--- a/make/hotspot/lib/JvmFeatures.gmk	Wed Oct 18 14:31:10 2017 +0200
+++ b/make/hotspot/lib/JvmFeatures.gmk	Wed Oct 18 21:17:46 2017 +0200
@@ -132,6 +132,7 @@
       cms/ g1/ parallel/
   JVM_EXCLUDE_FILES += \
       concurrentGCThread.cpp \
+      suspendibleThreadSet.cpp \
       plab.cpp
   JVM_EXCLUDE_FILES += \
       g1MemoryPool.cpp \

--- a/src/hotspot/share/gc/g1/concurrentG1RefineThread.cpp	Wed Oct 18 14:31:10 2017 +0200
+++ b/src/hotspot/share/gc/g1/concurrentG1RefineThread.cpp	Wed Oct 18 21:17:46 2017 +0200
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 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
@@ -27,7 +27,7 @@
 #include "gc/g1/concurrentG1RefineThread.hpp"
 #include "gc/g1/g1CollectedHeap.inline.hpp"
 #include "gc/g1/g1RemSet.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
 #include "logging/log.hpp"
 #include "memory/resourceArea.hpp"
 #include "runtime/handles.inline.hpp"

--- a/src/hotspot/share/gc/g1/concurrentMarkThread.cpp	Wed Oct 18 14:31:10 2017 +0200
+++ b/src/hotspot/share/gc/g1/concurrentMarkThread.cpp	Wed Oct 18 21:17:46 2017 +0200
@@ -30,12 +30,12 @@
 #include "gc/g1/g1ConcurrentMark.inline.hpp"
 #include "gc/g1/g1MMUTracker.hpp"
 #include "gc/g1/g1Policy.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
 #include "gc/g1/vm_operations_g1.hpp"
 #include "gc/shared/concurrentGCPhaseManager.hpp"
 #include "gc/shared/gcId.hpp"
 #include "gc/shared/gcTrace.hpp"
 #include "gc/shared/gcTraceTime.inline.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
 #include "logging/log.hpp"
 #include "memory/resourceArea.hpp"
 #include "runtime/vmThread.hpp"

--- a/src/hotspot/share/gc/g1/g1CardLiveData.cpp	Wed Oct 18 14:31:10 2017 +0200
+++ b/src/hotspot/share/gc/g1/g1CardLiveData.cpp	Wed Oct 18 21:17:46 2017 +0200
@@ -26,7 +26,7 @@
 #include "gc/g1/g1CollectedHeap.inline.hpp"
 #include "gc/g1/g1ConcurrentMark.inline.hpp"
 #include "gc/g1/g1CardLiveData.inline.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
 #include "gc/shared/workgroup.hpp"
 #include "logging/log.hpp"
 #include "memory/universe.hpp"

--- a/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Wed Oct 18 14:31:10 2017 +0200
+++ b/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Wed Oct 18 21:17:46 2017 +0200
@@ -57,7 +57,6 @@
 #include "gc/g1/heapRegion.inline.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
 #include "gc/g1/heapRegionSet.inline.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
 #include "gc/g1/vm_operations_g1.hpp"
 #include "gc/shared/gcHeapSummary.hpp"
 #include "gc/shared/gcId.hpp"
@@ -68,6 +67,7 @@
 #include "gc/shared/generationSpec.hpp"
 #include "gc/shared/isGCActiveMark.hpp"
 #include "gc/shared/preservedMarks.inline.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
 #include "gc/shared/referenceProcessor.inline.hpp"
 #include "gc/shared/taskqueue.inline.hpp"
 #include "logging/log.hpp"

--- a/src/hotspot/share/gc/g1/g1ConcurrentMark.cpp	Wed Oct 18 14:31:10 2017 +0200
+++ b/src/hotspot/share/gc/g1/g1ConcurrentMark.cpp	Wed Oct 18 21:17:46 2017 +0200
@@ -38,7 +38,6 @@
 #include "gc/g1/heapRegion.inline.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
 #include "gc/g1/heapRegionSet.inline.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
 #include "gc/shared/gcId.hpp"
 #include "gc/shared/gcTimer.hpp"
 #include "gc/shared/gcTrace.hpp"
@@ -46,6 +45,7 @@
 #include "gc/shared/genOopClosures.inline.hpp"
 #include "gc/shared/referencePolicy.hpp"
 #include "gc/shared/strongRootsScope.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
 #include "gc/shared/taskqueue.inline.hpp"
 #include "gc/shared/vmGCOperations.hpp"
 #include "logging/log.hpp"

