Re: [Monotone-devel] auto updates

[Nathaniel Smith]

On Sun, Oct 29, 2006 at 09:13:15AM +0000, Nuno Lucas wrote:
> On 10/29/06, Zack Weinberg <address@hidden> wrote:
> >On 10/29/06, Nathaniel Smith <address@hidden> wrote:
> >>
> >> It should be possible to deal with zombies through some POSIX hackery,
> >> no?  The only tricky bit is that we _do_ sometimes want to wait for a
> >> process, so we can't just unconditionally get rid of zombies...
> >
> >Fork a child, which forks a grandchild and exits.  Grandchild execs
> >what you really wanted to run.  wait() returns for the child, and the
> >grandchild gets reparented to init.
> 
> This seems a bit of a hack when a simple solution is easy.
> 
> Just do this for POSIX systems (I don't believe there is a problem
> with zombie processes on other systems):
> 
> static void signal_handler( int sig, siginfo_t* si, void * context )
> {
>   int status;
>   wait (&status);
> }

FYI, this is a bit buggy -- it can leave zombies if signals get
coalesced, or freeze if other processes might call wait() before the
signal handler runs.

But this technique is what I meant by "unconditionally get rid of
zombies" -- I'm not sure what happens when you have a signal handler
like this, _and_ you sometimes want to call waitpid() in your program
explicitly.

-- Nathaniel

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