New submission from Марк Коренберг:
Suppose that program:
====================================
import asyncio
import socket
def receiver(loop):
(a, b) = socket.socketpair()
loop.call_later(1, lambda: print('Should be called inside the loop'))
end = loop.time() + 3
print('Starting busy receiver')
while loop.time() < end:
a.send(b'test')
yield from loop.sock_recv(b, 65536)
# yield from asyncio.sleep(0) # <=====================
print('Busy receiver complete')
# just not to stop ioloop immediatelly
yield from asyncio.sleep(0.5)
def main():
loop = asyncio.get_event_loop()
loop.run_until_complete(receiver(loop))
loop.close()
if __name__ == '__main__':
main()
====================================
Without asyncio.sleep(0) it will not fire time-delayed calls! If I add
asyncio.sleep(0), everything work right. As I think, It is because recv()
syscall is always succeeded, and we never return to ioloop (to epoll() I mean).
In other words, it is classical `reader starvation` as mentioned in "man epoll".
It is not documented, that this function may block event loop, in spite of it
returns coroutine! I thought that this function will setup EPOLLIN event for
socket's FD + call recv() after that. I spent many time to debug program.
----------
components: asyncio
messages: 245952
nosy: gvanrossum, haypo, mmarkk, yselivanov
priority: normal
severity: normal
status: open
title: asyncio.sock_recv() blocks normal ioloop actions.
type: behavior
versions: Python 3.4
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue24532>
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