--- a/src/hotspot/share/gc/g1/g1ConcurrentMark.inline.hpp	Wed Oct 18 14:31:10 2017 +0200
+++ b/src/hotspot/share/gc/g1/g1ConcurrentMark.inline.hpp	Wed Oct 18 21:17:46 2017 +0200
@@ -29,7 +29,7 @@
 #include "gc/g1/g1ConcurrentMark.hpp"
 #include "gc/g1/g1ConcurrentMarkBitMap.inline.hpp"
 #include "gc/g1/g1ConcurrentMarkObjArrayProcessor.inline.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
 #include "gc/shared/taskqueue.inline.hpp"
 #include "utilities/bitMap.inline.hpp"
 

--- a/src/hotspot/share/gc/g1/g1RemSet.cpp	Wed Oct 18 14:31:10 2017 +0200
+++ b/src/hotspot/share/gc/g1/g1RemSet.cpp	Wed Oct 18 21:17:46 2017 +0200
@@ -36,8 +36,8 @@
 #include "gc/g1/heapRegion.inline.hpp"
 #include "gc/g1/heapRegionManager.inline.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
 #include "gc/shared/gcTraceTime.inline.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
 #include "memory/iterator.hpp"
 #include "memory/resourceArea.hpp"
 #include "oops/oop.inline.hpp"

--- a/src/hotspot/share/gc/g1/g1StringDedupThread.cpp	Wed Oct 18 14:31:10 2017 +0200
+++ b/src/hotspot/share/gc/g1/g1StringDedupThread.cpp	Wed Oct 18 21:17:46 2017 +0200
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2016, Oracle and/or its affiliates. All rights reserved.
+ * 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
@@ -28,7 +28,7 @@
 #include "gc/g1/g1StringDedupQueue.hpp"
 #include "gc/g1/g1StringDedupTable.hpp"
 #include "gc/g1/g1StringDedupThread.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
 #include "logging/log.hpp"
 #include "oops/oop.inline.hpp"
 #include "runtime/atomic.hpp"

--- a/src/hotspot/share/gc/g1/g1YoungRemSetSamplingThread.cpp	Wed Oct 18 14:31:10 2017 +0200
+++ b/src/hotspot/share/gc/g1/g1YoungRemSetSamplingThread.cpp	Wed Oct 18 21:17:46 2017 +0200
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 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
@@ -29,7 +29,7 @@
 #include "gc/g1/g1YoungRemSetSamplingThread.hpp"
 #include "gc/g1/heapRegion.inline.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
 #include "runtime/mutexLocker.hpp"
 
 G1YoungRemSetSamplingThread::G1YoungRemSetSamplingThread() :

