win32多线程程序设计（四）--- 读写锁

原理： 读读相容，读写互斥，写写互斥。

 在第一读线程获取数据锁，在完成读的最后一个线程释放数据锁，由于获取和释放可能在不同线程，需要使用事件或信号量。

 

用delphi写了一个简单的读写锁 

 

 

 TReadWriteLock = class(TObject)

  private

    FReadCount: Integer;

    FReadCountLock: TCriticalSection;

    FDataLock: THandle;

  public

    constructor Create;

    destructor Destroy; override;

    function AcquireReadLock: Boolean;

    function ReleaseReadLock: Boolean;

    function AcquireWriteLock: Boolean;

    function ReleaseWriteLock: Boolean;

  end;

implementation

{ TReadWriteLock }

function TReadWriteLock.AcquireWriteLock: Boolean;

begin

  if WAIT_OBJECT_0 = WaitForSingleObject(FDataLock, INFINITE)  then  Result := True

  else Result := False;

end;

constructor TReadWriteLock.Create;

begin

  FReadCountLock := TCriticalSection.Create;

  FDataLock := CreateSemaphore(nil, 1, 1, '');

end;

destructor TReadWriteLock.Destroy;

begin

  FreeAndNil(FReadCountLock);

  CloseHandle(FDataLock);

  inherited;

end;

function TReadWriteLock.GetReadCount: Integer;

begin

  Result := FReadCount;

end;

function TReadWriteLock.ReleaseReadLock: Boolean;

begin

  Result := False;

  FReadCountLock.Acquire;

  try

    Dec(FReadCount);

    if FReadCount = 0 then Result := ReleaseSemaphore(FDataLock, 1, nil);

  finally

    FReadCountLock.Release;

  end;

end;

function TReadWriteLock.AcquireReadLock: Boolean;

begin

  Result := False;

  FReadCountLock.Acquire;

  try

    if FReadCount = 0 then

      if WAIT_OBJECT_0 = WaitForSingleObject(FDataLock, INFINITE)  then  Result := True;

    Inc(FReadCount);  

  finally

    FReadCountLock.Release;

  end;

end;