pythonasynchronouspython-asyncio

Will functions run twice with asyncio.gather(create_task(task))

What will be happened, if I run:

tasks = []
for item in items:
  tasks.append(asyncio.create_task(f(item)))

res = asyncio.gather(*tasks)

Will functions run twice? After create_task and after gather

Solution

  • First, note that you must await asyncio.gather() for them to actually wait for them to finish.

    Once that is fixed, the functions will run only once. create_task() submits them to the event loop. After that, they will run during the next await. asyncio.gather() simply waits until they are done. For example, this will run them in two phases:

    tasks = []
for item in items:
  tasks.append(asyncio.create_task(f(item)))

await asyncio.sleep(1)   # here they start running and run for a second
res = await asyncio.gather(*tasks)  # here we wait for them to complete