hendra.dev - Threading in C#

Well, this time, I am going to talk about thread, the concept of thread is pretty simple to understand, so I wont explain the here, but you can read more about it in this wiki page. Threading are used quite extensively in most modern computer programs, for example separating threads to handle button clicks on a GUI button from the one that handles data processing, or in chatting programs, where it separates threads to send messages from the one that handles incoming messages and display it on the screen.

In .NET, threading is handled by the Thread class, which lives in the System namespace, so to use it, you need to add this first:

:::csharp
using System.Threading;

To create a new thread, we need to create a new Thread instance, which takes a delegate of type ThreadStart (remember that delegate is like a pointer to a method? this would mean that the thread will run the method that the delegate parameter points to.). ThreadStart itself is a delegate that does not return any value or accept any parameter. Here is an example:

:::csharp
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            ThreadStart someCode = delegate() { for (int i = 0; i < 5;i++)Console.WriteLine(i); };
            Thread t1 = new Thread(someCode);
            Thread t2 = new Thread(someCode);
            Thread t3 = new Thread(someCode);

            t1.Start();
            t2.Start();
            t3.Start();

            someCode();
            Console.Read();
        }
    }
}

You will see that the each number will be printed 4 times, but in no particular order, the operating decides which threads gets run at any given time, but you can see that the same method is being run in 4 different threads. The three threads that we created with the Thread class, and the main thread of the program itself.

In the example above, the threads are all accessing local variables, that is, they don’t share any data between them. This makes things pretty simple, but there are times where the threads are accessing a shared data, and this may cause a problem known as race condition. To prevent, that, we need a way sync the data by locking the data to a thread during a section of the program that may cause a race condition. In .NET, the Threading namespace provides us with a Monitor class that we can use to lock an object. Here is an example.

:::csharp
var sharedData = new SomeClass();

// lock the sharedData
Monitor.Enter(sharedData);

// Write the critical codes here.
// Codes between the Enter and Exit can only be performed by one thread
// at a time,

// release the sharedData
Monitor.Exit(sharedData);

Thread synchronization is pretty complicated topic, I think will cover them in another post some time later, when I got a better understanding of it. Here is an MSDN article on the topic.

The Thread class provides several methods to control the execution of the thread, here are some of them:

:::csharp
// these examples are called from within the execution of another thread
// e.g. t2

// Pausing the current thread execution for 2 seconds
Thread.Sleep(1000);

// Wait for t1 thread to finish executing
t1.Join();

// stop the execution of a thread
t1.Abort();

// pause the thread
t1.Suspend();

// resume the thread
t1.Resume();

// accessing the thread state
t1.ThreadState

C# also provides some methods to control the execution of another process via the Process class in the System.Diagnostics namespace, but I’m not too concerned about that for now, so this post ends here.

References: