Usage of Mutex in c#

c# multithreading mutex
Nadav picture Nadav · Apr 22, 2011 · Viewed 63.4k times · Source

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

Marc Gravell picture Marc Gravell · Apr 22, 2011

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();
    }
}

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