/*

 * Copyright (c) 2013, 2019, 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.hpp"

#include "runtime/thread.inline.hpp"

#define MSG_IS_SYNCHRONOUS ( (MSGBIT(MSG_ROTATE)) |          \

                             (MSGBIT(MSG_STOP))   |          \

                             (MSGBIT(MSG_START))  |          \

                             (MSGBIT(MSG_CLONE_IN_MEMORY)) | \

                           )

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!");

  MonitorLocker 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;

  msg_lock.notify_all();

  while (!is_message_processed(serial_id)) {

    msg_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() {

  MutexLocker msg_lock(JfrMsg_lock);

  JfrMsg_lock->notify_all();

}