我正在尝试使用python的asyncio Protocols。我从官方文档中找到了this example，并想稍微修改它并重现它的beahviour。所以我写了以下两个脚本：
# file: get_rand.py
from random import choice
from time import sleep
def main():
print(choice('abcdefghijklmnopqrstuvwxyz'))
sleep(2)
if __name__ == '__main__':
main()
和
# file: async_test.py
import asyncio
class Protocol(asyncio.SubprocessProtocol):
def __init__(self, exit_future):
self.exit_future = exit_future
self.output = bytearray()
print('Protocol initialised')
def pipe_data_received(self, fd, data):
print('Data received')
self.output.extend(data)
#def pipe_connection_lost(self, fd, exc):
# print('Pipe connection lost for the following reason:')
# print(exc)
def subprocess_exited(self):
print('Subprocess exited')
self.exit_future.set_result(True)
@asyncio.coroutine
def get_rand(loop):
exit_future = asyncio.Future(loop=loop)
print('Process created')
created = loop.subprocess_exec(lambda: Protocol(exit_future),
'python3.5', 'get_rand.py',
stdin=None, stderr=None)
print('Getting pipes...')
transport, protocol = yield from created
print('Waiting for child to exit...')
yield from exit_future
transport.close()
print('Gathering data...')
data = bytes(protocol.output)
print('Returning data...')
return data.decode('ascii').rstrip()
def main():
loop = asyncio.get_event_loop()
print('Event loop started')
data = loop.run_until_complete(get_rand(loop))
print('Event loop ended')
print(data)
loop.close()
if __name__ == '__main__':
main()
当我运行async_test.py时，我得到以下输出：
$ python3.5 async_test.py
Event loop started
Process created
Getting pipes...
Protocol initialised
Waiting for child to exit...
Data received
它只是挂起。
如果我取消注释pipe_connection_lost方法，则输出如下：
$ python3.5 async_test.py
Event loop started
Process created
Getting pipes...
Protocol initialised
Waiting for child to exit...
Data received
Pipe connection lost for the following reason:
None
然而这个过程仍然悬而未决。我认为正在发生的是由于某种原因，子进程（get_rand.py）关闭了管道（如上面的输出中所示），但没有终止，以便父进程可以从yield from exit_future解除阻塞。我真的不明白这种行为背后的原因，因为我的代码主要是从python文档中的一个例子中复制粘贴的。