Re: [boost] [thread] countdown_latch

Subject: Re: [boost] [thread] countdown_latch
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-05-25 09:26:24

Le 25/05/13 14:45, Gaetano Mendola a écrit :
> On 21/05/2013 07.13, Vicente J. Botet Escriba wrote:
>> Le 20/05/13 22:09, Gaetano Mendola a écrit :
>>> On 27/04/2013 09.05, Vicente J. Botet Escriba wrote:
>>>> Le 22/04/13 10:16, Michael Marcin a écrit :
>>>>> On 4/21/2013 11:30 PM, Vicente J. Botet Escriba wrote:
>>>>>
>>>> Hi,
>>>>> Back on topic of latches and barriers.
>>>>> I was reading up on Java's CyclicBarrier and found its await return
>>>>> value pretty interesting and probably fairly free to implement.
>>>>>
>>>>> "...each invocation of await() returns the arrival index of that
>>>>> thread at the barrier."
>>>>>
>>>>> "the arrival index of the current thread, where index getParties() 
>>>>> - 1
>>>>> indicates the first to arrive and zero indicates the last to arrive."
>>>>>
>>>>> To do this in boost::thread::barrier you would just have to cache
>>>>> m_count right after the decrement and return it instead of the 
>>>>> current
>>>>> true/false.
>>>>>
>>>>>
>>>>
>>>> Yes, boost::barrier return true for the last wait. The change would be
>>>> quite simple, but what would be he utility of such an index?
>>>>
>>>> I have implemented a first prototype of a latch class that could be 
>>>> used
>>>> also as a barrier. I don't know if the name is the good one then.
>>>> I have also implemented a completion_latch class that is able to 
>>>> call a
>>>> function when the counter reaches zero. I'm not satisfied with the
>>>> current implementation as it needs a lot of synchronization.
>>>>
>>>> The change set is https://svn.boost.org/trac/boost/changeset/84055. To
>>>> see the sources, you would need to update the trunk or to take a 
>>>> look at
>>>> https://svn.boost.org/svn/boost/trunk/boost/thread/
>>>>
>>>> Please let me know what do you think.
>>>
>>> What's the plan for this countdown_latch is it candidate to be included
>>> in version 1.54 ?
>>>
>>>
>> No, documentation and tests are missing. I hope it will be ready for
>> 1.55. This and other addition will be experimental and its interface
>> will be subject to some changes.
>> E.g. I have not decided yet how to provide cyclic latches.
>
> Given the fact I have my own implementation of a latch, can you please
> explain what a cyclic latch is, to see if my latch already provide
> the feature. I will propose my implementation of latch.
>
>
boost::barrier resets the counter once all the threads synchronize, so 
that the barrier can be reused again. In order to do that the barrier 
store the initial counter value and reuse it at each cycle.

I don't know if I all the latched must support this feature (possibly by 
a configuration parameter) or if it is better to have a separated 
cyclic_latch.

Best,
Vicente