fastlock.h

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/*
 * Copyright (c) 2005, Eric Crahen
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is furnished
 * to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 */

#ifndef __ZTFASTLOCK_H__
#define __ZTFASTLOCK_H__

#include "zthread/Exceptions.h"
#include "zthread/NonCopyable.h"
#include "../ThreadOps.h"
#include <windows.h>
#include <assert.h>

namespace ZThread {

  /**
   * @class FastLock
   *
   * @author Eric Crahen <http://www.code-foo.com>
   * @date <2003-07-16T23:32:44-0400>
   * @version 2.2.11
   *
   * This FastLock implementation is based on a Win32 Mutex
   * object. This will perform better under high contention, 
   * but will not be as fast as the spin lock under reasonable
   * circumstances.
   */ 
  class FastLock : private NonCopyable {

    HANDLE _hMutex;
#ifndef NDEBUG
    volatile bool _locked;
#endif

  public:
  
    /**
     * Create a new FastLock
     */
    FastLock() { 

#ifndef NDEBUG
      _locked = false;
#endif

      _hMutex = ::CreateMutex(0, 0, 0);
      assert(_hMutex != NULL);
      if(_hMutex == NULL)
        throw Initialization_Exception();

    }

  
    ~FastLock() {
      ::CloseHandle(_hMutex);
    }
  
  void acquire() {

    if(::WaitForSingleObject(_hMutex, INFINITE) != WAIT_OBJECT_0) {
      assert(0);
      throw Synchronization_Exception();
    }

#ifndef NDEBUG

    // Simulate deadlock to provide consistent behavior. This
    // will help avoid errors when porting. Avoiding situations
    // where a FastMutex mistakenly behaves as a recursive lock.

    while(_locked)
      ThreadOps::yield();

    _locked = true;

#endif

  }

  void release() {

#ifndef NDEBUG
    _locked = false;
#endif

    if(::ReleaseMutex(_hMutex) == 0) {
      assert(0);
      throw Synchronization_Exception();
    }

  }


  bool tryAcquire(unsigned long timeout = 0) {

    switch(::WaitForSingleObject(_hMutex, timeout)) {
      case WAIT_OBJECT_0:
      
#ifndef NDEBUG

        // Simulate deadlock to provide consistent behavior. This
        // will help avoid errors when porting. Avoiding situations
        // where a FastMutex mistakenly behaves as a recursive lock.

        while(_locked)
          ThreadOps::yield();
      
        _locked = true;

#endif

        return true;
      case WAIT_TIMEOUT:
        return false;
      default:
        break;
    }

    assert(0);
    throw Synchronization_Exception();

  }

 };

} // namespace ZThread

#endif