/*
 *  ZThreads, a platform-independant, multithreading and 
 *  synchroniation library
 *
 *  Copyright (C) 2000-2002, Eric Crahen, See LGPL.TXT for details
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 *
 *  SUNY @ Buffalo, hereby disclaims all copyright interest in the
 *  ZThreads library written by Eric Crahen
 */

#ifndef __ZTFASTLOCK_H__
#define __ZTFASTLOCK_H__

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

namespace ZThread {


/**
 * @class FastLock
 *
 * @author Eric Crahen <crahen@cse.buffalo.edu>
 * @date <2002-05-24T11:36:51-0400>
 * @version 2.1.6
 *
 * This is the smallest and fastest synchronization object in the library.
 * It is an implementation of fast mutex, an all or nothing exclusive
 * lock. It should be used only where you need speed and are willing 
 * to sacrifice all the state & safety checking provided by the framework
 * for speed.
 *
 * The current Platform SDK defines:
 *
 *   LONG InterlockedExchange(LPLONG, LONG)
 *   LONG InterlockedCompareExchange(LPLONG, LONG, LONG, LONG) 
 *
 * If your compiler complains about LPLONG not being implicitly casted to
 * a PVOID, then you should get the SDK update from microsoft or use the 
 * WIN9X implementation of this class.
 *
 * ----
 * Because Windows 95 and earlier can run on processors prior to the 486, they
 * don't all support the CMPXCHG function, and so Windows 95 an earlier dont support
 * InterlockedCompareExchange. For this, you should use the win9x implementation
 * of this class
 */ 
class FastLock : private NonCopyable {

#pragma pack(push, 8)
  LONG volatile _lock;
#pragma pack(pop)
  
  public:
  
  /**
   * Create a new FastLock
   */
  inline FastLock() : _lock(0) { }

  
  /**
   * Destroy FastLock
   */
  inline ~FastLock() { assert(_lock == 0); }

  /**
   * Lock the fast Lock, no error check.
   * 
   * @exception None
   */ 
  inline void acquire() {

    while (::InterlockedCompareExchange(const_cast<LPLONG>(&_lock), 1, 0) != 0)
      ::Sleep(0);

  }

  
  /**
   * Release the fast Lock, no error check.
   * 
   * @exception None
   */ 
  inline void release() {

    ::InterlockedExchange(const_cast<LPLONG>(&_lock), (LONG)0);

  }
    
  /**
   * Try to acquire an exclusive lock. No safety or state checks are performed.
   * This function returns immediately regardless of the value of the timeout
   *
   * @param timeout Unused
   * @return bool
   * @exception Synchronization_Exception - not thrown
   */
 inline bool tryAcquire(unsigned long timeout=0) {
 
   return ::InterlockedCompareExchange(const_cast<LPLONG>(&_lock), 1, 0) == 0;

 }
  
}; /* FastLock */


};
#endif
