等待另一个线程

时间：2012-08-16 15:31:16

标签： c# multithreading synchronization

所以我有这个程序试图在两个不同的线程thread1和thread2之间建立通信。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace Project1
{
    class Class1
    {
        public static void thread1() 
        {
            Console.WriteLine("1");
            Console.WriteLine("t2 has printed 1, so we now print 2");
            Console.WriteLine("t2 has printed 2, so we now print 3");
        }

        public static void thread2()
        {
            Console.WriteLine("t1 has printed 1, so we now print 1");
            Console.WriteLine("t1 has printed 2, so we now print 2");
            Console.WriteLine("t1 has printed 3, so we now print 3");
        }

        public static void Main() {

            Thread t1 = new Thread(new ThreadStart(() => thread1()));
            Thread t2 = new Thread(new ThreadStart(() => thread2()));
            t1.Start();
            t2.Start();
            t2.Join();
            t1.Join();

        }

    }
}

但是，我希望它出现在这一行：

Console.WriteLine("1");

...首先执行，而thread2只是等待执行此行。然后才会打印出来：

Console.WriteLine("t1 has printed 1, so we now print 1");

打印完这一行后，只有这一行：

Console.WriteLine("t2 has printed 1, so we now print 2");

...打印，依此类推。所以我想更改代码，以便线程相互通信，以便按以下顺序打印行：

            Console.WriteLine("1"); // from t1
            Console.WriteLine("t1 has printed 1, so we now print 1"); // from t2
            Console.WriteLine("t2 has printed 1, so we now print 2"); // from t1
            Console.WriteLine("t1 has printed 2, so we now print 2"); // from t2
            Console.WriteLine("t2 has printed 2, so we now print 3"); // from t1
            Console.WriteLine("t1 has printed 3, so we now print 3"); // from t2

我理解锁的作用，但它仅适用于两个不同的线程在同一个函数上运行的情况。但是，这里两个函数不同，因此我不能在这里使用锁。

有什么想法吗？

4 个答案:

答案 0 :(得分：9)

您似乎需要Monitor.Wait和Monitor.Pulse。线程上有一个free eBook（可能有很多，但这个对我有帮助）。

您可以使用静态对象锁定，然后让您的线程调用Monitor.Pulse来表示他们“轮到他们完成”并Monitor.Wait“等待他们的下一轮”。以下是使用基本代码的示例实现：

public class Class1
{
     // Use this to syncrhonize threads
    private static object SyncRoot = new object();
     // First "turn" goes to thread 1
    private static int threadInControl = 1;

    public static void thread1()
    {
        lock(SyncRoot) // Request exclusive access to SyncRoot
        {
            Console.WriteLine("1");
            GiveTurnTo(2); // Let thread 2 have a turn
            WaitTurn(1);   // Wait for turn to be given to thread 1
            Console.WriteLine("t2 has printed 1, so we now print 2");
            GiveTurnTo(2); // Let thread 2 have a turn
            WaitTurn(1);   // Wait for turn to be given to thread 1
            Console.WriteLine("t2 has printed 2, so we now print 3");
            GiveTurnTo(2); // Let thread 2 have a turn
        }
    }

    public static void thread2()
    {
        lock(SyncRoot) // Request exclusive access to SyncRoot
        {
            WaitTurn(2);   // Wait for turn to be given to thread 2
            Console.WriteLine("t1 has printed 1, so we now print 1");
            GiveTurnTo(1); // Let thread 1 have a turn
            WaitTurn(2);   // Wait for turn to be given to thread 2
            Console.WriteLine("t1 has printed 2, so we now print 2");
            GiveTurnTo(1); // Let thread 1 have a turn
            WaitTurn(2);   // Wait for turn to be given to thread 2
            Console.WriteLine("t1 has printed 3, so we now print 3");
            GiveTurnTo(1); // Let thread 1 have a turn
        }
    }

    // Wait for turn to use SyncRoot object
    public static void WaitTurn(int threadNum)
    {
        // While( not this threads turn )
        while (threadInControl != threadNum)
        {
            // "Let go" of lock on SyncRoot and wait utill 
            // someone finishes their turn with it
            Monitor.Wait(SyncRoot);
        }
    }

