Re: [boost] Boost.Threads, N2178, N2184, et al

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2007-03-27 10:02:54

On Mar 27, 2007, at 9:45 AM, Peter Dimov wrote:

> Howard Hinnant wrote:
>
> [ detach vs join ]
>
>> This is a departure from pthread semantics that I am uncomfortable
>> with.  If I accidently get myself into this kind of race.  I think  
>> I'd
>> prefer some noise (an assert, or exception, or crash).
>
> I'm not entirely sure what is the purpose of detach as it's unique  
> to N2184,
> but if it's only used to indicate "do not cancel on ~thread,  
> please", there
> is no need for it to actually detach anything (invalidate the  
> pthread_t
> handle), just set a "don't cancel" flag. The race you describe is then
> harmless.

The purpose of detach is to model the semantics of pthread_detach.   
pthread_detach is described as:

The pthread_detach() function is used to indicate to the  
implementation that storage for the thread thread can be reclaimed  
when that thread terminates. If thread has not terminated,  
pthread_detach() will not cause it to terminate. The effect of  
multiple pthread_detach() calls on the same target thread is  
unspecified.

I am exploring tightening up those semantics up just a bit with  
Anthony's:

> t.detach()    t.detach()    harmless race. Thread is detached.  
> second detach
>                            is no-op.

(watch out for the inevitable, unintentional text wrapping)

-Howard