python 使用事件对象asyncio.Event来同步协程的操作
(编辑：jimmy 日期: 2024/11/18 浏览：3 次 )
事件对象asyncio.Event是基于threading.Event来实现的。
事件可以一个信号触发多个协程同步工作，
例子如下：
import asyncio
import functools
def set_event(event):
print('setting event in callback')
event.set()
async def coro1(event):
print('coro1 waiting for event')
await event.wait()
print('coro1 triggered')
async def coro2(event):
print('coro2 waiting for event')
await event.wait()
print('coro2 triggered')
async def main(loop):
# Create a shared event
event = asyncio.Event()
print('event start state: {}'.format(event.is_set()))
loop.call_later(
0.1, functools.partial(set_event, event)
)
await asyncio.wait([coro1(event), coro2(event)])
print('event end state: {}'.format(event.is_set()))
event_loop = asyncio.get_event_loop()
try:
event_loop.run_until_complete(main(event_loop))
finally:
event_loop.close()
输出如下：
event start state: False coro2 waiting for event coro1 waiting for event setting event in callback coro2 triggered coro1 triggered event end state: True
补充知识： python里使用协程来创建echo客户端
在这个例子里使用asyncio.Protocol来创建一个echo客户端，先导入库asyncio和logging。
接着定义发送的消息MESSAGES。
创建连接服务器的地址SERVER_ADDRESS，接着创建EchoClient类，它是继承asyncio.Protocol。
在这个类的构造函数里，接收两个参数messages和future，
messages是指定要发送的消息数据，future是用来通知socket接收数据完成或者服务器关闭socket的事件通知，以便事件循环知道这个协程已经完成了，就可以退出整个程序。
connection_made函数是当socket连接到服务器时调用，它就立即发送数据给服务器，数据发送完成之后发送了eof标记。
服务器收到数据和标志都回复客户端，客户端data_received函数接收数据，eof_received函数接收结束标记。
connection_lost函数收到服务器断开连接。
这行代码：
client_completed = asyncio.Future()
创建一个协程完成的触发事件。
由于event_loop.create_connection函数只能接收一个参数，需要使用functools.partial来进行多个参数包装成一个参数。
后面通过事件循环来运行协程。
import asyncio
import functools
import logging
import sys
MESSAGES = [
b'This is the message. ',
b'It will be sent ',
b'in parts.',
]
SERVER_ADDRESS = ('localhost', 10000)
class EchoClient(asyncio.Protocol):
def __init__(self, messages, future):
super().__init__()
self.messages = messages
self.log = logging.getLogger('EchoClient')
self.f = future
def connection_made(self, transport):
self.transport = transport
self.address = transport.get_extra_info('peername')
self.log.debug(
'connecting to {} port {}'.format(*self.address)
)
# This could be transport.writelines() except that
# would make it harder to show each part of the message
# being sent.
for msg in self.messages:
transport.write(msg)
self.log.debug('sending {!r}'.format(msg))
if transport.can_write_eof():
transport.write_eof()
def data_received(self, data):
self.log.debug('received {!r}'.format(data))
def eof_received(self):
self.log.debug('received EOF')
self.transport.close()
if not self.f.done():
self.f.set_result(True)
def connection_lost(self, exc):
self.log.debug('server closed connection')
self.transport.close()
if not self.f.done():
self.f.set_result(True)
super().connection_lost(exc)
logging.basicConfig(
level=logging.DEBUG,
format='%(name)s: %(message)s',
stream=sys.stderr,
)
log = logging.getLogger('main')
event_loop = asyncio.get_event_loop()
client_completed = asyncio.Future()
client_factory = functools.partial(
EchoClient,
messages=MESSAGES,
future=client_completed,
)
factory_coroutine = event_loop.create_connection(
client_factory,
*SERVER_ADDRESS,
)
log.debug('waiting for client to complete')
try:
event_loop.run_until_complete(factory_coroutine)
event_loop.run_until_complete(client_completed)
finally:
log.debug('closing event loop')
event_loop.close()
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