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Re: 2.5.1: kill(pid, sig) before waitpid() returns -1 for sig != 0

Hi Eric,

On Aug 11 11:51, Erik Bray wrote:
> [...]
> > Existing implementations vary on the result of a kill() with pid indicating an inactive process (a
> > terminated process that has not been waited for by its parent). Some indicate success on such a
> > call (subject to permission checking), while others give an error of [ESRCH]. Since the definition
> > of process lifetime in this volume of POSIX.1-2008 covers inactive processes, the [ESRCH] error
> > as described is inappropriate in this case. In particular, this means that an application cannot
> > have a parent process check for termination of a particular child with kill(). (Usually this is done
> > with the null signal; this can be done reliably with waitpid().)
> In response to the originally issue, this was fixed *specifically* for
> the case of kill(pid, 0).  But my reading of the above is that kill()
> should return 0 in this case regardless of the signal (modulo
> permissions, etc.).  On Linux, for example, when calling kill with pid
> of a zombie process the kernel will happily deliver the signal to the
> relevant task_struct; it will just never be acted on since the task
> will never run again.

I'm not sure why cgf only fixed that for sig 0 at the time, since, as
you noted, the text from POSIX-1.2008 does not state that this is
*restricted* to sig 0.

> The below (untested) patch demonstrates the change I'm suggesting,
> though I don't know what other code, if any, might be involved in
> this.

The original patch laid the groundwork by making sure that there are
two states, EXITED and REAPED.  Removing the explicit check for 0 is
the right thing to do, afaics, so I tested and applied your patch as is,


Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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