--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/shared/stringdedup/stringDedupQueue.hpp	Thu Jun 14 09:59:21 2018 -0400
@@ -0,0 +1,112 @@
+/*
+ * Copyright (c) 2018, 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_SHARED_STRINGDEDUP_STRINGDEDUPQUEUE_HPP
+#define SHARE_VM_GC_SHARED_STRINGDEDUP_STRINGDEDUPQUEUE_HPP
+
+#include "memory/allocation.hpp"
+#include "oops/oop.hpp"
+
+class StringDedupUnlinkOrOopsDoClosure;
+
+//
+// The deduplication queue acts as the communication channel between 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). Popping from the queue is NOT thread safe and can only be done by the deduplication
+// thread outside a safepoint.
+//
+
+class StringDedupQueue : public CHeapObj<mtGC> {
+private:
+  static StringDedupQueue*   _queue;
+  static volatile size_t     _claimed_index;
+
+public:
+  template <typename Q>
+  static void create();
+
+  // Blocks and waits for the queue to become non-empty.
+  static inline void wait();
+
+  // Wakes up any thread blocked waiting for the queue to become non-empty.
+  static inline void cancel_wait();
+
+  // Pushes a deduplication candidate onto a specific GC worker queue.
+  static inline void push(uint worker_id, oop java_string);
+
+  // Pops a deduplication candidate from any queue, returns NULL if
+  // all queues are empty.
+  static inline oop pop();
+
+  static void unlink_or_oops_do(StringDedupUnlinkOrOopsDoClosure* cl);
+
+  static void print_statistics();
+  static void verify();
+
+  // GC support
+  static void gc_prologue();
+  static void gc_epilogue();
+
+protected:
+  static StringDedupQueue* const queue();
+
+  // Queue interface.
+
+  // Blocks and waits for the queue to become non-empty.
+  virtual void wait_impl() = 0;
+
+  // Wakes up any thread blocked waiting for the queue to become non-empty.
+  virtual void cancel_wait_impl() = 0;
+
+  // Pushes a deduplication candidate onto a specific GC worker queue.
+  virtual void push_impl(uint worker_id, oop java_string) = 0;
+
+  // Pops a deduplication candidate from any queue, returns NULL if
+  // all queues are empty.
+  virtual oop pop_impl() = 0;
+
+  virtual void unlink_or_oops_do_impl(StringDedupUnlinkOrOopsDoClosure* cl, size_t queue) = 0;
+
+  virtual void print_statistics_impl() = 0;
+  virtual void verify_impl() = 0;
+
+  virtual size_t num_queues() const = 0;
+
+  static size_t claim();
+};
+
+#endif // SHARE_VM_GC_SHARED_STRINGDEDUP_STRINGDEDUPQUEUE_HPP