Re: [boost] [thread] Are thread ids unique during an applicationslife time?

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2008-05-28 17:58:38

On May 28, 2008, at 3:02 PM, Peter Dimov wrote:

> Howard Hinnant:
>
>> I've used this (for example) in implementing recursive mutexes:
>>
>> class recursive_mutex
>> {
>>   unsigned state_;
>>   std::thread::id id_;
>
> As already pointed out in the thread
>
> http://www.decadentplace.org.uk/pipermail/cpp-threads/2006-August/001091.html
>
> linked from #783, this requires thread::id atomicity, which is not
> guaranteed. I'm not sure whether instant reuse can also break this
> particular example, but it definitely breaks other uses of thread::id.

I probably made a mistake in posting code snippets instead of a  
complete recursive_mutex.  In the example I programmed, which was  
actually a recurisve_timed_mutex instead of a recursive_mutex, there  
were member mutex and condition_variables.  The mutex was locked while  
manipulating the internal state_ and id_, providing the required  
atomicity, and preventing "instant reuse".

Since "not a thread" values do not exist (as far as I know) in  
pthreads and Windows, I was trying to make the point that many people  
probably haven't considered the use of such values in multithreading  
programming in dealing with the id-reuse-problem.  I believe this tool  
will solve some, but not all, problems which "unique_id" addresses,  
and with far less expense.

-Howard