Messages in this thread | | | Date | Sat, 27 Oct 2007 09:59:07 -0700 (PDT) | From | Davide Libenzi <> | Subject | Re: epoll design problems with common fork/exec patterns |
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On Sat, 27 Oct 2007, Marc Lehmann wrote:
> > Please provide some code to illustrate one exact problem you have. > > // assume there is an open epoll set that listens for events on fd 5 > if (fork () = 0) > { > close (5); > // fd 5 is now removed from the epoll set of the parent. > _exit (0); > }
Hmmm ... what? I assume you know that:
1) A file descriptor is a userspace view/handle of a kernel object
2) The kernel object has a use-count for as many file descriptors that have been handed out to userspace
3) A close() decreases the internal counter by one
4) The kernel object gets effectively closed when the internal counter goes to zero
5) A fork() acts as a dup() on the file descriptors by hence bumping up its internal counter
6) Epoll removes the file from the set, when the *kernel* object gets closed (internal use-count goes to zero)
With that in mind, how can the code snippet above trigger a removal from the epoll set?
- Davide
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