[omniORB] Deadlock on recursive invocation with SINGLE_THREAD_MODEL

[Michael]

Felix Nawothnig wrote:
>> omniORB behaves correctly.
> 
> Well, I didn't really claim otherwise... but given the choice between an
> operation deadlocking and not deadlocking I don't quite see the benefit of
> the former.
> 
>> ...and the developers think: Avoid SINGLE_THREAD_MODEL, use locks to
>> serialize your objects.
> 
> When dealing with inherently single-threaded software components that's
> hardly sensible. Ignoring the obviously unnecessary boilerplate code (and
> lots of places to forget the lock...) for the sake of argument - putting
> one giant lock around everything doesn't help avoiding the
> recursive-invokation deadlock at all...
> 
> Yes, one could use a recursive mutex... not very nice though.
> 
> And all that doesn't help when you're dealing with software which expects
> (and verifies) that it's being accessed from a single thread. Note that
> I'm using such software - and it's not some obscure arcane proprietary
> crap but just Qt.
> 
> Now you need to marshal every request, along with it's parameters into
> that thread and back. That will obviously result in about the same amount
> of hand-written boilerplate code as generated by the IDL compiler, after
> all you are doing nearly the same thing.
> 
> I worked on a project where developers did exactly that (for no apparent
> reason though, in their case there was no thread-safety needed .. nor
> gained).
> 
> About a year after I ripped out the code in question (about 50k lines of
> fabulous copy&paste-work) I can laugh about it, but when you have to deal
> with code like that it hurts.
> 
> Badly.
> 
> So _please_ don't tell me do this. ;-)
> 
> So, no, SINGLE_THREAD_MODEL does not need to be feared. It has some real
> world uses. And my book says this is _exactly_ what it is there for.
> 
> Cheers,
> 
> Felix
> 
> 

No doubt there has been a reason why this policy is in the standard. All
I wanted to say is that usually it causes lots of trouble (which is not
CORBA related but just based on the fact that it is single threaded). If
I remember correctly omniORB implements single_threaded through locking
anyway (but maybe Duncan would be more competent to answer that).

You could also implent locking in interceptors, much less copy and paste
 in that case.

And yes, sometimes things are painful :)