public:
pliden@6413:   static void create();
pliden@6413: 
pliden@6413:   // Blocks and waits for the queue to become non-empty.
pliden@6413:   static void wait();
pliden@6413: 
pliden@6690:   // Wakes up any thread blocked waiting for the queue to become non-empty.
pliden@6690:   static void cancel_wait();
pliden@6690: 
pliden@6413:   // Pushes a deduplication candidate onto a specific GC worker queue.
pliden@6413:   static void push(uint worker_id, oop java_string);
pliden@6413: 
pliden@6413:   // Pops a deduplication candidate from any queue, returns NULL if
pliden@6413:   // all queues are empty.
pliden@6413:   static oop pop();
pliden@6413: 
pliden@6413:   static void unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl);
pliden@6413: 
pliden@6413:   static void print_statistics(outputStream* st);
pliden@6413:   static void verify();
pliden@6413: };
pliden@6413: 
pliden@6413: #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUPQUEUE_HPP