--- old/src/share/vm/runtime/thread.cpp	Tue Feb 17 13:56:35 2015
+++ new/src/share/vm/runtime/thread.cpp	Tue Feb 17 13:56:34 2015
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 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
@@ -1196,8 +1196,16 @@
 }
 
 int WatcherThread::sleep() const {
+  // The WatcherThread does not honor the safepoint protocol for
+  // PeriodicTask_lock in order to provide more consistent task
+  // execution timing.
   MutexLockerEx ml(PeriodicTask_lock, Mutex::_no_safepoint_check_flag);
 
+  if (_should_terminate) {
+    // check for termination before we do any housekeeping or wait
+    return 0;  // we did not sleep.
+  }
+
   // remaining will be zero if there are no tasks,
   // causing the WatcherThread to sleep until a task is
   // enrolled
@@ -1210,8 +1218,9 @@
 
   jlong time_before_loop = os::javaTimeNanos();
 
-  for (;;) {
-    bool timedout = PeriodicTask_lock->wait(Mutex::_no_safepoint_check_flag, remaining);
+  while (true) {
+    bool timedout = PeriodicTask_lock->wait(Mutex::_no_safepoint_check_flag,
+                                            remaining);
     jlong now = os::javaTimeNanos();
 
     if (remaining == 0) {
@@ -1252,7 +1261,7 @@
   this->initialize_thread_local_storage();
   this->set_native_thread_name(this->name());
   this->set_active_handles(JNIHandleBlock::allocate_block());
-  while (!_should_terminate) {
+  while (true) {
     assert(watcher_thread() == Thread::current(), "thread consistency check");
     assert(watcher_thread() == this, "thread consistency check");
 
@@ -1288,6 +1297,11 @@
       }
     }
 
+    if (_should_terminate) {
+      // check for termination before posting the next tick
+      break;
+    }
+
     PeriodicTask::real_time_tick(time_waited);
   }
 
@@ -1318,27 +1332,20 @@
 }
 
 void WatcherThread::stop() {
-  // Get the PeriodicTask_lock if we can. If we cannot, then the
-  // WatcherThread is using it and we don't want to block on that lock
-  // here because that might cause a safepoint deadlock depending on
-  // what the current WatcherThread tasks are doing.
-  bool have_lock = PeriodicTask_lock->try_lock();
+  {
+    // Follow normal safepoint aware lock enter protocol since the
+    // WatcherThread is stopped by another JavaThread.
+    MutexLocker ml(PeriodicTask_lock);
+    _should_terminate = true;
+    OrderAccess::fence();  // ensure WatcherThread sees update in main loop
 
-  _should_terminate = true;
-  OrderAccess::fence();  // ensure WatcherThread sees update in main loop
-
-  if (have_lock) {
     WatcherThread* watcher = watcher_thread();
     if (watcher != NULL) {
-      // If we managed to get the lock, then we should unpark the
-      // WatcherThread so that it can see we want it to stop.
+      // unpark the WatcherThread so it can see that it should terminate
       watcher->unpark();
     }
-
-    PeriodicTask_lock->unlock();
   }
 
-  // it is ok to take late safepoints here, if needed
   MutexLocker mu(Terminator_lock);
 
   while (watcher_thread() != NULL) {
@@ -1358,9 +1365,7 @@
 }
 
 void WatcherThread::unpark() {
-  MutexLockerEx ml(PeriodicTask_lock->owned_by_self()
-                   ? NULL
-                   : PeriodicTask_lock, Mutex::_no_safepoint_check_flag);
+  assert(PeriodicTask_lock->owned_by_self(), "PeriodicTask_lock required");
   PeriodicTask_lock->notify();
 }
 
@@ -3557,8 +3562,8 @@
   }
 
   {
-    MutexLockerEx ml(PeriodicTask_lock, Mutex::_no_safepoint_check_flag);
-    // Make sure the watcher thread can be started by WatcherThread::start()
+    MutexLocker ml(PeriodicTask_lock);
+    // Make sure the WatcherThread can be started by WatcherThread::start()
     // or by dynamic enrollment.
     WatcherThread::make_startable();
     // Start up the WatcherThread if there are any periodic tasks