同步等待異步協同程序

如果一個異步事件循環已經通過調用loop.run_forever運行，它將阻塞執行線程，直到loop.stop被調用[請參閱docs]。因此，同步等待的唯一方法是在一個專用線程上運行事件循環，在循環上調度異步函數，然后從另一個線程同步地等待它。在

為此，我按照用戶4815162342的answer編寫了自己的最小解決方案。我還添加了在所有工作完成后清理循環的部分[參見^{}]。在

下面代碼中的main函數在一個專用線程上運行事件循環，調度事件循環上的多個任務，以及同步等待結果的任務。同步等待將阻塞，直到所需的結果準備就緒。最后，循環被關閉，并優雅地與其線程一起清理。在

專用線程和函數stop_loop、run_forever_safe、和{}可以封裝在模塊或類中。在

有關線程安全的注意事項，請參閱asyncio docs中的“Concurrency and Multithreading”部分。在import asyncio

import threading

#

def stop_loop(loop):

''' stops an event loop '''

loop.stop()

print (".: LOOP STOPPED:", loop.is_running())

def run_forever_safe(loop):

''' run a loop for ever and clean up after being stopped '''

loop.run_forever()

# NOTE: loop.run_forever returns after calling loop.stop

# cancell all tasks and close the loop gracefully

print(".: CLOSING LOOP...")

# source:

loop_tasks_all = asyncio.Task.all_tasks(loop=loop)

for task in loop_tasks_all: task.cancel()

# NOTE: `cancel` does not guarantee that the Task will be cancelled

for task in loop_tasks_all:

if not (task.done() or task.cancelled()):

try:

# wait for task cancellations

loop.run_until_complete(task)

except asyncio.CancelledError: pass

#END for

print(".: ALL TASKS CANCELLED.")

loop.close()

print(".: LOOP CLOSED:", loop.is_closed())

def await_sync(task):

''' synchronously waits for a task '''

while not task.done(): pass

print(".: AWAITED TASK DONE")

return task.result()

#

async def asyncTask(loop, k):

''' asynchronous task '''

print(" start async task %s" % k)

await asyncio.sleep(3, loop=loop)

print(" end async task %s." % k)

key = "KEY#%s" % k

return key

def main():

loop = asyncio.new_event_loop() # construct a new event loop

# closures for running and stopping the event-loop

run_loop_forever = lambda: run_forever_safe(loop)

close_loop_safe = lambda: loop.call_soon_threadsafe(stop_loop, loop)

# make dedicated thread for running the event loop

thread = threading.Thread(target=run_loop_forever)

# add some tasks along with my particular task

myTask = asyncio.run_coroutine_threadsafe(asyncTask(loop, 100200300), loop=loop)

otherTasks = [asyncio.run_coroutine_threadsafe(asyncTask(loop, i), loop=loop)

for i in range(1, 10)]

# begin the thread to run the event-loop

print(".: EVENT-LOOP THREAD START")

thread.start()

# _synchronously_ wait for the result of my task

result = await_sync(myTask) # blocks until task is done

print("* final result of my task:", result)

#... do lots of work ...

print("*** ALL WORK DONE ***")

#========================================

# close the loop gracefully when everything is finished

close_loop_safe()

thread.join()

#

main()

總結

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