--- /dev/null	2017-11-09 09:38:01.297999907 +0100
+++ new/src/hotspot/share/jfr/recorder/service/jfrPostBox.cpp	2018-04-09 15:11:51.770560549 +0200
@@ -0,0 +1,173 @@
+/*
+ * Copyright (c) 2013, 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.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "jfr/recorder/service/jfrPostBox.hpp"
+#include "jfr/utilities/jfrTryLock.hpp"
+#include "runtime/atomic.hpp"
+#include "runtime/orderAccess.inline.hpp"
+#include "runtime/thread.inline.hpp"
+
+#define MSG_IS_SYNCHRONOUS ( (MSGBIT(MSG_ROTATE)) |          \
+                             (MSGBIT(MSG_STOP))   |          \
+                             (MSGBIT(MSG_START))  |          \
+                             (MSGBIT(MSG_CLONE_IN_MEMORY)) | \
+                             (MSGBIT(MSG_VM_ERROR))          \
+                           )
+
+static JfrPostBox* _instance = NULL;
+
+JfrPostBox& JfrPostBox::instance() {
+  return *_instance;
+}
+
+JfrPostBox* JfrPostBox::create() {
+  assert(_instance == NULL, "invariant");
+  _instance = new JfrPostBox();
+  return _instance;
+}
+
+void JfrPostBox::destroy() {
+  assert(_instance != NULL, "invariant");
+  delete _instance;
+  _instance = NULL;
+}
+
+JfrPostBox::JfrPostBox() :
+  _msg_read_serial(0),
+  _msg_handled_serial(0),
+  _messages(0),
+  _has_waiters(false) {}
+
+static bool is_thread_lock_aversive() {
+  Thread* const thread = Thread::current();
+  return (thread->is_Java_thread() && ((JavaThread*)thread)->thread_state() != _thread_in_vm) || thread->is_VM_thread();
+}
+
+static bool is_synchronous(int messages) {
+  return ((messages & MSG_IS_SYNCHRONOUS) != 0);
+}
+
+void JfrPostBox::post(JFR_Msg msg) {
+  const int the_message = MSGBIT(msg);
+  if (is_thread_lock_aversive()) {
+    deposit(the_message);
+    return;
+  }
+  if (!is_synchronous(the_message)) {
+    asynchronous_post(the_message);
+    return;
+  }
+  synchronous_post(the_message);
+}
+
+void JfrPostBox::deposit(int new_messages) {
+  while (true) {
+    const int current_msgs = OrderAccess::load_acquire(&_messages);
+    // OR the new message
+    const int exchange_value = current_msgs | new_messages;
+    const int result = Atomic::cmpxchg(exchange_value, &_messages, current_msgs);
+    if (result == current_msgs) {
+      return;
+    }
+    /* Some other thread just set exactly what this thread wanted */
+    if ((result & new_messages) == new_messages) {
+      return;
+    }
+  }
+}
+
+void JfrPostBox::asynchronous_post(int msg) {
+  assert(!is_synchronous(msg), "invariant");
+  deposit(msg);
+  JfrMonitorTryLock try_msg_lock(JfrMsg_lock);
+  if (try_msg_lock.acquired()) {
+    JfrMsg_lock->notify_all();
+  }
+}
+
+void JfrPostBox::synchronous_post(int msg) {
+  assert(is_synchronous(msg), "invariant");
+  assert(!JfrMsg_lock->owned_by_self(), "should not hold JfrMsg_lock here!");
+  MutexLockerEx msg_lock(JfrMsg_lock);
+  deposit(msg);
+  // serial_id is used to check when what we send in has been processed.
+  // _msg_read_serial is read under JfrMsg_lock protection.
+  const uintptr_t serial_id = OrderAccess::load_acquire(&_msg_read_serial) + 1;
+  JfrMsg_lock->notify_all();
+  while (!is_message_processed(serial_id)) {
+    JfrMsg_lock->wait();
+  }
+}
+
+/*
+ * Check if a synchronous message has been processed.
+ * We avoid racing on _msg_handled_serial by ensuring
+ * that we are holding the JfrMsg_lock when checking
+ * completion status.
+ */
+bool JfrPostBox::is_message_processed(uintptr_t serial_id) const {
+  assert(JfrMsg_lock->owned_by_self(), "_msg_handled_serial must be read under JfrMsg_lock protection");
+  return serial_id <= OrderAccess::load_acquire(&_msg_handled_serial);
+}
+
+bool JfrPostBox::is_empty() const {
+  assert(JfrMsg_lock->owned_by_self(), "not holding JfrMsg_lock!");
+  return OrderAccess::load_acquire(&_messages) == 0;
+}
+
+int JfrPostBox::collect() {
+  // get pending and reset to 0
+  const int messages = Atomic::xchg(0, &_messages);
+  if (check_waiters(messages)) {
+    _has_waiters = true;
+    assert(JfrMsg_lock->owned_by_self(), "incrementing _msg_read_serial is protected by JfrMsg_lock");
+    // Update made visible on release of JfrMsg_lock via fence instruction in Monitor::IUnlock.
+    ++_msg_read_serial;
+  }
+  return messages;
+}
+
+bool JfrPostBox::check_waiters(int messages) const {
+  assert(JfrMsg_lock->owned_by_self(), "not holding JfrMsg_lock!");
+  assert(!_has_waiters, "invariant");
+  return is_synchronous(messages);
+}
+
+void JfrPostBox::notify_waiters() {
+  if (!_has_waiters) {
+    return;
+  }
+  _has_waiters = false;
+  assert(JfrMsg_lock->owned_by_self(), "incrementing _msg_handled_serial is protected by JfrMsg_lock.");
+  // Update made visible on release of JfrMsg_lock via fence instruction in Monitor::IUnlock.
+  ++_msg_handled_serial;
+  JfrMsg_lock->notify();
+}
+
+// safeguard to ensure no threads are left waiting
+void JfrPostBox::notify_collection_stop() {
+  MutexLockerEx msg_lock(JfrMsg_lock);
+  JfrMsg_lock->notify_all();
+}