SpinLock.h

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/*
 * Copyright (c) 2018 pongasoft
 *
 * Licensed under the Apache License, Version 2.0 or the MIT license,
 * at your option. You may not use this file except in compliance with
 * one of these licenses. You may obtain copies of the licenses at:
 *
 * https://www.apache.org/licenses/LICENSE-2.0
 * https://opensource.org/licenses/MIT
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 * 
 * @author Yan Pujante
 */
 
#pragma once
 
#include <atomic>

class SpinLock
{
public:
 
  class Lock
  {
  public:
    ~Lock()
    {
      if(fSpinLock != nullptr)
        fSpinLock->unlock();
    }
 
    Lock(Lock &&iLock) noexcept : fSpinLock{iLock.fSpinLock}
    {
      iLock.fSpinLock = nullptr;
    }
 
    Lock(Lock const &) = delete;
    Lock& operator=(Lock const &) = delete;
 
  private:
    friend class SpinLock;
 
    explicit Lock(SpinLock *iSpinLock) : fSpinLock{iSpinLock}
    {
    }
 
 
    SpinLock *fSpinLock;
  };
 
  SpinLock() = default;

  Lock acquire()
  {
    while(fFlag.test_and_set(std::memory_order_acquire))
    {
      // nothing to do => spin
    }
 
    return Lock(this);
  }
 
 
  SpinLock(SpinLock const &) = delete;
 
  SpinLock &operator=(SpinLock const &) = delete;
 
private:
  friend class Lock;
 
  void unlock()
  {
    fFlag.clear(std::memory_order_release);
  }
 
  std::atomic_flag fFlag;
};