Concurrence among C# threads

Question

The scenario is the following one:

public class MainClass

    {

           private static Object common_object;

           protected int Method_A()
           {

             ...

             lock (common_object)
                 {

                     // Works with common_object;

                     ...

                 }

             ...

             // Invokes another's thread Method_B

           }

           protected int Method_B()
           {
             ...

           }

    }

I have a Class: "Main Class", and 2 (or more) instances of it.

The Class has an object (private, static) wich is shared by every instance and protected using "lock(){...}" where needed. I have no problems with it.

The Class has also 2 methods wich are the ones are making me going crazy trying to make everything work.

Let's say there is the "main method/function", A, wich is invoked from the outside (I have no control over this invokations, nor knowledge of when is going to occur, but it's almost all the time with really short spaces between one invokation and the next one) on both threads.

There's also a second method, B, much shorter (both in time of execution and in code).

Here is the problem:

t2 invokes method A

t1 invokes method A

t2 (from method A) invokes t1's method B

t1 and t2 are blocked.

The method B of one thread(t2) is invoked from the method A of the other thread(t1), and if it is done when t2 is executing method A, everything crashes in one way or another. Usually both of the threads get blocked.

I'm using a flag-variable, so when t2 begins to execute method A, this flag is used by t1 to know he can't invoke t2's method B until t2 finishes the method A execution, but it seems I'm missing something because it doesn't work.

I'm used to work with Java, and thoung I guess there's the exactly same logic behing C# code, I think that there must be some functions or "tricks" in c# I am missing.

I guess (and hope) that there must be an easy way to solve this problem, since it's not a mayor one, and so I am finally here, asking for help after 3 days with no significative advances on my own.

Thanks in advance.

Answer 1

Well, as terrybozzio suggested, it was about placing the eventwaithandles methods (wait, pulse) in the wrong place. Problem solved.

Thanks for the tip.

Answer 2

I think you're getting confused here. You've only got one class and one object. Threads don't have their own copies of methods. When Method_A calls Method_B it's all on one thread. Also: flags are very tricky to use. You haven't put one in your example, so I can't say specifically what you're doing wrong, but I've never gotten them right on the first try. (Or the second.) Best to avoid them if you can.

In this case, I think all you need to do is put the call to Method_B inside the common_object lock block.

And as far as I can see, everything you are doing works the same in C# as in Java.