CODEWITHSUNDEEP
pythonpython-asyncio
user1008636
user1008636

Reputation: 3211

Why use async.gather in Python?

Let's say we have

await async_function_one_with_large_IO_request()
await async_function_two_with_large_IO_request()

versus

asyncio.gather(
  async_function_one_with_large_IO_request(), 
  async_function_two_with_large_IO_request())

In the first version, once we hit the 'large io request' part of function one, it's gonna move onto running function_two, that's the whole point of await, right?

Isn't that what version 2 with gather does too?

What's the performance difference between the two?

Upvotes: 0

Views: 314

Answers (1)

larsks
larsks

Reputation: 312690

In the first version, once we hit the 'large io request' part of function one, it's gonna move onto running function_two, that's the whole point of await, right?

That's incorrect. In your first version, async_function_two_with_large_IO_request (which I will call function_two) won't run until async_function_one_with_large_IO_request (which I will call function_one) completes.

If function_one happens to await on another function, it will yield control to another running async task, but function_two hasn't been scheduled yet.

When you use asyncio.gather, the tasks are scheduled concurrently, so if function_one awaits on something, function_two has a chance to run (along with other async tasks).

Note that asyncio.gather creates an async task, which generally implies you have to await on it:

await asyncio.gather(...)

The Python documentation covers this in detail in Coroutines and Tasks.

Upvotes: 1

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