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From Cliff Woolley <jwool...@virginia.edu>
Subject Re: Recursive mutex
Date Thu, 21 Jul 2005 18:15:52 GMT
On Thu, 21 Jul 2005, Nick Kew wrote:
> On Wed, 20 Jul 2005, Henry Jen wrote:
>
> > I need to have recursive(NESTED) mutex support in our project.
> >
> > Currently apr is relying on pthread lib to provide
> > pthread_mutexattr_settype to provide recursive support, unfortunately,
> > that does not seem to be in POSIX standard and is not available on the
> > requested linux platform(see
> > http://www.lynuxworks.com/products/posix/function-calls.php3).
> >
> > I plan to implement that in apr by extend current apr_thread_mutex_t to
> > include a pthread_t and an integer for count, and modify the lock/unlock
> > accordingly. So here are couple questions:
> >
> > 1. Is this a reasonable solution or I overlook something? Or maybe
> > someone had done similar?
>
> Looks reasonable to me at first glance.  Bear in mind that anything
> APR exports should be cross-platform, so you'll want to implement it
> in the platform-independent layer.  Unless I'm misunderstanding the
> scope of what you propose.
>
> > 2. How fast can this modification can be rolled into a formal apr
> > release? It is going to be API compatible but not ABI(as the structure
> > changed, only in the case of underlying pthread lib does not support
> > recursive mutex, so should be OK)
>
> That's likely to be a while: it'll need to get reviewed, agreed on,
> and then used in a test version for a while, then await sufficient
> general agreement for a release incorporating it.

I have this vague recollection that we specifically excluded recursive
mutexes from the API at some point in the past because there were deadlock
problems that made it impossible to implement this portably.  Perhaps
Justin or Aaron remembers more details?

--Cliff

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