[cpp-threads] Asynchronous Function Proposal

[Howard Hinnant]

On Jun 1, 2009, at 2:57 PM, Lawrence Crowl wrote:

> On 6/1/09, Howard Hinnant <hinnant at twcny.rr.com> wrote:
>> I agree with Peter's comments regarding collapsing the number of
>> signatures, though he did a better job of it than I would have.
>> At the very least we don't need:
>>
>> async(fully_threaded policy, F f);
>> async(fully_threaded policy, F&& f, Args&&...);
>>
>> Just one or the other.  The first if you want to go with Herb's
>> suggestion, else just the second.
>>
>> Either by value (F) or by rvalue ref (F&&) will work, but if the
>> latter you probably want to work decay into the effects clause
>> similar to that suggested by:
>>
>> http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#929
>>
>> or
>>
>> http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#817
>>
>> The use of the decay trait enables one to get the "decay behavior"
>> for things like string literals.
>>
>>> Requires: F and each type Ti in Args shall be CopyConstructible if  
>>> an
>>> lvalue and otherwise MoveConstructible.
>>
>> I believe MoveConstructible is sufficient and should be specified
>> with concepts.  The requirements you're trying to specify (how
>> to bind an argument to the parameter) are the caller's concern
>> and not the async function's concern.  But async is going to
>> need to move construct from the host thread's parameter into
>> a bit of memory that the child thread (and future) can access,
>> so needs MoveConstructible there.
>
> For the record, I copied the wording from std::thread construction.
> While I have no strong feeling on the form of passing parameters,
> I think it is important to maintain an interface that is consistent
> with std::thread.
>
> If the above chnage is valuable, can and should we apply it to
> std::thread as well?

Yup.  Still need to conceptify thread...

http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#929 also  
works on the thread ctor (does the decay dance but doesn't do concepts  
yet).

-Howard