How wait all thread

Question

I have code, that create 5 threads. I need wait, until all threads finished their work, and after return value. How can I do this?

public static int num=-1;

public int GetValue()
{
    Thread t=null;
    for (int i = 0; i <=5; i++)
    {
        t = new Thread(() => PasswdThread(i));
        t.Start();  
    }

    //how wait all thread, and than return value?   
    return num;
}

public void PasswdThread(int i)
{
    Thread.Sleep(1000);
    Random r=new Random();
    int n=r.Next(10);
    if (n==5)
    {
        num=r.Next(1000);
    }
}

Of course this is not a real code. The actual code is much more complicated, so I simplified it.

P.S. Look carefully. I am not use Task, so I can't use method Wait() or WaitAll(). Also I can't use Join(), because Join wait one thread. If they start wait thread, which already finished they work, the will wait infinity.

http://msdn.microsoft.com/en-us/library/95hbf2ta.aspx or http://msdn.microsoft.com/en-us/library/dd537610.aspx — Karel Frajták, Jul 01 '13 at 13:42
What do you expect `num` to be? This won't scale to real code. — H H, Jul 01 '13 at 13:44
possible duplicate of [How to wait for thread to finish with .NET?](http://stackoverflow.com/questions/1584062/how-to-wait-for-thread-to-finish-with-net) — dirkk, Jul 01 '13 at 13:44
@jon-maximys go to visual studio, *Tools> Options> Text Editor> All Languages> Tabs* and select **Insert spaces** option — Sergey Berezovskiy, Jul 01 '13 at 13:53

score 3 · Answer 1 · edited Jul 01 '13 at 13:54

3

Make an array of thread like below and call WaitAll function

List<Thread> threads = new List<Thread>();
Thread thread = null;
 for (int i = 0; i <=5; i++)
 {
     t = new Thread(() => PasswdThread(i));
     t.Start();
     threads.add(t);
 }
Thread.WaitAll(thread);
 //how wait all thread, and than return value?  
 return num;

edited Jul 01 '13 at 13:54

gabba

2,815
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answered Jul 01 '13 at 13:47

rajansoft1

1,336
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Sorry @jon Maximys this function is not for threads, for threads you have to use thread pool try this http://msdn.microsoft.com/en-us/library/3dasc8as%28VS.80%29.aspx – rajansoft1 Jul 01 '13 at 14:19
or you can use Task Library to implement the same – rajansoft1 Jul 01 '13 at 14:20

score 2 · Accepted Answer · answered Jul 01 '13 at 13:43

2

create a ManualResetEvent handle for each your thread, and then call WaitHandle.WaitAll(handles) in your main thread.

static WaitHandle[] handles = new WaitHandle[5];

`

public void PasswdThread(int i)
{
handles[i] = new ManualResetEvent(false);

 Thread.Sleep(1000);
 Random r=new Random();
 int n=r.Next(10);
 if (n==5)
 {
     num=r.Next(1000);
 }
 handles[i].Set();
}

Get more information on http://msdn.microsoft.com/en-us/library/z6w25xa6.aspx

answered Jul 01 '13 at 13:43

Ivan Manzhos

743
6
12

Rather than having n MRE's you could just have one semaphore initialized with a value of N; it would be simpler. Although just using `Thread.Join` or `Thread.WaitAll` would likely be simpler still. – Servy Jul 01 '13 at 14:08

Shumail · Answer 3 · 2013-07-01T14:05:32.753

0

I think you can use Thread.WaitAll(thread_array) or in other case you can also use Thread.Sleep(100)

In Thread.sleep, 100 is number of milliseconds. So in this case thread would sleep for 100 milliseconds.

And in Thread.WaitAll - thread_Array is array of threads that you wanna wait.

edited Jul 01 '13 at 14:05

answered Jul 01 '13 at 13:53

Shumail

3,103
4
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Real software doesn't `Sleep()`. It's certainly no replacement for Join/Wait. – H H Jul 01 '13 at 14:17

score 0 · Answer 4 · edited May 23 '17 at 11:56

As this question is effectively a duplicate, please see this answer, (code copied below, all credit to Reed Copsey.

class Program
{
    static void Main(string[] args)
    {
        int numThreads = 10;
        ManualResetEvent resetEvent = new ManualResetEvent(false);
        int toProcess = numThreads;

        // Start workers.
        for (int i = 0; i < numThreads; i++)
        {
            new Thread(delegate()
            {
                Console.WriteLine(Thread.CurrentThread.ManagedThreadId);
                // If we're the last thread, signal
                if (Interlocked.Decrement(ref toProcess) == 0)
                    resetEvent.Set();
            }).Start();
        }

        // Wait for workers.
        resetEvent.WaitOne();
        Console.WriteLine("Finished.");
    }
}

Aside

Also note that your PasswdThread code will not produce random numbers. The Random object should be declared statically, outside of your method, to produce random numbers.

Additionally you never use the int i parameter of that method.

jamespconnor · Answer 5 · 2013-07-01T14:30:34.833

I would use TPL for this, imo it's the most up to date technique for handling this sort of synchronization. Given the real life code is probably more complex, I'll rework the example slightly:

public int GetValue()
{
    List<Task<int>> tasks = new List<Task<int>>();
    for (int i = 0; i <=5; i++)
    {
        tasks.Add(PasswdThread(i));
    }

    Task.WaitAll(tasks);

    // You can now query all the tasks:
    foreach (int result in tasks.Select(t => t.Result))
    { 
        if (result == 100) // Do something to pick the desired result...
        {
            return result;
        }
    }

    return -1;
}

public Task<int> PasswdThread(int i)
{
    return Task.Factory.StartNew(() => {
        Thread.Sleep(1000);
        Random r=new Random();
        int n=r.Next(10);
        if (n==5)
        {
            return r.Next(1000);
        }
        return 0;
    });
}

No! I can't use Task because it's a lot of problem with write file from thread. — Jon Maximys, Jul 01 '13 at 15:37

score -1 · Answer 6 · answered Jul 01 '13 at 13:58

-1

    Thread t=null;
List<Thread> lst = new List<Thread();
    for (int i = 0; i <=5; i++)
    {
         t = new Thread(() => PasswdThread(i));
         lst.Add(t);
         t.Start();  
    }

    //how wait all thread, and than return value?   
foreach(var item in lst)
{
    while(item.IsAlive)
    {
         Thread.Sleep(5);
    }
}
    return num;

answered Jul 01 '13 at 13:58

Marguth

191
9

You shouldn't be using a busywait; there are tools given to you to avoid needlessly consuming so many additional resources doing this. – Servy Jul 01 '13 at 14:31

How wait all thread

6 Answers6

Aside