Re: For which gcc release is going to be foreseen the support for the Coroutines TS extension?

[Richard Biener <richard.guenther@gmail.com>]

On August 20, 2019 5:19:33 PM GMT+02:00, Nathan Sidwell <nathan@acm.org> wrote:
>On 7/26/19 6:03 AM, Iain Sandoe wrote:
>> Hello Sebastian,
>> 
>>> On 26 Jul 2019, at 10:19, Florian Weimer <fweimer@redhat.com> wrote:
>
>>> C++ coroutines are stackless.  I don't think any new low-level
>run-time
>>> support will be needed.
>> 
>> correct, C++20 coroutines and threading mechanisms are orthogonal
>> facilities; one can use (IS C++20) coroutines on top of a threaded
>system
>> or in a single-threaded environment.
>> 
>> Two places I see them as being a go-to facility in embedded systems
>are:
>>   * co-operative multi-tasking UIs on single-threaded platforms.
>>   * async I/O completion by continuations, rather than callbacks.
>
>There are cases where the overhead of threads is too expensive.  For 
>instance hiding (cache-missing) load latencies by doing other work
>while 
>waiting -- a context switch at that point is far too expensive.

But are coroutines so much lower latency (and a context switch does not involve cache misses on its own?). For doing useful work in this context CPU designers invented SMT... 

Richard. 

>nathan