Question

我需要实现从多个线程调用的简单函数。这个功能的逻辑很简单 - 想想赛马 - 一旦我们有一个胜利者，只有第一匹马才能获得金牌。

class ConditionalOrderGroup
{
    private volatile bool _locked = false;
    private List<ConditionalOrder> _ConditionalOrderList = null;        

public bool LockGroup(ConditionalOrder initiator)
{
   // this is finishline - we need to let only the first one proceed
    if (_locked)
        return false;
    else
    {
        _locked = true;
    }

    // this is what winner gets
    foreach (ConditionalOrder order in _ConditionalOrderList)
    {

      \\ cancel other orders
    }

    return true;
}
}

我对

不满意

if (_locked)
    return false;
else
{
    _locked = true;
}

如果两个订单可以通过，如果检查并继续其他，该怎么办？如何重写此代码不使用锁语句？

UPDATE 我的意思是我的目标不是使用像lock语句这样的阻塞方法。

Answer 1

您需要一个单独的私有对象并使用built-in locking：

private object padLock = new object();  // 1-to-1 with _ConditionalOrderList

if (Monitor.TryEnter(padLock))
{
   try 
   {
      // cancel other orders

      return true;
   } 
   finally 
   {
       Monitor.Exit(padLock);
   }
}
else
{
   return false;
}

Answer 2

使用Interlocked类以线程安全的方式更改变量的值。

Answer 3

扩展decyclone所说的关于互锁的内容，这正是你要做的：

const int LOCKED = 1;
const int UNLOCKED = 0;

volatile int lockState = UNLOCKED;

public bool Foo()
{
    try
    {
        //locking
        //compare exchange returns the value that was in lockState before the compareExchange operation, so from that you can determine if you grabbed the lock or not
        //if it was locked before, then you know the lock is not yours
        if (Interlocked.CompareExchange(ref lockState, UNLOCKED, LOCKED) == LOCKED)
            return false;

        //lock is yours, do whatever stuff you like here, including throw exceptions
    }
    finally
    {
        //unlocking
        //because this is in finally this lock will be released even if something goes wrong with your code
        Interlocked.Exchange(ref lockstate, UNLOCKED);
    }
}

如何实现简单的多线程函数

3 个答案: