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

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2007-03-25 14:26:59

On Mar 25, 2007, at 12:03 AM, Emil Dotchevski wrote:

> On Windows, you can have two joins on the same thread. Copyable  
> thread handles can support this behavior directly. How does one  
> achieve the same thing with N2184::thread semantics?

You put a N2184::thread on the heap, with a condition variable, mutex  
and reference count accompanying it.  You then create a copyable  
handle to this struct which manages the lifetime with the reference  
count, and access to the thread (and other state such as whether the  
thread as ended or not).  It might look a lot like:

    http://braddock.com/~braddock/future/

which is currently being discussed in the boost thread titled  
"[futures] untyped_promise or future<void>".  As I understand it, this  
copyable, mutli-join handle is currently implemented on top of (or  
perhaps "usable with" is a more accurate statement than "implemented  
on to of") the non-copyable boost::thread.

I do not propose that everyone who needs this functionality go out and  
write their own future.  Instead I propose that std::future (actually  
I like the name std::shared_future) be standardized *in addition to*  
the N2184::thread.  The LWG has looked at futures and is currently  
thinking that TR2 would be a more appropriate target for this  
functionality.

-Howard