c# - 为什么这个例子中的队列锁是必要的

Question

我有下面显示的示例。我不知道为什么队列SyncRoot也有锁定，而这两种连贯算法都使用同一个对象完全锁定。

据说队列锁是必须的。

public class CrudeThreadPool
{
    static readonly int MaxWorkThreads = 4;
    static readonly int WaitTimeout = 2000;

    public delegate void WorkDelegate();

    public CrudeThreadPool() {
        stop = false;
        workLock = new Object();
        workQueue = new Queue();
        threads = new Thread[ MaxWorkThreads ];

        for( int i = 0; i < MaxWorkThreads; ++i ) {
            threads[i] =
                new Thread( new ThreadStart(this.ThreadFunc) );
            threads[i].Start();
        }
    }

    private void ThreadFunc() {
        lock( workLock ) {
            do {
                if( !stop ) {
                    WorkDelegate workItem = null;
                    if( Monitor.Wait(workLock, WaitTimeout) ) {
        
                        lock( workQueue.SyncRoot ) {
                            workItem =
                                (WorkDelegate) workQueue.Dequeue();
                        }
                        workItem();
                    }
                }
            } while( !stop );
        }
    }

    public void SubmitWorkItem( WorkDelegate item ) {
        lock( workLock ) {
            lock( workQueue.SyncRoot ) {
                workQueue.Enqueue( item );
            }

            Monitor.Pulse( workLock );
        }
    }

    public void Shutdown() {
        stop = true;
    }

    private Queue         workQueue;
    private Object        workLock;
    private Thread[]      threads;
    private volatile bool stop;
}

锁定队列的原因是什么SyncRoot，即lock(workQueue.SyncRoot )？

Answer 1

内部锁实际上不是必需的，因为只要没有再次达到等待，锁就会被持有并阻塞所有生产者。因此这应该工作：

private void ThreadFunc() {
   do {
        if( !stop ) {
            WorkDelegate workItem = null;
            lock( workLock ) {
                if( Monitor.Wait(workLock, WaitTimeout) ) {
                    workItem = (WorkDelegate) workQueue.Dequeue();
                }
            }
            if (workItem != null) workItem();
        }
    } while( !stop );
}

public void SubmitWorkItem( WorkDelegate item ) 
{
    lock( workLock ) {
        workQueue.Enqueue( item );

        Monitor.Pulse( workLock );
    }
}

Joseph Albahari 的网站是线程场景的绝佳参考。虽然这是一个经典的生产者/消费者场景，但我建议您使用BlockingCollection。