SIGCHLD race condition?

[Nicolas Williams]

I see. Well, it seems that the fundamental problem is that select()
can't be interrupted when the child exits, no? You can't have SIGCHLD
unblock when select() is called...

The pipe solution looks like it would be the most elegant...

The 10 second select() timeout is not too ugly a solution either.
It's only needed when the child fds are closed and you're waiting for
input from the client and for the child to exit.

Nico


On Wed, Sep 26, 2001 at 11:07:27AM -0700, Paul Menage wrote:
> >How about:
> >
> > - selecting for exceptions -- remove dead fildeses from the read/write
> >   select masks (will this catch ptys where the child has close its
> >   stdio?)
> >
> > - if select() will be called only with the client connection socket,
> >   then the child must have closed its stdio -- either check wether the
> >   child is alive or add a timeout to the select() or plain and simply
> >   exit.
> >
> 
> In the situation in question, both channels to the child have been
> closed, and the server knows this. wait_until_can_do_something() does
> check whether the child has exited, but there's a window between the
> check and the call to select() that can cause lockups.
> 
> The server can't exit until it knows that the child has exited, as
> otherwise it can't return the child's exit status to the client. Adding
> a maximum 10 second timeout to select() is the temporary solution that
> we're using, as the problem occurs rarely enough that waiting 10 seconds
> occasionally isn't a problem.
> 
> Paul
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