--- a/src/hotspot/share/gc/g1/suspendibleThreadSet.cpp	Wed Oct 18 14:31:10 2017 +0200
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,134 +0,0 @@
-/*
- * Copyright (c) 2014, 2016, 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.
- *
- */
-
-#include "precompiled.hpp"
-#include "gc/g1/suspendibleThreadSet.hpp"
-#include "runtime/mutexLocker.hpp"
-#include "runtime/semaphore.hpp"
-#include "runtime/thread.inline.hpp"
-
-uint   SuspendibleThreadSet::_nthreads          = 0;
-uint   SuspendibleThreadSet::_nthreads_stopped  = 0;
-bool   SuspendibleThreadSet::_suspend_all       = false;
-double SuspendibleThreadSet::_suspend_all_start = 0.0;
-
-static Semaphore* _synchronize_wakeup = NULL;
-
-void SuspendibleThreadSet_init() {
-  assert(_synchronize_wakeup == NULL, "STS already initialized");
-  _synchronize_wakeup = new Semaphore();
-}
-
-bool SuspendibleThreadSet::is_synchronized() {
-  assert_lock_strong(STS_lock);
-  assert(_nthreads_stopped <= _nthreads, "invariant");
-  return _nthreads_stopped == _nthreads;
-}
-
-void SuspendibleThreadSet::join() {
-  assert(!Thread::current()->is_suspendible_thread(), "Thread already joined");
-  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
-  while (_suspend_all) {
-    ml.wait(Mutex::_no_safepoint_check_flag);
-  }
-  _nthreads++;
-  DEBUG_ONLY(Thread::current()->set_suspendible_thread();)
-}
-
-void SuspendibleThreadSet::leave() {
-  assert(Thread::current()->is_suspendible_thread(), "Thread not joined");
-  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
-  assert(_nthreads > 0, "Invalid");
-  DEBUG_ONLY(Thread::current()->clear_suspendible_thread();)
-  _nthreads--;
-  if (_suspend_all && is_synchronized()) {
-    // This leave completes a request, so inform the requestor.
-    _synchronize_wakeup->signal();
-  }
-}
-
-void SuspendibleThreadSet::yield() {
-  assert(Thread::current()->is_suspendible_thread(), "Must have joined");
-  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
-  if (_suspend_all) {
-    _nthreads_stopped++;
-    if (is_synchronized()) {
-      if (ConcGCYieldTimeout > 0) {
-        double now = os::elapsedTime();
-        guarantee((now - _suspend_all_start) * 1000.0 < (double)ConcGCYieldTimeout, "Long delay");
-      }
-      // This yield completes the request, so inform the requestor.
-      _synchronize_wakeup->signal();
-    }
-    while (_suspend_all) {
-      ml.wait(Mutex::_no_safepoint_check_flag);
-    }
-    assert(_nthreads_stopped > 0, "Invalid");
-    _nthreads_stopped--;
-  }
-}
-
-void SuspendibleThreadSet::synchronize() {
-  assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
-  if (ConcGCYieldTimeout > 0) {
-    _suspend_all_start = os::elapsedTime();
-  }
-  {
-    MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
-    assert(!_suspend_all, "Only one at a time");
-    _suspend_all = true;
-    if (is_synchronized()) {
-      return;
-    }
-  } // Release lock before semaphore wait.
-
-  // Semaphore initial count is zero.  To reach here, there must be at
-  // least one not yielded thread in the set, e.g. is_synchronized()
-  // was false before the lock was released.  A thread in the set will
-  // signal the semaphore iff it is the last to yield or leave while
-  // there is an active suspend request.  So there will be exactly one
-  // signal, which will increment the semaphore count to one, which
-  // will then be consumed by this wait, returning it to zero.  No
-  // thread can exit yield or enter the set until desynchronize is
-  // called, so there are no further opportunities for the semaphore
-  // being signaled until we get back here again for some later
-  // synchronize call.  Hence, there is no need to re-check for
-  // is_synchronized after the wait; it will always be true there.
-  _synchronize_wakeup->wait();
-
-#ifdef ASSERT
-  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
-  assert(_suspend_all, "STS not synchronizing");
-  assert(is_synchronized(), "STS not synchronized");
-#endif
-}
-
-void SuspendibleThreadSet::desynchronize() {
-  assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
-  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
-  assert(_suspend_all, "STS not synchronizing");
-  assert(is_synchronized(), "STS not synchronized");
-  _suspend_all = false;
-  ml.notify_all();
-}

--- a/src/hotspot/share/gc/g1/suspendibleThreadSet.hpp	Wed Oct 18 14:31:10 2017 +0200
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,119 +0,0 @@
-/*
- * Copyright (c) 2014, 2016, 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_SUSPENDIBLETHREADSET_HPP
-#define SHARE_VM_GC_G1_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_VM_GC_G1_SUSPENDIBLETHREADSET_HPP

