SIGCHLD race condition?

Nicolas Williams Nicolas.Williams at
Thu Oct 4 04:53:15 EST 2001

On Wed, Oct 03, 2001 at 01:47:59PM -0500, mouring at wrote:
> On Wed, 3 Oct 2001, Nicolas Williams wrote:
> > It's a neat trick. SIGCHLD arrives and the handler reaps the child and
> > writes a byte to this place holder pipe, then, when the select() loop is
> > entered you come out because there's that byte in the pipe, you check
> > the child terminated variable and you exit. No more race condition.
> >
> Neat trick, but I've seen scp terminate with a SIGCHLD before the pipe was
> empty.

There's no such pipe in the code now. It'd be merely a place holder to
tie the SIGCHLD/wait() event to select().

SSHD would still only exit IFF (child is dead && child fildes are dead).

The pipe trick is merely a race avoidance technique.

> I guess I'd have to see the code since I get a feeling we could lose data
> on non-interactive session with this trick.  I'd rather track down what C
> code is holding the offending file descriptor past's the due date and
> rework the code.  I'm not too much a fan of repeating the last 'scp
> missing data' thread.

Wrong thread, methinks. This is the sigchld-arrived-before-entering-
waiting-forever-in-select()-for-the-client-to-send-something thread.

> But I'd be damned if I can find it.  <frown>
> - Ben

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