/*

 * Copyright (c) 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.

 *

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 */

#ifndef SHARE_UTILITIES_SPINYIELD_HPP

#define SHARE_UTILITIES_SPINYIELD_HPP

#include "memory/allocation.hpp"

#include "utilities/globalDefinitions.hpp"

#include "utilities/ticks.hpp"

class outputStream;

extern "C" int SpinPause();

class SpinYield : public StackObj {

  Tickspan _sleep_time;

  uint _spins;

  uint _yields;

  uint _spin_limit;

  uint _yield_limit;

  void yield_or_sleep();

public:

  static const uint default_spin_limit = 4096;

  static const uint default_yield_limit = 64;

  // spin_limit is ignored (treated as zero) when !os::is_MP().

  explicit SpinYield(uint spin_limit = default_spin_limit,

                     uint yield_limit = default_yield_limit);

  // Perform next round of delay.

  void wait() {

    // Simple policy: return immediately (spinning) configured number

    // of times, then switch to yield/sleep.  Future work might

    // provide other policies, such as (1) always spin if system is

    // not saturated, or (2) sleeping if yielding is ineffective.

    if (_spins < _spin_limit) {

      ++_spins;

      SpinPause();

    } else {

      yield_or_sleep();

    }

  }

  // Write information about the wait duration to s.

  void report(outputStream* s) const;

};

#endif // SHARE_UTILITIES_SPINYIELD_HPP