Exit a method if another thread is executing it

Question

I have a method in a multi-threaded application and I'd like the following behavior when this method is invoked:

1. If no other threads are currently executing the method, execute it.
2. If another thread is currently executing the method then exit the method without executing it.

The lock statement in C# is useful for waiting until a thread has completed execution, but I don't want to serialize access to this method but rather bypass executing said method if it is being executed by another thread.

Answer 1

You can do this using Monitor.TryEnter, but perhaps more simply: Interlocked:

int executing; // make this static if you want this one-caller-only to
               // all objects instead of a single object
void Foo() {
    bool won = false;
    try {
        won = Interlocked.CompareExchange(ref executing, 1, 0) == 0;
        if(won) {
           // your code here
        }
    } finally {
        if(won) Interlocked.Exchange(ref executing, 0);
    }

}