我对如何将
asyncio.Queue
用于特定的生产者-消费者模式感到困惑,其中生产者和消费者同时且独立地运行。
首先,考虑这个示例,它与 asyncio.Queue
import asyncio
import random
import time
async def worker(name, queue):
while True:
sleep_for = await queue.get()
await asyncio.sleep(sleep_for)
queue.task_done()
print(f'{name} has slept for {sleep_for:0.2f} seconds')
async def main(n):
queue = asyncio.Queue()
total_sleep_time = 0
for _ in range(20):
sleep_for = random.uniform(0.05, 1.0)
total_sleep_time += sleep_for
queue.put_nowait(sleep_for)
tasks = []
for i in range(n):
task = asyncio.create_task(worker(f'worker-{i}', queue))
tasks.append(task)
started_at = time.monotonic()
await queue.join()
total_slept_for = time.monotonic() - started_at
for task in tasks:
task.cancel()
# Wait until all worker tasks are cancelled.
await asyncio.gather(*tasks, return_exceptions=True)
print('====')
print(f'3 workers slept in parallel for {total_slept_for:.2f} seconds')
print(f'total expected sleep time: {total_sleep_time:.2f} seconds')
if __name__ == '__main__':
import sys
n = 3 if len(sys.argv) == 1 else sys.argv[1]
asyncio.run(main())
此脚本有一个更详细的细节:项目被同步放入队列中,通过传统的 for 循环
queue.put_nowait(sleep_for)
。
我的目标是创建一个使用
async def worker()
(或 consumer()
)和 async def producer()
的脚本。 两者应安排同时运行。 没有一个消费者协程明确地与生产者绑定或链接。
如何修改上面的程序,使生产者成为自己的协程,可以与消费者/工作人员同时调度?
还有来自 PYMOTW 的第二个示例。 它要求生产者提前知道消费者的数量,并使用
None
作为向消费者发出生产完成的信号。
如何修改上面的程序,使生产者成为自己的协程,可以与消费者/工作人员同时调度?
该示例可以在不改变其基本逻辑的情况下进行推广:
await producer()
或await gather(*producers)
等await queue.join()
处理剩余的项目。这是实现上述内容的示例:
import asyncio, random
async def rnd_sleep(t):
# sleep for T seconds on average
await asyncio.sleep(t * random.random() * 2)
async def producer(queue):
while True:
# produce a token and send it to a consumer
token = random.random()
if token < .05:
break
print(f'produced {token}')
await queue.put(token)
await rnd_sleep(.1)
async def consumer(queue):
while True:
token = await queue.get()
# process the token received from a producer
await rnd_sleep(.3)
queue.task_done()
print(f'consumed {token}')
async def main():
queue = asyncio.Queue()
# fire up the both producers and consumers
producers = [asyncio.create_task(producer(queue))
for _ in range(3)]
consumers = [asyncio.create_task(consumer(queue))
for _ in range(10)]
# with both producers and consumers running, wait for
# the producers to finish
await asyncio.gather(*producers)
print('---- done producing')
# wait for the remaining tasks to be processed
await queue.join()
# cancel the consumers, which are now idle
for c in consumers:
c.cancel()
asyncio.run(main())
请注意,在现实生活中的生产者和消费者中,尤其是涉及网络访问的生产者和消费者中,您可能希望捕获处理过程中发生的与 IO 相关的异常。如果异常是可恢复的,就像大多数与网络相关的异常一样,您可以简单地捕获异常并记录错误。您仍然应该调用
task_done()
,否则 queue.join()
将因未处理的项目而挂起。如果重新尝试处理该项目有意义,您可以在调用 task_done()
之前将其返回到队列中。例如:
# like the above, but handling exceptions during processing:
async def consumer(queue):
while True:
token = await queue.get()
try:
# this uses aiohttp or whatever
await process(token)
except aiohttp.ClientError as e:
print(f"Error processing token {token}: {e}")
# If it makes sense, return the token to the queue to be
# processed again. (You can use a counter to avoid
# processing a faulty token infinitely.)
#await queue.put(token)
queue.task_done()
print(f'consumed {token}')