Zitat:

'Now what is a mutex? A mutex object is a synchronization object whose state is set to 'signaled when it is not owned by any thread, and nonsignaled when it is owned. Only one 'thread at a time can own a mutex object, whose name comes from the fact that it is 'useful in coordinating mutually exclusive access to a shared resource. Now, how this 'method of avoiding multiple instances works is explained in the comments below. Enjoy.