python協程實時輸出_在python裡協程使用同步鎖Lock的執行個體

盡管asyncio庫是使用單線程來實作協程的，但是它還是并發的，亂序執行的。可以說是單線程的排程系統，并且由于執行時有延時或者I/O中斷等因素，每個協程如果同步時，還是得使用一些同步對象來實作。

比如asyncio就定義了一個鎖對象Lock，它一次隻允許一個協程來通路共享的資源，如果多協程想通路就會阻塞起來，也就是說如果一個協程沒有釋放這個鎖，别的協程是沒有辦法通路共享的資源。

例子：

import asyncio

import functools

def unlock(lock):

print('callback releasing lock')

lock.release()

async def coro1(lock):

print('coro1 waiting for the lock')

with await lock:

print('coro1 acquired lock')

print('coro1 released lock')

async def coro2(lock):

print('coro2 waiting for the lock')

await lock

try:

print('coro2 acquired lock')

finally:

print('coro2 released lock')

lock.release()

async def main(loop):

# Create and acquire a shared lock.

lock = asyncio.Lock()

print('acquiring the lock before starting coroutines')

await lock.acquire()

print('lock acquired: {}'.format(lock.locked()))

# Schedule a callback to unlock the lock.

loop.call_later(0.1, functools.partial(unlock, lock))

# Run the coroutines that want to use the lock.

print('waiting for coroutines')

await asyncio.wait([coro1(lock), coro2(lock)]),

event_loop = asyncio.get_event_loop()

try:

event_loop.run_until_complete(main(event_loop))

finally:

event_loop.close()

輸出結果如下：

acquiring the lock before starting coroutines

lock acquired: True

waiting for coroutines

coro1 waiting for the lock

coro2 waiting for the lock

callback releasing lock

coro1 acquired lock

coro1 released lock

coro2 acquired lock

coro2 released lock

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