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by badamp
2495 days ago
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> You do not really await anything. What actually happens is an event handler gets called on an event, So the event handler gets called immediately? No that’s not right. What would be the point of that? The event handler or continuation obviously needs to be scheduled on something that is awaitable. Meanwhile, other concurrent tasks may be able to run. > This is the essence of asynchronous programming. There are no tasks, no yielding, practically no overhead and everything is deterministic This is just totally wrong. Especially re tasks:
https://docs.python.org/3/library/asyncio-task.html#creating... There is nothing inherent about async and await that prevents “yielding”... the issue of yielding and semaphores is a concurrency issue and since async and await are used in concurrent programming environments, the same issues apply. While it is true async and await don’t require any kind of cooperative concurrent framework to work, that is kind of their whole point for existing. A single task async/await system isn’t terribly interesting. |
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It's kind of like this: async/await is syntactic sugar for higher-order abstractions around event loops. At the level of event loops and event hadnlers there is no awaiting anymore. And the whole point of event loops is to not run event handlers concurrently, that's why they are even called loops, they invoke handlers one by one in a loop deterministically without concurrent tasks and once there is nothing more to run they just block and wait for new events. Obviously you can run multiple event loops in parallel, but you shouldn't share memory between them, as it defeats the purpose, is always slower and is never really necessary, you can just use asynchronous message passing to communicate between event loops when you have to.
> A single task async/await system isn’t terribly interesting.
And yet this is the whole point of async/await, promises, futures and event loops. All of them exist to avoid mistakes and performance problems of shared memory concurrency. I mean, really, if you have semaphores or mutexes in event handlers, futures, promises or async functions - you are in a broken concurrency model zone.