Can I put a return statement inside a lock

Question

Dupe: return statement in a lock procedure: inside or outside

The title is a little misleading. I know that you can do it, but I\'m wondering about

Answer 1

Yes, but why not use Dequeue?

Remember lock is simply shorthand for essentially something along the lines of:

        try
        {
            Monitor.Enter(QueueModifierLockObject);

            DownloadFile toReturn = queue.Dequeue();         

            return toReturn;
        }
        finally
        {
            Monitor.Exit(QueueModifierLockObject);
        }

Answer 2

The C# compiler will move the return statement outside of the try/finally that is created for the lock statement. Both of your examples are identical in terms of the IL that the compiler will emit for them.

Here is a simple example proving that:

class Example
{
    static Object obj = new Object();

    static int Foo()
    {
        lock (obj)
        {
            Console.WriteLine("Foo");
            return 1;
        }
    }

    static int Bar()
    {
        lock (obj)
        {
            Console.WriteLine("Bar");
        }
        return 2;
    }
}

The code above gets compiled to the following:

internal class Example
{
        private static object obj;

        static Example()
        {
                obj = new object();
                return;
        }

        public Example()
        {
                base..ctor();
                return;
        }

        private static int Bar()
        {
                int CS$1$0000;
                object CS$2$0001;
                Monitor.Enter(CS$2$0001 = obj);
        Label_000E:
                try
                {
                        Console.WriteLine("Bar");
                        goto Label_0025;
                }
                finally
                {
                Label_001D:
                        Monitor.Exit(CS$2$0001);
                }
        Label_0025:
                CS$1$0000 = 2;
        Label_002A:
                return CS$1$0000;
        }

        private static int Foo()
        {
                int CS$1$0000;
                object CS$2$0001;
                Monitor.Enter(CS$2$0001 = obj);
        Label_000E:
                try
                {
                        Console.WriteLine("Foo");
                        CS$1$0000 = 1;
                        goto Label_0026;
                }
                finally
                {
                Label_001E:
                        Monitor.Exit(CS$2$0001);
                }
        Label_0026:
                return CS$1$0000;
        }
}

As you can see, the compiler has taken the libery of moving the return statement in Foo outside of the try/finally.

Answer 3

I believe the IL would be identical... I'd have to test it to be fer sure, but the lock statement generates a try finally in the IL, and the return would trigger the finally (with the release) BEFORE the stack frame closes and returns to the caller anyway, so...