Usage of Mutex in c#

Question

I am a bit new in threading in c# and on general, in my program I am using mutex to allow only 1 thread getting inside a critical section and for unknown reason with doing some cw prints I can see that more than 1 thread is getting inside my critical section and this is my code :

Mutex m = new Mutex(); m.WaitOne(); <C.S> // critical section here m.ReleaseMutex(); 

I would very much like to know if I am doing a mistake here thanks in advance for your kind help.

EDIT:

My code include classes so it basically looks more like this:

public class test {     private mutex m;     public test()     {          m = new mutex();     }     public func()     {          m.WaitOne();          <C.S> // critical section here          m.ReleaseMutex();      }       }  

Answer 1

The problem here is that all your callers are using a different mutex; you need the locking object to be shared, usually by making it a field. For example, and switching to a simpler lock metaphor:

private readonly object syncLock = new object(); public void ThreadSafeMethod() {     lock(syncLock) {         /* critical code */     } } 

or using the mutex:

private readonly Mutex m = new Mutex(); public void ThreadSafeMethod() {     m.WaitOne();     try {         /* critical code */     } finally {         m.ReleaseMutex();     } } 

Answer 2

It looks like you give each Thread its own Mutex. That won't work.

And a Mutex is overkill in most situations. You only need:

private static object syncLock = new object();  // just 1 instance  ....  lock(syncLock) {     // critical section }