[Opensim-dev] .NET / Mono lock(obj) statement

[Hurliman, John]

C# treats a monitor (lock statement) the same as Java. The same thread can reenter a lock as many times as it wishes. The following code completes as expected on .NET 3.5 SP1, Mono 1.9.1 (Windows), and Mono 1.9.1 (Ubuntu 8.10 AMD64):

using System;

namespace sandbox
{
    class Program
    {
        static void Main(string[] args)
        {
            object a = new object();

            Console.WriteLine("Starting");

            lock (a)
            {
                Console.WriteLine("Inside Main() lock");

                lock (a)
                {
                    Console.WriteLine("Inside second Main() lock");

                    F(a);
                }
            }

            Console.WriteLine("Done");
        }

        static void F(object a)
        {
            Console.WriteLine("Inside F()");

            lock (a)
            {
                Console.WriteLine("Inside F() lock");
            }
        }
    }
}



> -----Original Message-----
> From: opensim-dev-bounces at lists.berlios.de [mailto:opensim-dev-
> bounces at lists.berlios.de] On Behalf Of Diva Canto
> Sent: Tuesday, January 13, 2009 8:58 PM
> To: opensim-dev at lists.berlios.de
> Subject: [Opensim-dev] .NET / Mono lock(obj) statement
>
> Hi everyone,
>
> Just got back from vacation to TP grief caused by extra locking
> introduced in 7982. The extra locking is all good, but it seems that
> certain things confuse the heck out of mono, so I thought I'd bring up
> the issue here -- I'm pretty sure this problem occurs in other places
> of the code too, so it's good to know what to expect. I'd certainly
> like to find out more about the .NET spec.
>
> Here's a simplified version of the problem:
>
> lock (a)
> {
>    foo();
> }
>
> void foo()
> {
>   lock (a)
>   {
>     ...
>   }
> }
>
> (the real situation is a bit more complicated; foo() involves a
> delegate; but ignore that)
>
> In Java, this situation does NOT result in locking, because it's the
> same thread that's acquiring object a. I can't find the spec for .NET
> for this particular issue, but I'd be very surprised if it is
> different from Java. Nevertheless, mono was deadlocking here; Windows
> was not. I find the mono behavior very strange.
>
> Crista
>
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