diff -r c20cc2d3aa39 -r 64dba69fc528 src/hotspot/share/gc/shared/suspendibleThreadSet.cpp
--- /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();
+}