C＃线程问题与的AutoResetEvent [英] C# Threading issue with AutoResetEvent

问题描述

如何正确同步呢？目前，它是可能的的SetData 终止后， e.WaitOne（）已完成所谓的 D 可能已被设置为另一个值。我试图插入锁，但它导致陷入僵持。

How to properly synchronize this? At the moment it is possible that SetData is called after e.WaitOne() has completed so d could be already set to another value. I tried to insert locks but it resulted into a deadlock.

AutoResetEvent e = new AutoResetEvent(false);

public SetData(MyData d)
{
   this.d=d;
   e.Set();    // notify that new data is available
}

// This runs in separate thread and waits for d to be set to a new value
void Runner() 
{    
   while (true)
   {
      e.WaitOne();  // waits for new data to process
      DoLongOperationWith_d(d);
   }
}

请问最好的解决办法是引入一个新的布尔变量即在的SetData 设置为true，并在 DoLongOperationWith_d dataAlreadyBeenSetAndWaitingToBeProcessed

Will the best solution be to introduce a new boolean variable dataAlreadyBeenSetAndWaitingToBeProcessed that is set in SetData to true and at the end of DoLongOperationWith_d it could be set to true, so if SetData is called with this variable set to true it could just return?

推荐答案

这是未经测试，而是一种优雅的方式与基于.NET元要做到这一点：

This is untested, but is an elegant way to do this with the .net based primitives:

class Processor<T> {
    Action<T> action;
    Queue<T> queue = new Queue<T>();

    public Processor(Action<T> action) {
        this.action = action;
        new Thread(new ThreadStart(ThreadProc)).Start();
    }

    public void Queue(T data) {
        lock (queue) {
            queue.Enqueue(data);
            Monitor.Pulse(queue); 
        }            
    }

    void ThreadProc() {
        Monitor.Enter(queue);
        Queue<T> copy;

        while (true) {                 
            if (queue.Count == 0) {
                Monitor.Wait(queue);
            }

            copy = new Queue<T>(queue);
            queue.Clear();
            Monitor.Exit(queue);

            foreach (var item in copy) {
                action(item); 
            }

            Monitor.Enter(queue); 
        }
    }
}

程序范例：

Example program:

class Program {

    static void Main(string[] args) {

        Processor<int> p = new Processor<int>((data) => { Console.WriteLine(data);  });
        p.Queue(1);
        p.Queue(2); 

        Console.Read();

        p.Queue(3);
    }
}

这是一个非队列版本，队列版本可优选：

This is a non-queue version, a queue version may be preferred:

object sync = new object(); 
AutoResetEvent e = new AutoResetEvent(false);
bool pending = false; 

public SetData(MyData d)
{
   lock(sync) 
   {
      if (pending) throw(new CanNotSetDataException()); 

      this.d=d;
      pending = true;
   }

   e.Set();    // notify that new data is available
}

void Runner() // this runs in separate thread and waits for d to be set to a new value
{

     while (true)
     {

             e.WaitOne();  // waits for new data to process
             DoLongOperationWith_d(d);
             lock(sync) 
             {
                pending = false; 
             }
     }
}

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