C# thread functions

Question

Can i make any function like

public void myfunc()
{
   //some processing
}

a thread function by

Thread t = new Thread (new ThreadStart (myfunc));

then some where

t.Start();

and can i pass any type of arguments to that?

Answer 1

In theory you can make any method execute in a separate thread, as long as you follow some rules (e.g. synchronization, invoke delegates to update ui, etc.).

From your question I understand that you do not have much experience with multi threaded programming, so I advise you to read a lot about threading and learn about the dangers and problems that can arise. You may also use the background worker class that take some of the responsibilities from you.

Also, yes, you can pass parameters to a thread method:

private class ThreadParameters
{
   ....
}

...

public void ThreadFunc(object state)
{
    ThreadParameters params = (ThreadParameters)state;
    ....
}

Thread t = new Thread(new ParameterizedThreadStart(ThreadFunc));
t.Start(new ThreadParameters() { ... });

Answer 2

There is an overload that accepts an object state - however, IMO the easiest way to pass arbitrary arguments to a threadstart (and verify the signature at compile time) is with an anonymous method:

int a = ...
string b = ...
Thread t = new Thread (delegate() { SomeFunction(a,b);});

Just (and this is important) - *don't change a or b after this, as the change will be reflected to the thread (as a race) - i.e. don't do:

int a = ...
string b = ...
Thread t = new Thread (delegate() { SomeFunction(a,b);});
a = 12; // this change will be visible to the anonymous method - be careful ;-p

In the case of loops, it is important (when dealing with async and captured variables) to introduce extra variables for this; these are very different

    int[] data = {1,2,3,4,5};
    foreach(int i in data) {
        ThreadPool.QueueUserWorkItem(delegate {
            Console.WriteLine(i); });
    }
    Console.ReadLine();

(which will probably print 5,5,5,5,5)

    int[] data = {1,2,3,4,5};
    foreach (int i in data) {
        int tmp = i;
        ThreadPool.QueueUserWorkItem(delegate {
            Console.WriteLine(tmp); });
    }
    Console.ReadLine();

(which will print 1-5 in no particular order)

---

Update to discuss Meeh's point (comments); what does this print (99.999% of the time - there is a race condition)?

    string s = "dreams";
    ThreadPool.QueueUserWorkItem(delegate {
        Console.WriteLine(s);
    });
    s = "reality";
    Console.ReadLine();

Answer 3

Check here: http://www.yoda.arachsys.com/csharp/threads/parameters.shtml

Or here, using thread pool: http://www.yoda.arachsys.com/csharp/threads/threadpool.shtml