Messages in this thread | | | Date | Mon, 1 Oct 2007 12:04:58 -0700 (PDT) | From | Davide Libenzi <> | Subject | Re: F_DUPFD_CLOEXEC implementation |
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On Mon, 1 Oct 2007, Denys Vlasenko wrote:
> On Monday 01 October 2007 19:16, Al Viro wrote: > > * it's on a bunch of cyclic lists. Have its neighbor > > go away while you are doing all that crap => boom > > * there's that thing call current position... It gets buggered. > > * overwriting it while another task might be in the middle of > > syscall involving it => boom > > Hm, I suspected that it's herecy. Any idea how to do it cleanly? > > > * non-cooperative tasks reading *in* *parallel* from the same > > opened file are going to have a lot more serious problems than agreeing > > on O_NONBLOCK anyway, so I really don't understand what the hell is that for. > > They don't even need to read in parallel, just having shared fd is enough. > Think about pipes, sockets and terminals. A real-world scenario: > > * a process started from shell (interactive or shell script) > * it sets O_NONBLOCK and does a read from fd 0... > * it gets killed (kill -9, whatever) > * shell suddenly has it's fd 0 in O_NONBLOCK mode > * shell and all subsequent commands started from it unexpectedly have > O_NONBLOCKed stdin.
I told you how in the previous email. You cannot use the:
1) set O_NONBLOCK 2) read/write 3) unset O_NONBLOCK
in a racy-free fashion, w/out wrapping it with a lock (thing that we don't want to do).
PS: send/recv are socket functions, and you really don't want to overload them for other fds.
- Davide
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