线程安全替换代码? [英] Thread-safe replace for code?

问题描述

在开发过程中，我经常遇到下一个问题:如果某个方法已经由一个线程执行-方法一定不能由另一个线程执行.另一个线程什么也不做-从方法简单退出，因为我不能使用锁".通常，我会这样解决这个问题:

In process of developing I often face with the next problem: if some method is already executed by one thread - method is must not be executed by another thread. Another thread must do nothing - simple exit from method, beacuse of it I can't use "lock". Usually, I solve this problem like that:

private bool _isSomeMethodExecuted = false;

public void SomeMethod ()
{
 if (!this._isSomeMethodExecuted) //check if method is already executed
 {
        this._isSomeMethodExecuted = true;

        //Main code of method

        this._isSomeMethodExecuted = false;
 }
}

但是此代码不是线程安全的:如果一个线程执行条件语句，但是在set标志为true之前停止并且另一个线程可以执行条件-那么两个线程都在方法代码内部.

But this code is not thread-safe: if one thread execute condition statement but It be stopped before set flag in true and another thread can execute condition - then both threads are inside method code.

是否有任何线程安全的替代品?

Is there any thread-safe replace for it?

推荐答案

以下内容是线程安全的，并且即使该方法已在执行也不会阻塞-即使在同一线程上执行也很容易...这提供了保护在所有情况下都可以重新进入.

the following is thread-safe and does not block if the method is already executing - even if it is alreasy executing on the same thread... which provides protection from reentrancy for all scenarios.

private long _isSomeMethodExecuted = 0;

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

 }
Interlocked.Decrement (ref this._isSomeMethodExecuted);
}

有关参考，请参见 http://msdn.microsoft.com/zh-CN /library/zs86dyzy.aspx

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