passing parameters to a thread

Question

I want to pass a function that takes a parameter to the ThreadStart Constructor in C#. But, it seems that this is not possible, as I get a syntax error it I try to do something like this

Thread t1 = new Thread(new ThreadStart(func1(obj1));

where obj1 is an object of type List<string> (say).

If I want a thread to execute this function that takes in an object as a parameter, and I plan to create 2 such threads simultaneously with different parameter values what is the best method to achieve this?

Wow! I did this before by creating a class to contain data that the thread will use, but I had no idea there were so many different ways to skin this animal! — Vivian River, May 11 '10 at 17:01

score 13 · Answer 1 · answered May 11 '10 at 16:55

13

If you're using .NET 3.5 or higher, one option is to use a lambda for this:

var myThread = new System.Threading.Thread(() => func1(obj1));

answered May 11 '10 at 16:55

Mark Rushakoff

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score 8 · Accepted Answer · answered May 11 '10 at 16:56

8

You need ParametrizedThreadStart to pass a parameter to a thread.

Thread t1 = new Thread(new ParametrizedThreadStart(func1);
t1.Start(obj1);

answered May 11 '10 at 16:56

Thomas

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Thanks a lot.. this method works.. however, the definition for func1 in this case will have to be void func1(object state) and cannot be void func1(List obj1) why is this the case? – assassin May 12 '10 at 05:05
That's how the `ParametrizedThreadStart` delegate type is defined. You'll have to cast the `object` back to `List` inside `func1`. – Thomas May 12 '10 at 06:34

score 7 · Answer 3 · answered May 11 '10 at 16:56

7

You can start a new thread like this:

Thread thread = new Thread(delegate() {
    // Code here.
});
thread.Start();

Inside the anonymous method you have access to the variables that were in scope when the delegate was created.

answered May 11 '10 at 16:56

Mark Byers

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score 3 · Answer 4 · answered May 11 '10 at 16:55

Try this:

var bar = 0.0;
Thread t = new Thread(() => 
    {
        Foo(bar);
    });
t.IsBackground = true;
t.Start();

Or in your case:

Object obj1 = new Object();
Thread t = new Thread(() => 
    {
        func1(obj1);
    });
t.IsBackground = true;
t.Start();

JMarsch · Answer 5 · 2010-05-12T14:07:39.347

3

Edit Assassin had trouble getting this code to work, so I have included a complete example console app at the end of this post.



{ // some code
  Thread t1 = new Thread(MyThreadStart);
  t1.Start(theList);
}

void MyThreadStart(object state)
{
  List<string> theList = (List<string>)state;
  //..
}

This is my edit: Below is a complete console app -- the technique really does work:


using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            System.Threading.Thread t = new System.Threading.Thread(MyThreadStart);
            t.Start("Hello");
            System.Console.ReadLine();
        }


        static void MyThreadStart(object state)
        {
            System.Console.WriteLine((string)state);
        }
    }
}

edited May 12 '10 at 14:07

answered May 11 '10 at 16:56

JMarsch

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This doesn't work.. i tried it... the ParametrizedThreadStart method suggested by Thomas works. – assassin May 12 '10 at 05:03
@assassin I assure you, it does work. I have edited my entry to include a console app that you can paste directly into Visual Studio and run. This syntax has worked since .Net 2.0, and if you replace the "new Thread(MyThreadStart)" with "new Thread(new delegate – JMarsch May 12 '10 at 14:05

score 3 · Answer 6 · answered May 11 '10 at 17:05

Is this the effect you're looking for?

        static void Main(string[] args)
    {
        var list = new List<string>(){
            "a","b","c"
        };

        Thread t1 = new Thread(new ParameterizedThreadStart(DoWork));

        t1.Start(list);

        Console.ReadLine();

    }

    public static void DoWork(object stuff)
    {
        foreach (var item in stuff as List<string>)
        {
            Console.WriteLine(item);
        }
    }

score 1 · Answer 7 · answered May 11 '10 at 17:07

static void func1(object parameter)
{
   // Do stuff here.
}

static void Main(string[] args)
{
  List<string> obj1 = new List<string>();
  Thread t1 = new Thread(func1);
  t1.Start(obj1);
}

It's using a new delegate in .Net 2.0 called ParameterizedThreadStart. You can read about it here.

score 0 · Answer 8 · answered May 11 '10 at 16:58

0

See ParameterizedThreadStart

answered May 11 '10 at 16:58

KMån

9,896
2
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score 0 · Answer 9 · answered May 11 '10 at 18:59

Do you absolutely need to use a Thread object? Or are you just looking for multithreaded processing to happen? A more "modern" approach would be to use an asynchronous delegate as such:

private delegate void FuncDelegate(object obj1);
.
.
.
FuncDelegate func = func1;
IAsyncResult result = func.BeginInvoke(obj1, Completed, func);

// do other stuff
.
.
.

private void Completed(IAsyncResult result)
{
    ((FuncDelegate)result.AsyncState).EndInvoke(result);

    // do other cleanup
}

An even more "modern" method would be to use Tasks in the .NET 4 TPL.

passing parameters to a thread

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