_io_epoll.py 文件源码

def flags(self):
        flags = 0
        if self.read_task is not None:
            flags |= select.EPOLLIN
        if self.write_task is not None:
            flags |= select.EPOLLOUT
        if not flags:
            return None
        # XX not sure if EPOLLEXCLUSIVE is actually safe... I think
        # probably we should use it here unconditionally, but:
        # https://stackoverflow.com/questions/41582560/how-does-epolls-epollexclusive-mode-interact-with-level-triggering
        #flags |= select.EPOLLEXCLUSIVE
        # We used to use ONESHOT here also, but it turns out that it's
        # confusing/complicated: you can't use ONESHOT+EPOLLEXCLUSIVE
        # together, you ONESHOT doesn't delete the registration but just
        # "disables" it so you re-enable with CTL rather than ADD (or
        # something?)...
        # https://lkml.org/lkml/2016/2/4/541
        return flags