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From Henry Jen <henry...@ztune.net>
Subject Re: Recursive mutex
Date Thu, 21 Jul 2005 18:37:29 GMT
Cliff Woolley wrote:
> 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?
> 

I just looked into SVN at 0.9.4(thanks Joe for pointing me there), 
that's pretty much what I planned to do. The trylock does not seem to be 
right though.

However, I would like to know what's wrong with that implementation and 
try to figure out how it can be fixed.

Cheers,
Henry

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