Question

我有一个方法，必须调用不超过一次，例如Dispose。现在，我意识到它是下一个：

private bool _isAlive = true;

public void Dispose()
{
    if (this._isAlive)
    {
        this._isAlive = false;
        //Do Something
    }
}

但它不是线程安全的，因为comprasion和设置标志_isAlive之间存在差距为false。因此，可能有多个线程执行//Do Something代码。

是否有线程安全的变体？

Answer 1

使用（根据评论更新）：

private long _isSomeMethodExecuted = 0;

public void Dispose()
{
 if ( Interlocked.Read ( ref this._isSomeMethodExecuted ) != 0 )
      return;

 if (Interlocked.Increment (ref this._isSomeMethodExecuted) == 1) //check if method is already executed
 {
        //Main code of method

 }
// leave the decrement out - this leads to 
// this method being callable exactly once as in the lifetime of the object
// Interlocked.Decrement (ref this._isSomeMethodExecuted);
}

参考http://msdn.microsoft.com/en-us/library/zs86dyzy.aspx

更新（根据@LukeH的评论）：

单个CompareExchange电话更简单/更好：

public void Dispose() 
{ 
if (Interlocked.CompareExchange(ref _isSomeMethodExecuted, 1, 0) == 0) 
{ /* main code of method */ } 
}

Answer 2

使用MethodImpAttribute是恕我直言的最简单方法。

  public void Dispose()
  {
      if (isAlive && ShouldDispose())
      {
          //Your code here
      }
  }

  [MethodImplAttribute(MethodImplOptions.Synchronized)]
  private bool ShouldDispose()
  {
       if (isAlive)
       {
            isAlive = false;
            return true;
       }
       return false;
  }

线程安全实现一次性方法

2 个答案: