RFC: LLVM Coroutine Representation, Round 2

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1

Hi, Antoine:

Say I have (Python notation):

def coroutine(n):
    for i in range(n):
        yield i

def consumer(n):
    for val in coroutine(n):
        # do something with val

How does consumer() know the coroutine has exited after the n'th
iteration? It can't call @coro.done() as there is a single suspend
point...

There is a single suspend point at a python level, but not, necessarily, at LLVM
level. I would inject two more suspend points in your python frontend, so the
LLVM looks like this:

  Iterator coroutine(int n) {
    int current_value;
    CORO_BEGIN(..., &current_value); // designate current_value as promise
    SUSPEND(); // coroutine starts suspended
    for (int i = 0; i < n; ++i) {
      curren_value = i; SUSPEND(); // yield i
    }
    SUSPEND(/*final=*/true);
    ...
  }

  int __next__(void* hdl) {
    coro.resume(hdl);
    if (coro.done(hdl)) throw StopIteration();
    return *(int*)coro.promise(hdl);
  }

Essentially, for every generator, you always insert an initial suspend point
before any user authored code and you insert a final suspend point after all
the user authored code.

Gor

2

I see, thanks. Perhaps that would be worth mentioning in the document?

Regards

Antoine.