Re: Please support Coroutines TS in C++

[Jonathan Wakely <jwakely dot gcc at gmail dot com>]

On 16 October 2017 at 08:25, Ramón García wrote:
> ping

As previously stated, nobody is working on it.

GCC is Free Software, so if you really need ths feature you are free
to add it yourself.


>
> On Thu, Aug 31, 2017 at 11:22 AM, Ramón García <ramon.garcia.f@gmail.com> wrote:
>> (repeated, forgot to reply to mailing list)
>>
>> Xi Ruoyao misses completely the point!
>>
>> The amount of error prone boilerplate code, that the programmer would
>> have to write, is huge. See examples in the excellent presentation
>> "C++ coroutines: a negative overhead abstraction"
>> https://www.slideshare.net/SergeyPlatonov/gor-nishanov-c-coroutines-a-negative-overhead-abstraction
>> Video: https://www.youtube.com/watch?v=_fu0gx-xseY
>>
>> What one can have with a coroutine library, are stackfull coroutines.
>> But they are not really useful. Not very scalable. The simplification
>> of programming has a high cost.
>>
>> With stackless coroutines, one can combine the simplicity of
>> sequential programming, with the scalability and efficiency of
>> asynchronous programming.
>>
>> Did you ever read Linux kernel code? There is a lot of hand written
>> code that tries to achieve a sequence of actions using chained
>> callbacks:
>>
>> void A()
>> {
>>   a1();
>>   when event E1 happens, run B
>> }
>>
>> void B()
>> {
>>   b1();
>>   when event E2 happends, run C
>> }
>>
>> void C()
>> {
>>  c1()
>> }
>>
>> with Coroutines TS this is turned into
>>
>> void A()
>> {
>>   a1();
>>   co_await E1;
>>   b1();
>>   co_await E2;
>>   c1();
>> }
>>
>> but have the same efficiency and scalability of asynchronous code.
>>
>> On Sat, Aug 19, 2017 at 5:49 PM, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
>>> See the thread on gcc-help:
>>> https://gcc.gnu.org/ml/gcc-help/2017-08/msg00045.html
>>>
>>>
>>>
>>> On 19 August 2017 at 14:09, Ramón García <ramon.garcia.f@gmail.com> wrote:
>>>> ping.
>>>>
>>>> On Tue, Aug 15, 2017 at 2:21 PM, Ramón García <ramon.garcia.f@gmail.com> wrote:
>>>>> Hello,
>>>>>
>>>>> Please consider supporting the Coroutines TS in GNU C++.
>>>>>
>>>>> It is really important to make asynchronous programming usable.
>>>>>
>>>>> Modern programs should be scalable to use the performance of multicore
>>>>> processors. Stackless coroutines allow the programmer to scale to
>>>>> millions of asynchronous requests. But without the primitives in the
>>>>> Concurrency TS, chaining the result of an asynchronous computation to
>>>>> the next step, one must program a chain of callbacks. It becomes
>>>>> quickly unusable.
>>>>>
>>>>> The promise/future, as specified in the concurrency TS, (that is, with
>>>>> the function future::then for chaining a callback to the completion of
>>>>> the future) make asynchronous programming somewhat more usable.
>>>>> Unfortunately, almost no C++ library shipped supports future with
>>>>> then.
>>>>>
>>>>> This is an excellent explanation of the Coroutines TS:
>>>>>
>>>>> https://www.slideshare.net/SergeyPlatonov/gor-nishanov-c-coroutines-a-negative-overhead-abstraction
>>>>>
>>>>> Both Visual C++ 2017 and CLANG (SVN version) support the Coroutines
>>>>> TS. Please consider it.
>>>>>
>>>>> I saw that someone started an attempt at implementing it:
>>>>> https://gcc.gnu.org/ml/gcc-patches/2016-03/msg00435.html but there
>>>>> were no replies.