Question

How can I create a system/multiprocess Mutex to co-ordinate multiple processes using the same unmanaged resource.

Background:
I’ve written a procedure that uses a File printer, which can only be used by one process at a time. If I wanted to use it on multiple programs running on the computer, I’d need a way to synchronize this across the system.

Answer 1

There is a constructor overload for checking for an existing mutex.

http://msdn.microsoft.com/en-us/library/bwe34f1k(v=vs.90).aspx

So…

void doWorkWhileHoldingMutex()
{
    Console.WriteLine("   Sleeping...");
    System.Threading.Thread.Sleep(1000);
}

var requestInitialOwnership = true;
bool mutexWasCreated;
Mutex m = new Mutex(requestInitialOwnership, 
         "MyMutex", out mutexWasCreated);

if (requestInitialOwnership && mutexWasCreated)
{
    Console.WriteLine("We own the mutex");
}
else
{
    Console.WriteLine("Mutex was created, but is not owned. Waiting on it...");
    m.WaitOne();
    Console.WriteLine("Now own the mutex.");
}
doWorkWhileHoldingMutex();
Console.WriteLine("Finished working. Releasing mutex.");
m.ReleaseMutex();

If you fail to call m.ReleaseMutex() it will be called ‘abandoned’ when your thread exits. When another thread constructs the mutex, the exception System.Threading.AbandonedMutexException will be thrown telling him it was found in the abandoned state.