[IronPython] Ironclad problem, with which someone here may be able to help

[Curt Hagenlocher]

So, the obvious question for me is whether or not you're using any
finalizers.

On Wed, Nov 5, 2008 at 5:57 AM, William Reade
<william at resolversystems.com>wrote:

> Hi all
>
> While running the numpy tests, I've come across a situation which, to the
> best of my knowledge, is simply impossible. I'm hoping that one of the local
> .NET gurus will be able to tell me what I'm missing, or point me somewhere I
> can get more insight.
>
> The 4 methods involved are as follows:
> -----------------------
>       public int GetThreadId()
>       {
>           return Thread.CurrentThread.ManagedThreadId;
>       }
>
>       public void WriteFlush(string info)
>       {
>           Console.WriteLine(info);
>           Console.Out.Flush();
>       }
>
>       public void EnsureGIL()
>       {
>           Monitor.Enter(this.dispatcherLock);
>           this.WriteFlush(String.Format(
>               "EnsureGIL ({1}) {0}", this.GetThreadId(),
> Builtin.id(this.dispatcherLock)));
>       }
>
>       public void ReleaseGIL()
>       {
>           this.WriteFlush(String.Format(
>               "ReleaseGIL ({1}) {0}\n", this.GetThreadId(),
> Builtin.id(this.dispatcherLock)));
>           Monitor.Exit(this.dispatcherLock);
>       }
> -----------------------
> ...and they can, and do, occasionally produce output as follows:
> -----------------------
> EnsureGIL (443) 2
> EnsureGIL (443) 1      <- omg, wtf, bbq, etc.
> ReleaseGIL (443) 2
>
> EnsureGIL (443) 2
> ReleaseGIL (443) 1
>
> ReleaseGIL (443) 2
> -----------------------
> When this happens, the process continues happily for a short time and then
> falls over in a later call to ReleaseGIL (after successfully calling it
> several times). The error is " Object synchronization method was called from
> an unsynchronized block of code", which I understand to mean "you can't
> release this lock because you don't hold it".
>
> It doesn't happen very often, but I can usually reproduce it by running
> test_multiarray.TestFromToFile.test_malformed a few hundred times. It may be
> relevant to note that thread 2 is the GC thread, and thread 1 is the main
> thread. I have considered the following possibilities:
>
> (1) That I'm locking on the wrong object. I believe that isn't the case,
> because it's constructed only once, as a "new Object()" (ie, a reference
> type), and is only subsequently used for locking; and, because it keeps the
> same ipy id throughout.
>
> (2) That Monitor.Enter occasionally allows two different threads to acquire
> the same lock. I consider this extremely unlikely, because... well, how many
> multithreaded .NET apps already exist? If Monitor really were broken, I
> think we'd probably know about it by now.
>
> (3) That calling Flush() on a SyncTextWriter (the type of Console.Out)
> doesn't actually do anything, and the output is somehow wrongly ordered
> (although I can't imagine how this could actually be: if the locking is
> really working, then my console writes are strictly sequential). I don't
> have access to the code, so I have no idea how it's implemented, but even if
> this is the case it doesn't help much with the fundamental problem (the
> synchronisation error which follows).
>
> Apart from the above, I'm out of ideas. Can anyone suggest what I've
> missed?
>
> William
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