Function future_add_to_awaited_by

Lib/asyncio/futures.py:428–453

Record that `fut` is awaited on by `waiter`.

(fut, waiter, /)

def future_add_to_awaited_by(fut, waiter, /):
    """Record that `fut` is awaited on by `waiter`."""
    # For the sake of keeping the implementation minimal and assuming
    # that most of asyncio users use the built-in Futures and Tasks
    # (or their subclasses), we only support native Future objects
    # and their subclasses.
    #
    # Longer version: tracking requires storing the caller-callee
    # dependency somewhere. One obvious choice is to store that
    # information right in the future itself in a dedicated attribute.
    # This means that we'd have to require all duck-type compatible
    # futures to implement a specific attribute used by asyncio for
    # the book keeping. Another solution would be to store that in
    # a global dictionary. The downside here is that that would create
    # strong references and any scenario where the "add" call isn't
    # followed by a "discard" call would lead to a memory leak.
    # Using WeakDict would resolve that issue, but would complicate
    # the C code (_asynciomodule.c). The bottom line here is that
    # it's not clear that all this work would be worth the effort.
    #
    # Note that there's an accelerated version of this function
    # shadowing this implementation later in this file.
    if isinstance(fut, _PyFuture) and isinstance(waiter, _PyFuture):
        if fut._Future__asyncio_awaited_by is None:
            fut._Future__asyncio_awaited_by = set()
        fut._Future__asyncio_awaited_by.add(waiter)


def future_discard_from_awaited_by(fut, waiter, /):