Mutex

What is it?

Mutex stands for Mutual Exclusion, and it’s used in Multi-Threading applications and Distributed Computing systems to handle situations like Livelocks, Deadlocks and any Race Condition.

Mutex is explicitly set by the programmer to ensure that only the first thread is allowed to use the resource, and others threads need to wait until the first is complete and unset the mutex. Think of it like a gate which only allows one thread to use a resource at a time.

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How does it work?

A mutex implementation is basically a flag which a thread will set when beginning to use the resource, and unsetting it when it completes. This way, all other threads wait for the mutex and they will perform the the set-unset work when using the resource.

using System;
using System.Threading;
 
class Program
{
    static Mutex mutex = new Mutex();
 
    static void Main()
    {
        for (int i = 1; i <= 5; i++)
        {
            Thread t = new Thread(DoWork);
            t.Name = $"Thread {i}";
            t.Start();
        }
    }
 
    static void DoWork()
    {
        Console.WriteLine($"{Thread.CurrentThread.Name} is waiting");
 
        mutex.WaitOne();  // Wait until it can enter the critical section
        try
        {
            Console.WriteLine($"{Thread.CurrentThread.Name} has entered");
            Thread.Sleep(1000);  // Simulate some work
            Console.WriteLine($"{Thread.CurrentThread.Name} is leaving");
        }
        finally
        {
            mutex.ReleaseMutex();  // Always release the mutex
        }
    }
}