On 25 Feb 2021, at 17:15, Jonathan Slenders <jonathan@slenders.be> wrote:

It does make sense to have a barrier synchronization primitive for asyncio.

The idea is to make a coroutine block until at least X coroutines are waiting to enter the barrier.

This is very useful, if certain actions need to be synchronized.

Recently, I had to implement a barier myself for our use case. See code below:

It is simple to implement, but I too would like to have one for asyncio, in order to be consistent with the concurrency primitives we have for threading.

Jonathan

class Barier:
    """
    Make a coroutine block until there are at least X waiters.

    Similar to the threading Barier objects but for asyncio:
    https://docs.python.org/3/library/threading.html#barrier-objects
    """

    def __init__(self, parties: int) -> None:
        self.parties = parties
        self._waiting: int
        self._event = asyncio.Event()

    def add_one(self) -> None:
        self._waiting += 1
        if self._waiting == self.parties:
            self._event.set()

    async def wait(self, worker: "Worker") -> None:
        """
        Wait until all we have at least `parties` waiters.
        """
        self.add_one()
        await self._event.wait()

Le jeu. 25 févr. 2021 à 16:42, Barry Scott <barry@barrys-emacs.org> a écrit :

> On 25 Feb 2021, at 13:14, Yves Duprat <yduprat@gmail.com> wrote:
>
> Hi,the list,
>
> I'm wondering why Barrier object does not exist in the synchronization primitives of the asyncio lib while it is present in threading and multiprocessing libs ?
> This may not be the right place to ask this question, but I never found an answer on the web.
> Thanks for your help.


I'm assuming that the barrier you are speaking of is the mechanism that is used to
synchronise threads/processes running in parallel to prevent data races.

With async code that is never an issue. Each function runs to completion uninterrupted.
There are no data races. Each time a async function runs it can know that the state of
the objects it uses will not be changed while it is running.

Barry



>
> Yves
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