Re: [ECOS] reentrant mutex

[Jonathan Larmour <jifl at eCosCentric dot com>]

Nick Garnett wrote:
> Jonathan Larmour <jifl at eCosCentric dot com> writes:
>
>
> > Nick Garnett wrote:
> >
> > > I would personally not like to see such a patch. It would not work
> > > very well with condition variables and any system that mixed regular
> > > and recursive mutexes would be very hard to debug.
> >
> > I'm not sure it would make that much difference since they would be
> > completely different types... I would agree that making a Cyg_Mutex
> > have configurable behaviour would be bad and confusing. Similarly
> > therefore, since condvars only take a Cyg_Mutex and not a
> > Cyg_Recursive_Mutex (or whatever), it should be fine.
>
>
> Mutexes without condition variables are not very useful. The two are
> complimentary parts of a single synchronization mechanism. Taking the
> patch idea to its logical conclusion, we would also need a set of
> condition variables that took a recursive mutex. We would end up with
> two independent parallel synchonization domains. That would be a
> really nasty can of worms to open.

What, like cnt_sem and cnt_sem2 (or even bin_sem for that matter since 
that isn't in the kapi) ;-). Ditto mboxt and mboxt2.

I don't think having two (semantically different and differently named) 
primitives is a problem. The two cond vars could even share code easily 
enough, so it wouldn't cause any significant maintenance issue.

> > Anyway, I just want to be sure that defining a recursive mutex as a
> > completely different type would still not be acceptable.
>
> I suspect that the only way of doing it is to add a runtime option to
> the mutex implementation to support recursion. However this would
> require some of the API to change and would need an
> up-to-the-elbows-in-blood-and-guts rewrite of the mutex and condition
> variable code, as well as lots of other bits of eCos. The degree of
> instability this would introduce is probably not worth it for a
> relatively minor change in external functionality.

I agree. If it should be done at all, it should be with a separate type.

Jifl
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