How to Pass Parameters to Threadstart Method in Thread

How to pass parameters to ThreadStart method in Thread?

The simplest is just

string filename = ...
Thread thread = new Thread(() => download(filename));
thread.Start();

The advantage(s) of this (over ParameterizedThreadStart) is that you can pass multiple parameters, and you get compile-time checking without needing to cast from object all the time.

ThreadStart with parameters

Yep :

Thread t = new Thread (new ParameterizedThreadStart(myMethod));
t.Start (myParameterObject);

How to pass parameters to a thread in C#?

The problem with that code is that ParameterizedThreadStart is a delegate type, which means it is tied to a specific method signature -- in particular, that signature is void method(object). Your method Thread2 does not match that signature, hence the compiler error.

So how to solve it? It depends really.

ParameterizedThreadStart has that signature because it's the most generic approach ever. The idea behind it is that you can pass an object of some custom type that contains all the state your function needs, like this:

class Params
{
    public int Start { get; set; }
    public int End { get; set; }
    public int[] Array { get; set; }
}

var p = new Params { 0, 0, new int[0] };
var t = new Thread(thr2.Thread2);
t.Start(p);

public int Thread2(object param)
{
    var p = (Params)param;
    // and now get your arguments as p.Start etc.
}

While this works, it's unwieldy and forces you to abandon the most natural signature for Thread2. But you can do better by interposing an anonymous function to do the unpacking of arguments:

int start = 0, end = 0;
var arr = new int[0];
var t = new Thread(() => thr2.Thread2(start, end, arr));

If you choose to do this you have to be mindful of the fact that due to the mechanism the compiler uses to pass the arguments to the thread method, changing their values after t is defined but before it is started will make Thread2 see the changed values.

Pass Parameters through ParameterizedThreadStart

lazyberezovsky has the right answer. I want to note that technically you can pass an arbitrary number of arguments using lambda expression due to variable capture:

var thread = new Thread(
       () => DoMethod(a, b, c));
thread.Start();

This is a handy way of calling methods that don't fit the ThreadStart or ParameterizedThreadStart delegate, but be careful that you can easily cause a data race if you change the arguments in the parent thread after passing them to the child thread's code.

Passing parameter inside thread start

You can try

 int value = 123;
 fail objfail = new fail();
 var t = new Thread(() => objfail.DoWork(value));
 t.Start();

passing parameters to a thread

You need ParametrizedThreadStart to pass a parameter to a thread.

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

ThreadStart with Parameter method

Thread t = new Thread(new ParameterizedThreadStart(loop));
t.Start("Hello world");

private void loop(object obj)
{
    string str = (string)obj;

    for (int i = 0; i < 100000; i++)
    {
        // Don't do this: you can't change a control from another thread. Danger Will Robinson!
        textBox1.Text = i + str;
    }
}

Note that the loop method must accept an object parameter, so you'll have to upcast the object to your type. If you don't want, you can use a closure and an anonymous method:

string str = "Hello world";
Thread t = new Thread(() => {
    for (int i = 0; i < 100000; i++)
    {
        // Don't do this: you can't change a control from another thread. Danger Will Robinson!   
        textBox1.Text = i + str;
    }
});
t.Start();

In this way the anonymous method will "close" around str and it will be similar as if you had passed the parameter. Similar because there are differences/problems on closing variables. In reality I would write something similar to:

string str = "Hello world";

{
    string str2 = str;

    Thread t = new Thread(() => {
        for (int i = 0; i < 100000; i++)
        {
            // Don't do this: you can't change a control from another thread. Danger Will Robinson! 
            textBox1.Text = i + str2;
        }
    });

    t.Start();
}

so that no one else can "touch" str2.

If you need I can find some answer on SO that explain this "problem"

---

Related Topics