Re: [boost] [chrono] [thread] boost.chrono changes to boost::condition_variables

Subject: Re: [boost] [chrono] [thread] boost.chrono changes to boost::condition_variables
From: Howard Hinnant (howard.hinnant_at_[hidden])
Date: 2010-07-26 09:05:17

On Jul 26, 2010, at 8:48 AM, Morgan wrote:

>> Templating the condition_variable on clock_type was specifically avoided for
>> std::condition_variable because a condition_variable often has more than one 
>> waiting client at a time, and it was felt that those different waiting 
>> clients should be able to use different clocks simultaneously when waiting 
>> on a (absolute) time_point. 
> 
> Of course; you are correct.  
> 
> I was being misled by the existing pthread implementation of 
> boost::condition_variables and boost::chrono which currently enforces a single
> clock on all clients of a condvar.
> 
> This limitation seems to have been inherited from pthread_cond_timedwait and 
> pthread_cond_init which do not provide the fexibility for mixing of clock types 
> for waiting clients of a cv.  (The pthread_cond clock type is fixed at condvar 
> creation).  
> 
> Fixing this limitation would now seem to be a problem for the pthread platform 
> implementation, rather than the boost API and the standard.
> 
> I'll propose some changes to boost::chrono pthread implementation in line with
> the draft standard.

There's more info on this topic here:

http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#887

-Howard