Eli Barzilay <eli@barzilay.org> writes:
> [This is a second post, since I didn't get any replies the first time.
> It looks more like a bug now, which sounds strange for something that
> common...]
>
> When I run the following program, and block the terminal's output
> (C-s), the `select' doesn't seem to have any effect, resulting in a
> 100% cpu usage (this is on a RH8, with 2.4.18). I wouldn't be
> surprised if I'm doing something stupid, but it does seem to work fine
> on Solaris.
>
> Is there anything wrong with this, or is this some bug?
>
> ======================================================================
> #include <unistd.h>
> #include <fcntl.h>
> int main() {
> int flags, fd, len; fd_set writefds;
> fd = 1;
> flags = fcntl(fd, F_GETFL, 0);
> fcntl(fd, F_SETFL, flags | O_NONBLOCK);
> while (1) {
> FD_ZERO(&writefds);
> FD_SET(fd, &writefds);
> len = select(fd + 1, NULL, &writefds, NULL, NULL);
> if (!FD_ISSET(fd,&writefds)) exit(0);
> len = write(fd, "hi\n", 3);
> }
> fcntl(fd, F_SETFL, flags);
> }
> ======================================================================
Looks like a bug to me.
Strace says:
select(2, NULL, [1], NULL, NULL) = 1 (out [1])
write(1, "hi\n", 3) = -1 EAGAIN (Resource temporarily unavailable)
forever.
Then select() should not return fd 1 as writable, at least not
reapeatedly.
Phil.
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This archive was generated by hypermail 2b29 : Thu Jul 31 2003 - 22:00:27 EST