如何等待方法在另一个线程上完成？

Question

I am new to multi-thread programming in C#. My problem is that I don't know how to wait for a method that is being run on another thread to finish, before it can continue to the next line. For example, something like this

public class A
{    
    int i;

    public A()
    {
        i = 0;
    }

    protected void RunLoop()
    {
        while(i < 100)
        {
            i++;
        }
    }

    public void Start()
    {
        TimerResolution.TimeBeginPeriod(1);
        runThread = new Thread(new ThreadStart(RunLoop));
        running = true;
        runThread.Start();
    }
}

public class B
{
    A classAInstance = new A();
    A.Start();
    Console.Writeline(i);
}

Right now, it prints 0 on the console, which is not what I want (ie i = 100). What is the best way to do this? BTW, I don't have access to the runThread that is created in class A

Thanks.

EDIT:

It was a bit difficult to solve this problem without modifying a lot codes. Therefore, we ended up with adding a condition in the public void Start() with which it can decide whether to run the RunLoop in a separate thread or not. The condition was defined using an Enum field.

public void Start()
{
    TimerResolution.TimeBeginPeriod(1);
    running = true;
    if (runningMode == RunningMode.Asynchronous)
    {
        runThread = new Thread(new ThreadStart(RunLoop));
        runThread.Start();
    }
    else
    {
        RunLoop();
    }
}

And

public enum RunningMode { Asynchronous, Synchronous };

Thanks everyone for help.

Answer 1

The preferred method is to use the Task Parallel Library (TPL) and use Task with await .

If you must use Threads, then use a ManualResetEvent or ManualResetEventSlim to signal the end of a method.

void Main()
{
    var a = new A();
    a.Start();
    a.FinishedEvent.WaitOne();
    Console.WriteLine(a.Index);
}

// Define other methods and classes here
public class A
{
    ManualResetEvent mre = new ManualResetEvent(false);
    int i;

    public EventWaitHandle FinishedEvent
    {
        get { return mre; }
    }

    public int Index
    {
        get { return i; }
    }

    public A()
    {
        i = 0;
    }

    protected void RunLoop()
    {
        while (i < 1000)
        {
            i++;
        }
        mre.Set();
    }

    public void Start()
    {
        var runThread = new Thread(new ThreadStart(RunLoop));
        runThread.Start();
    }
}

Answer 2

Your life would be so much better with tasks.

Your code could be this simple:

var task = Task.Factory.StartNew(() =>
{
    var i = 0;
    while (i < 100)
    {
        i++;
    }
    return i;
});

Console.WriteLine(task.Result);

Answer 3

I like use Monitor.Wait() and Monitor.Pulse() in conjunction with "lock" operator. It works, but you must be careful, when you use this technique. I'm added some changes to your code to demonstrate it. Code below are prints i== 100, as you want.

public class A
{
    int i;

    public object SyncObject
    {  get; private set; }

    public A()
    {
        SyncObject = new object();
        i = 0;
    }

    protected void RunLoop()
    {
        while (i < 100)
        {
            i++;
        }

        lock (SyncObject)
        {
            Monitor.Pulse(SyncObject);
        }
    }

    public void Start()
    {
        var runThread = new Thread(new ThreadStart(RunLoop));
        runThread.Start();
    }

    public void PrintI()
    {
        Console.WriteLine("I == " + i);
    }
}

public class B
{
    public static void Run()
    {
        A classAInstance = new A();
        lock (classAInstance.SyncObject)
        {
            classAInstance.Start();
            Monitor.Wait(classAInstance.SyncObject);
        }
        classAInstance.PrintI();
    }
}