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我正在试验一下python的asyncio协议。我从官方文档中发现this example,并希望稍微修改它并重现它的beahviour。所以我写了下面两个脚本:Python asyncio简单示例
# 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我得到以下的输出:
$ python3.5 async_test.py
Event loop started
Process created
Getting pipes...
Protocol initialised
Waiting for child to exit...
Data received
而且它只是挂起。
如果我取消了pipe_connection_lost
方法,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
而且仍在进程挂起。我认为发生的是由于某种原因,子进程(get_rand.py
)关闭了管道(如上面的输出所示),但未终止,因此父节点可以从yield from exit_future
开启。我真的不明白这种行为背后的原因,考虑到我的代码大部分都是从python文档中的示例复制粘贴的。
这的确可以解决问题,谢谢! –