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/shared/suspendibleThreadSet.cpp	Wed Oct 18 21:17:46 2017 +0200
@@ -0,0 +1,134 @@
+/*
+ * 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.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
+#include "runtime/mutexLocker.hpp"
+#include "runtime/semaphore.hpp"
+#include "runtime/thread.inline.hpp"
+
+uint   SuspendibleThreadSet::_nthreads          = 0;
+uint   SuspendibleThreadSet::_nthreads_stopped  = 0;
+bool   SuspendibleThreadSet::_suspend_all       = false;
+double SuspendibleThreadSet::_suspend_all_start = 0.0;
+
+static Semaphore* _synchronize_wakeup = NULL;
+
+void SuspendibleThreadSet_init() {
+  assert(_synchronize_wakeup == NULL, "STS already initialized");
+  _synchronize_wakeup = new Semaphore();
+}
+
+bool SuspendibleThreadSet::is_synchronized() {
+  assert_lock_strong(STS_lock);
+  assert(_nthreads_stopped <= _nthreads, "invariant");
+  return _nthreads_stopped == _nthreads;
+}
+
+void SuspendibleThreadSet::join() {
+  assert(!Thread::current()->is_suspendible_thread(), "Thread already joined");
+  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
+  while (_suspend_all) {
+    ml.wait(Mutex::_no_safepoint_check_flag);
+  }
+  _nthreads++;
+  DEBUG_ONLY(Thread::current()->set_suspendible_thread();)
+}
+
+void SuspendibleThreadSet::leave() {
+  assert(Thread::current()->is_suspendible_thread(), "Thread not joined");
+  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
+  assert(_nthreads > 0, "Invalid");
+  DEBUG_ONLY(Thread::current()->clear_suspendible_thread();)
+  _nthreads--;
+  if (_suspend_all && is_synchronized()) {
+    // This leave completes a request, so inform the requestor.
+    _synchronize_wakeup->signal();
+  }
+}
+
+void SuspendibleThreadSet::yield() {
+  assert(Thread::current()->is_suspendible_thread(), "Must have joined");
+  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
+  if (_suspend_all) {
+    _nthreads_stopped++;
+    if (is_synchronized()) {
+      if (ConcGCYieldTimeout > 0) {
+        double now = os::elapsedTime();
+        guarantee((now - _suspend_all_start) * 1000.0 < (double)ConcGCYieldTimeout, "Long delay");
+      }
+      // This yield completes the request, so inform the requestor.
+      _synchronize_wakeup->signal();
+    }
+    while (_suspend_all) {
+      ml.wait(Mutex::_no_safepoint_check_flag);
+    }
+    assert(_nthreads_stopped > 0, "Invalid");
+    _nthreads_stopped--;
+  }
+}
+
+void SuspendibleThreadSet::synchronize() {
+  assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
+  if (ConcGCYieldTimeout > 0) {
+    _suspend_all_start = os::elapsedTime();
+  }
+  {
+    MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
+    assert(!_suspend_all, "Only one at a time");
+    _suspend_all = true;
+    if (is_synchronized()) {
+      return;
+    }
+  } // Release lock before semaphore wait.
+
+  // Semaphore initial count is zero.  To reach here, there must be at
+  // least one not yielded thread in the set, e.g. is_synchronized()
+  // was false before the lock was released.  A thread in the set will
+  // signal the semaphore iff it is the last to yield or leave while
+  // there is an active suspend request.  So there will be exactly one
+  // signal, which will increment the semaphore count to one, which
+  // will then be consumed by this wait, returning it to zero.  No
+  // thread can exit yield or enter the set until desynchronize is
+  // called, so there are no further opportunities for the semaphore
+  // being signaled until we get back here again for some later
+  // synchronize call.  Hence, there is no need to re-check for
+  // is_synchronized after the wait; it will always be true there.
+  _synchronize_wakeup->wait();
+
+#ifdef ASSERT
+  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
+  assert(_suspend_all, "STS not synchronizing");
+  assert(is_synchronized(), "STS not synchronized");
+#endif
+}
+
+void SuspendibleThreadSet::desynchronize() {
+  assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
+  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
+  assert(_suspend_all, "STS not synchronizing");
+  assert(is_synchronized(), "STS not synchronized");
+  _suspend_all = false;
+  ml.notify_all();
+}

--- /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