Re: [boost] [thread] countdown_latch

Subject: Re: [boost] [thread] countdown_latch
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-05-26 03:53:34

Le 25/05/13 15:51, Gaetano Mendola a écrit :
> On 25/05/2013 15.26, Vicente J. Botet Escriba wrote:
>> 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 :
>>>>>
>>>>> 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.
>
> So what are you proposing is a latch that as soon have reached 0 it will
> reset to the initial value and permitting a wait to continue without 
> stopping if it arrives after the reset or to block waiting for a reset.
> My latch doesn't provide such feature, but isn't enough to keep a 
> counter (reset_counter) increased at each reset and decreased at each 
> wait() (before exiting from it). This way the wait shall be a blocking 
> call if the "reset counter" is > 0.
>
> I would make two different names:  latch and cyclic_latch
Thanks for your advice.
The alternative is to have a bool parameter on the constructor and make 
use of a "restore counter" when "reset counter" is > 0 which is not too 
expensive. This needs however to store another integer for the "restore 
counter". I want to be sure that this doesn't adds any additional 
constraint to the class.
>
> I'm also to remove the precondition counter > 0 on the latc::count_down.
>
>
>
I don't see yet the case of a thread using countdown several times the 
same latch as a valid use case. But maybe if you post a concrete (real) 
example, it could make me change.

Best,
Vicente