On 22.09.22 21:58, Iain Sandoe wrote:
On 22 Sep 2022, at 13:34, Jonathan Wakely <jwakely.gcc@xxxxxxxxx> wrote:
On Thu, 22 Sept 2022 at 13:29, Wilhelm Meier wrote:
According to the standard, an implementation can avoid the
heap-allocation, if
- the lifetime of the coroutine is strictly within the lifetime of the
caller
- the size of coroutine state can be determined at compile time
Looks like this optimization is not yet available because new/delete-ops
are required.
You can provide your own allocation and deallocation functions in the promise
class :
see - https://eel.is/c++draft/dcl.fct.def.coroutine#9
(and #12).
NOTE: this link is the current C++23 draft, the implementation in GCC follows the
C++20 version (but the basic provision is stil there)
Ok, thank you.
I did that and now it works also on target AVR ;-)
But: the asm-output contains a whole bunch of boilerplate code for
storing the state of the coroutine. So for now I would say it is really
unusable on small targets like AVR.
I think, if the heap operations could be elided away, then the whole
thing should be more efficient.
Regards,
Wilhelm
Is there any work on this topic?
The so-called HALO optimizations are much more difficult than was
originally thought when the wording in the standard was written.
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2477r3.html#background-and-motivation
describes some of the problems.
Agreed, this topic needs more consideration (and it is not mandatory, so should not be relied upon
for the use-case described in any event).
cheers
Iain
Thanks!
Wilhelm
On 21.09.22 15:38, Wilhelm Meier wrote:
I tried to use coroutines with avr-gcc (13.0.0) for the AVR target. I
managed to include the coroutine-header and to write a very simple
generator using the example from cppreference.
It compiles well, but then I get undefined symbols:
1) new and delete operator-functions
2) f(f()::f().Frame*)
Therefore two question arise here:
a) is it possible to use coroutines without head-allocation? E.g. define
some global storage for the state of the coroutine?
b) if a) can be fullfilled, what is 2) supposed to do?
Thanks for any hints,
Wilhelm
