--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/shared/suspendibleThreadSet.hpp	Wed Oct 18 21:17:46 2017 +0200
@@ -0,0 +1,119 @@
+/*
+ * Copyright (c) 2014, 2017, 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_GC_SHARED_SUSPENDIBLETHREADSET_HPP
+#define SHARE_GC_SHARED_SUSPENDIBLETHREADSET_HPP
+
+#include "memory/allocation.hpp"
+
+// A SuspendibleThreadSet is a set of threads that can be suspended.
+// A thread can join and later leave the set, and periodically yield.
+// If some thread (not in the set) requests, via synchronize(), that
+// the threads be suspended, then the requesting thread is blocked
+// until all the threads in the set have yielded or left the set. Threads
+// may not enter the set when an attempted suspension is in progress. The
+// suspending thread later calls desynchronize(), allowing the suspended
+// threads to continue.
+class SuspendibleThreadSet : public AllStatic {
+  friend class SuspendibleThreadSetJoiner;
+  friend class SuspendibleThreadSetLeaver;
+
+private:
+  static uint   _nthreads;
+  static uint   _nthreads_stopped;
+  static bool   _suspend_all;
+  static double _suspend_all_start;
+
+  static bool is_synchronized();
+
+  // Add the current thread to the set. May block if a suspension is in progress.
+  static void join();
+
+  // Removes the current thread from the set.
+  static void leave();
+
+public:
+  // Returns true if an suspension is in progress.
+  static bool should_yield() { return _suspend_all; }
+
+  // Suspends the current thread if a suspension is in progress.
+  static void yield();
+
+  // Returns when all threads in the set are suspended.
+  static void synchronize();
+
+  // Resumes all suspended threads in the set.
+  static void desynchronize();
+};
+
+class SuspendibleThreadSetJoiner : public StackObj {
+private:
+  bool _active;
+
+public:
+  SuspendibleThreadSetJoiner(bool active = true) : _active(active) {
+    if (_active) {
+      SuspendibleThreadSet::join();
+    }
+  }
+
+  ~SuspendibleThreadSetJoiner() {
+    if (_active) {
+      SuspendibleThreadSet::leave();
+    }
+  }
+
+  bool should_yield() {
+    if (_active) {
+      return SuspendibleThreadSet::should_yield();
+    } else {
+      return false;
+    }
+  }
+
+  void yield() {
+    assert(_active, "Thread has not joined the suspendible thread set");
+    SuspendibleThreadSet::yield();
+  }
+};
+
+class SuspendibleThreadSetLeaver : public StackObj {
+private:
+  bool _active;
+
+public:
+  SuspendibleThreadSetLeaver(bool active = true) : _active(active) {
+    if (_active) {
+      SuspendibleThreadSet::leave();
+    }
+  }
+
+  ~SuspendibleThreadSetLeaver() {
+    if (_active) {
+      SuspendibleThreadSet::join();
+    }
+  }
+};
+
+#endif // SHARE_GC_SHARED_SUSPENDIBLETHREADSET_HPP