9.9. AsyncIO Task¶
asyncio.create_task(coro, *, name=None)
Tasks are used to schedule coroutines concurrently
corocoroutine into a
Taskand schedule its execution
Taskcan be used to cancel execution
Taskcan be awaited until it is complete
The task is executed in the loop returned by
RuntimeErroris raised if there is no running loop in current thread
Tasks are used to run coroutines in event loops
If a coroutine awaits on a Future, the Task suspends the execution of the coroutine and waits for the completion of the Future
When the Future is done, the execution of the wrapped coroutine resumes
Manual instantiation of
Use the high-level
asyncio.create_task()function to create Tasks
Tasks are used to run coroutines in event loops. If a coroutine awaits on a Future, the Task suspends the execution of the coroutine and waits for the completion of the Future. When the Future is done, the execution of the wrapped coroutine resumes.
Event loops use cooperative scheduling: an event loop runs one Task at a time. While a Task awaits for the completion of a Future, the event loop runs other Tasks, callbacks, or performs IO operations.
Use the high-level asyncio.create_task() function to create Tasks, or the low-level loop.create_task() or ensure_future() functions. Manual instantiation of Tasks is discouraged.
>>> import asyncio
>>> async def work(): ... return 'done' >>> >>> >>> async def main(): ... task = asyncio.create_task(work()) ... result = await task ... print(result) >>> >>> >>> asyncio.run(main()) done
>>> async def a(): ... print('a: started') ... await asyncio.sleep(1) ... print('a: finished') ... return 'a' >>> >>> async def b(): ... print('b: started') ... await asyncio.sleep(0.5) ... print('b: finished') ... return 'b' >>> >>> async def c(): ... print('c: started') ... await asyncio.sleep(1.5) ... print('c: finished') ... return 'c' >>> >>> >>> async def main(): ... t1 = asyncio.create_task(a()) ... t2 = asyncio.create_task(b()) ... t3 = asyncio.create_task(c()) ... await t1 ... await t2 ... await t3 >>> >>> >>> asyncio.run(main()) a: started b: started c: started b: finished a: finished c: finished
9.9.4. Selected Task Methods¶
asyncio.Task(coro, *, loop=None, name=None)- A Future-like object that runs a Python coroutine. Not thread-safe.
asyncio.Task.cancel(msg=None)- Request the Task to be cancelled. This arranges for a
CancelledErrorexception to be thrown into the wrapped coroutine on the next cycle of the event loop.
asyncio.Task.result()- Return the result of the
Task. If the result isn't yet available, raise
asyncio.Task.exception()- Return the exception of the
asyncio.Task.add_done_callback(callback, *, context=None)- Add a callback to be run when the
asyncio.Task.remove_done_callback(callback)- Remove callback from the callbacks list.
asyncio.Task.set_name(value)- Set the name of the
asyncio.Task.get_name()- Return the name of the
asyncio.current_task(loop=None)- Return the currently running Task instance, or None if no task is running.
asyncio.all_tasks(loop=None)- Return a set of not yet finished Task objects run by the loop.
If loop is
get_running_loop()is used for getting current loop.