Messages in this thread | | | Date | Fri, 18 Jan 2008 14:43:18 +0100 | From | Pierre Habouzit <> | Subject | epoll and shared fd's |
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Hi,
I just came across a strange behavior of epoll that seems to contradict the documentation. Here is what happens:
* I have two processes P1 and P2, P1 accept()s connections, and send the resulting file descriptors to P2 through a unix socket.
* P2 registers the received socket in his epollfd.
[time passes]
* P2 is done with the socket and closes it
* P2 gets events for the socket again !
Though the documentation says that if a process closes a file descriptor, it gets unregistered. And yes I'm sure that P2 doens't dup() the file descriptor. Though (because of a bug) it was still open in P1[0], hence the referenced socket still live at the kernel level.
Of course the userland workaround is to force the EPOLL_CTL_DEL before the close, which I now do, but costs me a syscall where I wanted to spare one :|
I _believe_ this is if not a bug, at least a misfeature, hence I'm reporting the issue :)
PS: please Cc: on answers me I'm not subscribed.
[0] and despite the bug in our software that leaked the socket, P1 is supposed to only close the socket when P2 acks the fact that it received a valid fd (else P1 tries to send it to a P2'), and there may be uncontrollable races that could trigger the issue again (with P2 closing the socket before P1 had time to process the ACK and close the socket on its end). -- ·O· Pierre Habouzit ··O madcoder@debian.org OOO http://www.madism.org [unhandled content-type:application/pgp-signature] | |