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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：
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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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