我正在尝试实现支持消费者超时的并发 生产环境 者 - 消费者集合(多个 生产环境 者和消费者) .

现在实际的集合非常复杂(不幸的是，在System.Collections.Concurrent中没有任何工作)，但我在这里有一个最小的示例来演示我的问题(看起来有点像 BlockingCollection ) .

public sealed class ProducerConsumerQueueDraft

{

private readonly Queue queue = new Queue();

private readonly object locker = new object();

public void Enqueue(T item)

{

lock (locker)

{

queue.Enqueue(item);

/* This "optimization" is broken, as Nicholas Butler points out.

if(queue.Count == 1) // Optimization

*/

Monitor.Pulse(locker); // Notify any waiting consumer threads.

}

}

public T Dequeue(T item)

{

lock (locker)

{

// Surprisingly, this needs to be a *while* and not an *if*

// which is the core of my problem.

while (queue.Count == 0)

Monitor.Wait(locker);

return queue.Dequeue();

}

}

// This isn't thread-safe, but is how I want TryDequeue to look.

public bool TryDequeueDesired(out T item, TimeSpan timeout)

{

lock (locker)

{

if (queue.Count == 0 && !Monitor.Wait(locker, timeout))

{

item = default(T);

return false;

}

// This is wrong! The queue may be empty even though we were pulsed!

item = queue.Dequeue();

return true;

}

}

// Has nasty timing-gymnastics I want to avoid.

public bool TryDequeueThatWorks(out T item, TimeSpan timeout)

{

lock (locker)

{

var watch = Stopwatch.StartNew();

while (queue.Count == 0)

{

var remaining = timeout - watch.Elapsed;

if (!Monitor.Wait(locker, remaining < TimeSpan.Zero ? TimeSpan.Zero : remaining))

{

item = default(T);

return false;

}

}

item = queue.Dequeue();

return true;

}

}

}

这个想法很简单：找到空队列的消费者等待发信号通知，并且生成者(注意：不是 PulseAll ，这将是低效的)他们通知他们等待的项目 .

当调用Pulse的线程释放锁定时，就绪队列中的下一个线程(不一定是脉冲线程)获取锁定 .

这意味着消费者线程C1可以被 生产环境 者线程唤醒以消耗一个项目，但是另一个消费者线程C2可以在C1有机会重新获取它之前获取锁定并消耗该项目，留下C1与给予控制时的空队列 .

这意味着如果队列确实非空，我必须在每个脉冲上防御性地检查消费者代码，如果不是这种情况，则返回并空手等待 .

我的主要问题是它效率低下 - 线程可能会被唤醒以进行工作，然后立即返回等待 . 这样做的一个相关结果是，当它应该是优雅的时候实现具有超时的 TryDequeue 是不必要的困难和低效的(参见 TryDequeueThatWorks )(参见 TryDequeueDesired ) .

How can I twist Monitor.Pulse to do what I want? Alternatively, is there another synchronization primitive that does? Is there a more efficient and/or elegant way to implement a TryDequeue timeout than what I have done?

仅供参考，这是一个测试，用于演示我所需解决方案的问题：

var queue = new ProducerConsumerQueueDraft();

for (int consumer = 0; consumer < 3; consumer++)

new Thread(() =>

{

while (true)

{

int item;

// This call should occasionally throw an exception.

// Switching to queue.TryDequeueThatWorks should make

// the problem go away.

if (queue.TryDequeueDesired(out item, TimeSpan.FromSeconds(1)))

{

// Do nothing.

}

}

}).Start();

Thread.Sleep(1000); // Let consumers get up and running

for (int itemIndex = 0; itemIndex < 50000000; itemIndex++)

{

queue.Enqueue(0);

}