I am new to the asyncio subject, just trying to figure out how to use it. Below
is the script I use for testing:
---------------------------------
# asyncio_cancel_task2.py
import asyncio
@asyncio.coroutine
def task_func():
print('in task_func, sleeping')
try:
yield from asyncio.sleep(1)
except asyncio.CancelledError:
print('task_func was canceled')
raise
print('return result')
return 'the result'
def task_canceller(task):
task.cancel()
print('canceled the task')
@asyncio.coroutine
def main(loop):
print('first, scheduling a task')
task = loop.create_task(task_func())
print('second, scheduling its cancellation')
loop.call_later(0.5, task_canceller, task)
try:
print('waiting task to complete')
yield from task
except asyncio.CancelledError:
print('main() also sees task as canceled')
event_loop = asyncio.get_event_loop()
try:
event_loop.run_until_complete(main(event_loop))
finally:
print('wait 3 seconds before closing event_loop')
asyncio.sleep(3)
print('event_loop was closed')
event_loop.close()
-----------------------------------
It schedules two tasks, the task_func and the task_canceller, in main. Before
the task_func completed, the task_canceller was fired to cancel it. Hence its
output below seems reasonable.
D:\Works\Python>py
Python 3.4.4 (v3.4.4:737efcadf5a6, Dec 20 2015, 19:28:18) [MSC v.1600 32 bit
(Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import asyncio_cancel_task2
first, scheduling a task
second, scheduling its cancellation
waiting task to complete
in task_func, sleeping
canceled the task
task_func was canceled
main() also sees task as canceled
wait 3 seconds before closing event_loop
event_loop was closed
>>>
Then, I changed the call_later delay from 0.5 to 1.5, expect it to be called
after the task_func completed and before the event loop closed. The output
seems not quite right. Why the task_canceller hasn't been called?
>>> import asyncio_cancel_task2
first, scheduling a task
second, scheduling its cancellation
waiting task to complete
in task_func, sleeping
return result
wait 3 seconds before closing event_loop
event_loop was closed
>>>
Best Regards,
Jach Fong
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