How do I pass arguments to a Thread in .Net

Question

I have function along these lines:

public void view(string msg)
{
  messagebox.show(msg);
}
.

.

I want to pass arguments to this it from a thread.. I'm using .Net 1.1. How can I do this?

Answer 1

For .NET 1.1 there is no direct way but to use an object having both the method and the state, in this example (modified from the MSDN sample), the ThreadState class is instanced and passed the desired state, then its method is called and made to use the passed state.

public class ThreadState {
    private string msg;

    // The constructor obtains the state information.
    public ThreadState(string msg) {
        this.msg = msg;
    }

    public void view() {
        //Do something with msg
    }
}

public class Example {
    public static void Main() {
        ThreadState ts = new ThreadState("Hello World!");
        // Create a thread to execute the task, and then
        // start the thread.
        Thread t = new Thread(new ThreadStart(ts.view));
        t.Start();
        t.Join();
    }
}

For .NET > 1.1 (original question didn't state version.)

You pass the argument in the Start method. You will receive an object which you need to cast back to the proper type.

Thread t = new Thread(view);
t.Start("Hello");

public void view(object msg) 
{
     string m = (string)msg;
     //Use msg
}

Either that, or use a ParameterizedThreadStart delegate.

Answer 2

There are various ways to do that. One is to use the ParameterizedThreadStart delegate, which allows passing a single parameter of type Object to the thread. Change your view method to accept Object, then cast Object to String inside the method.

Answer 3

The ParamaterizedThreadStart delegate is not present in .NET 1.1 (2003) nor does thread.Start take an Object param in 1.1. However you could try something like:

dict[mythread.name] = myval; //dict is a class scoped variable.
mythread.Start();

Answer 4

The first code snippet provided by Vinko is exactly what you need under .NET 1.x as the original Threading namespace offered no in-built mechanism for parameterizing _beginthread.

Thus, you create a state class which contains the data you need, as well as the method which will be used for the delegate in the "new Thread()" statement, as Vinko has shown.

I was about to tap out a sample, and then I saw his sample code. If it's "not working" it's worth being explicit as to why, because by the naked eye that code looks all too familiar.

One "spin" on this is to properly encapsulate the thread construction as well as the thread start/join behavior.

Another option is to use ThreadPool.QueueUserWorkItem(), which isn't quite the same and can result in poor ThreadPool performance if over-used.

Another option is to create a thread that is blocked on a signal, e.g. ManualResetEvent, which is set when a data member has been initialized. The target data member can be as simple as an object reference as shown above, or you could use an ArrayList, Queue or Stack object (with proper locking) to implement a sort of "queue processor" where work items can be enqueued and processed by a dedicated thread, and where the dedicated thread remains dormant (blocked waiting for a signal) until there is work available.

Answer 5

Create a class, set your properties as arguments and run related function of the class.

Dim run = New Runner()
run.mile = 20
run.pace = "slow"
Thr.Start(run.Process())

Or you need to use a global scope variable. Unfortunately no other way for .NET 1.1