    // Pass turn over to other thread
    public static void GiveTurnTo(int nextThreadNum)
    {
        threadInControl = nextThreadNum;
        // Notify waiting threads that it's someone else's turn
        Monitor.Pulse(SyncRoot);
    }

    public static void  void Main()
    {
        Thread t1 = new Thread(new ThreadStart(() => Class1.thread1()));
        Thread t2 = new Thread(new ThreadStart(() => Class1.thread2()));
        t1.Start();
        t2.Start();
        t2.Join();
        t1.Join();
    }
}

至于使用lock keyword，它不限于同一功能内的同步。锁“保证”对单个线程的资源（对象）的独占访问（通过独占，我的意思是一次只有一个线程可以获得对该资源的锁定，锁定不会阻止其他线程简单地访问对象本身）

为了简化它，lock(someObject)就像一个线程使用someOject，然后等到它前面的所有其他线程完成转弯才继续。线程在离开lock语句的范围时结束其“转向”（除非您添加Monitor.Pulse或Monitor.Wait之类的内容。）

答案 1 :(得分：3)

使用ManualResetEvent。在线程2中等待它并在Console.WriteLn（）之后在thread1中设置它 http://msdn.microsoft.com/en-us/library/system.threading.manualresetevent.aspx

答案 2 :(得分：2)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace Project1
{
    class Class1
    {
        private static ManualResetEvent mre1 = new ManualResetEvent(false);
        private static ManualResetEvent mre2 = new ManualResetEvent(false);

        public static void thread1() 
        {
            Console.WriteLine("1");
            mre2.Set();
            mre1.WaitOne();
            Console.WriteLine("t2 has printed 1, so we now print 2");
            mre2.Set();
            mre1.WaitOne();
            Console.WriteLine("t2 has printed 2, so we now print 3");
        }

        public static void thread2()
        {
            mre2.WaitOne();
            Console.WriteLine("t1 has printed 1, so we now print 1");
            mre1.Set();
            mre2.WaitOne();
            Console.WriteLine("t1 has printed 2, so we now print 2");
            mre1.Set();
            mre2.WaitOne();
            Console.WriteLine("t1 has printed 3, so we now print 3");
        }

        public static void Main() {

            Thread t1 = new Thread(new ThreadStart(() => thread1()));
            Thread t2 = new Thread(new ThreadStart(() => thread2()));

            t1.Start();
            t2.Start();

            while (true) {
                Thread.Sleep(1);
            }

        }

    }
}

谢谢你们。我想我现在有了解决方案！

答案 3 :(得分：1)

来自Joe Albahari先生的高级线程教程中包含的“等待和脉冲信号”部分的Two-Way Signaling and Races部分中给出的示例：

static readonly object locker = new object();
private static bool ready, go;

public static void Thread1()
{
  IEnumerable<Action> actions = new List<Action>()
  {
   () => Console.WriteLine("1"),
   () => Console.WriteLine("t2 has printed 1, so we now print 2"),
   () => Console.WriteLine("t2 has printed 2, so we now print 3")
  };

  foreach (var action in actions)
  {
    lock (locker)
    {
      while (!ready) Monitor.Wait(locker);
      ready = false;
      go = true;
      Monitor.PulseAll(locker);
      action();
    } 
  }
}

public static void Thread2()
{
  IEnumerable<Action> actions = new List<Action>()
  {
   () => Console.WriteLine("t1 has printed 1, so we now print 1"),
   () => Console.WriteLine("t1 has printed 2, so we now print 2"),
   () => Console.WriteLine("t1 has printed 3, so we now print 3")
  };

  foreach (var action in actions)
  {
    lock (locker)
    {
      ready = true;
      Monitor.PulseAll(locker);
      while (!go) Monitor.Wait(locker);
      go = false;
      action();
    }
  }
}

private static void Main(string[] args)
{
  Thread t1 = new Thread(new ThreadStart(() => Thread1()));
  Thread t2 = new Thread(new ThreadStart(() => Thread2()));
  t1.Start();
  t2.Start();
  t2.Join();
  t1.Join();
}
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