--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/g1/g1StringDedupQueue.hpp	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,101 @@
+/*
+ * 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