python中利用队列asyncio.Queue进行通讯详解

前言

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asyncio.Queue与其它队列是一样的，都是先进先出，它是为协程定义的

例子如下：

import asyncio 

async def consumer(n, q):
 print('consumer {}: starting'.format(n))
 while True:
  print('consumer {}: waiting for item'.format(n))
  item = await q.get()
  print('consumer {}: has item {}'.format(n, item))
  if item is None:
   # None is the signal to stop.
   q.task_done()
   break
  else:
   await asyncio.sleep(0.01 * item)
   q.task_done()
 print('consumer {}: ending'.format(n)) 

async def producer(q, num_workers):
 print('producer: starting')
 # Add some numbers to the queue to simulate jobs
 for i in range(num_workers * 3):
  await q.put(i)
  print('producer: added task {} to the queue'.format(i))
 # Add None entries in the queue
 # to signal the consumers to exit
 print('producer: adding stop signals to the queue')
 for i in range(num_workers):
  await q.put(None)
 print('producer: waiting for queue to empty')
 await q.join()
 print('producer: ending') 

async def main(loop, num_consumers):
 # Create the queue with a fixed size so the producer
 # will block until the consumers pull some items out.
 q = asyncio.Queue(maxsize=num_consumers) 

 # Scheduled the consumer tasks.
 consumers = [
  loop.create_task(consumer(i, q))
  for i in range(num_consumers)
 ] 

 # Schedule the producer task.
 prod = loop.create_task(producer(q, num_consumers)) 

 # Wait for all of the coroutines to finish.
 await asyncio.wait(consumers + [prod]) 

event_loop = asyncio.get_event_loop()
try:
 event_loop.run_until_complete(main(event_loop, 2))
finally:
 event_loop.close() 

输出如下：

consumer 0: starting
consumer 0: waiting for item
consumer 1: starting
consumer 1: waiting for item
producer: starting
producer: added task 0 to the queue
producer: added task 1 to the queue
consumer 0: has item 0
consumer 1: has item 1
producer: added task 2 to the queue
producer: added task 3 to the queue
consumer 0: waiting for item
consumer 0: has item 2
producer: added task 4 to the queue
consumer 1: waiting for item
consumer 1: has item 3
producer: added task 5 to the queue
producer: adding stop signals to the queue
consumer 0: waiting for item
consumer 0: has item 4
consumer 1: waiting for item
consumer 1: has item 5
producer: waiting for queue to empty
consumer 0: waiting for item
consumer 0: has item None
consumer 0: ending
consumer 1: waiting for item
consumer 1: has item None
consumer 1: ending
producer: ending

总结

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