How to create a thread in C#?

Threads are lightweight processes that represent independent execution paths within a program. In C#, threads are created using the Thread class from the System.Threading namespace. Creating threads enables concurrent programming, allowing multiple operations to run simultaneously and improving application efficiency.

Modern operating systems use threads to implement concurrent programming, which saves CPU cycles and increases application performance by allowing multiple tasks to execute in parallel.

Syntax

Following is the basic syntax for creating a thread in C# −

Thread threadName = new Thread(methodName);
threadName.Start();

You can also use a ThreadStart delegate to wrap the method −

ThreadStart threadDelegate = new ThreadStart(methodName);
Thread threadName = new Thread(threadDelegate);
threadName.Start();

Creating a Basic Thread

The following example demonstrates how to create and start a simple thread −

using System;
using System.Threading;

namespace Demo {
    class Program {
        public static void ThreadFunc() {
            Console.WriteLine("Child thread starts");
            Console.WriteLine("Child thread executing...");
            Console.WriteLine("Child thread ends");
        }
        
        static void Main(string[] args) {
            ThreadStart childref = new ThreadStart(ThreadFunc);
            Console.WriteLine("In Main: Creating the Child thread");
            Thread childThread = new Thread(childref);
            childThread.Start();
            Console.WriteLine("Main thread continues...");
        }
    }
}

The output of the above code is −

In Main: Creating the Child thread
Main thread continues...
Child thread starts
Child thread executing...
Child thread ends

Creating Thread with Parameters

You can pass parameters to a thread using ParameterizedThreadStart delegate −

using System;
using System.Threading;

namespace Demo {
    class Program {
        public static void ThreadWithParam(object data) {
            string message = (string)data;
            Console.WriteLine("Thread received: " + message);
            for (int i = 1; i <= 3; i++) {
                Console.WriteLine("Thread iteration: " + i);
                Thread.Sleep(1000);
            }
        }
        
        static void Main(string[] args) {
            ParameterizedThreadStart threadStart = new ParameterizedThreadStart(ThreadWithParam);
            Thread paramThread = new Thread(threadStart);
            Console.WriteLine("Starting parameterized thread");
            paramThread.Start("Hello from Main!");
            Console.WriteLine("Main thread finished");
        }
    }
}

The output of the above code is −

Starting parameterized thread
Main thread finished
Thread received: Hello from Main!
Thread iteration: 1
Thread iteration: 2
Thread iteration: 3

Using Lambda Expressions

Modern C# allows creating threads using lambda expressions for simpler syntax −

using System;
using System.Threading;

namespace Demo {
    class Program {
        static void Main(string[] args) {
            Console.WriteLine("Main thread starting");
            
            Thread lambdaThread = new Thread(() => {
                Console.WriteLine("Lambda thread executing");
                for (int i = 1; i <= 3; i++) {
                    Console.WriteLine("Count: " + i);
                    Thread.Sleep(500);
                }
                Console.WriteLine("Lambda thread completed");
            });
            
            lambdaThread.Start();
            Console.WriteLine("Main thread continues");
            lambdaThread.Join(); // Wait for thread to complete
            Console.WriteLine("All threads finished");
        }
    }
}

The output of the above code is −

Main thread starting
Main thread continues
Lambda thread executing
Count: 1
Count: 2
Count: 3
Lambda thread completed
All threads finished

Thread Methods

Conclusion

Creating threads in C# enables concurrent programming and improves application performance. You can create threads using the Thread class with method delegates, parameters, or lambda expressions. Always consider using Join() to coordinate thread completion when needed.