Using Monitor Class

Question

Dear All

I would like to ask couple of Questions regarding the use of Monitor Class in .Net.

To understand the Questions please look at the following Code.

public class MyClass
{
    private List<int> _MyCollection = new List<int>();

    public void GetLock()
    {
        Monitor.Enter(_MyCollection);
    }

    public void ReleaseLock()
    {
        Monitor.Exit(_MyCollection);
    }

    public void UpdateCollection(/*anyparam*/)
    {
        //update collection without lock on collection
    }
}

public class MyAppMain
{
    private static MyClass myclass = new MyClass();

    public static void main(args)
    {
        try
        {
            myclass.GetLock();

            //an operation that does not do any update on myclass but wanted 
            //to ensure that the collection within myclass never update
            //while its doing following opetion

            //Do somthing
        }
        finally
        {
            myclass.ReleaseLock();
        }
    }
}

Now is this the right use of monitor and do i need to use Pulse or PulseAll to signal waiting thread and if so than should use plus before or after Exit function?

Regards Mubashar

Answer 1

Obtaining your lock and then releasing it in a finally block is correct. I'd get the lock before the try block starts but it probably won't hurt anything unless an exception gets thrown by the attempt to obtain the lock.

For what you are actually trying to do, you are going to need to rethink what your goal is. Depending on whether or not performance is a concern, you might look into the ReaderWriterLock. If contention is low, consider locking every operation but using a spin lock - which is extremely cheap for operations that do not tend to overlap but might.

Also: I think you need to revisit the notion of updating the collection without locking unless you can ensure that only one thread will be updating the collection.

Answer 2

Yes, your usage of Monitor is correct.

That said, you can use the lock statement to make the code more concise:

public static void main(args)
{
    lock(myclass)
    {
    }
}