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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