[hackers] Re: [dwm][PATCH v2] Use sigaction(SA_NOCLDWAIT) for SIGCHLD handling

From: NRK <nrk_AT_disroot.org>
Date: Sat, 6 Aug 2022 04:16:12 +0600

On Wed, Jul 27, 2022 at 07:36:28AM +0100, Chris Down wrote:
> signal() semantics are pretty unclearly specified. For example,
> depending on OS kernel and libc, the handler may be returned to SIG_DFL
> (hence the inner call to readd the signal handler). Moving to
> sigaction() means the behaviour is consistently defined.
>
> Using SA_NOCLDWAIT also allows us to avoid calling the non-reentrant
> function die() in the handler.
>
> waitpid() and sigaction() can also fail with EINTR, which may mean our
> zombie handling fails, so block signals while setting things up to be
> careful.
> ---
> dwm.c | 25 ++++++++++++++-----------
> 1 file changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/dwm.c b/dwm.c
> index b3c43ee..963baca 100644
> --- a/dwm.c
> +++ b/dwm.c
> _AT_@ -205,7 +205,6 @@ static void setmfact(const Arg *arg);
> static void setup(void);
> static void seturgent(Client *c, int urg);
> static void showhide(Client *c);
> -static void sigchld(int unused);
> static void spawn(const Arg *arg);
> static void tag(const Arg *arg);
> static void tagmon(const Arg *arg);
> _AT_@ -1537,11 +1536,23 @@ void
> setup(void)
> {
> int i;
> + sigset_t sm, oldsm;
> XSetWindowAttributes wa;
> Atom utf8string;
> + const struct sigaction sc = {
> + .sa_handler = SIG_DFL,
> + .sa_flags = SA_RESTART | SA_NOCLDWAIT | SA_NOCLDSTOP,
> + };
> +
> + sigfillset(&sm);
> + sigprocmask(SIG_SETMASK, &sm, &oldsm);
>
> - /* clean up any zombies immediately */
> - sigchld(0);
> + if (sigaction(SIGCHLD, &sc, NULL) < 0)
> + die("sigaction failed:");
> + /* for zombies inherited before SA_NOCLDWAIT from .xinitrc, etc */
> + while (waitpid(-1, NULL, WNOHANG) > 0);
> +
> + sigprocmask(SIG_SETMASK, &oldsm, NULL);
>
> /* init screen */
> screen = DefaultScreen(dpy);
> _AT_@ -1635,14 +1646,6 @@ showhide(Client *c)
> }
> }
>
> -void
> -sigchld(int unused)
> -{
> - if (signal(SIGCHLD, sigchld) == SIG_ERR)
> - die("can't install SIGCHLD handler:");
> - while (0 < waitpid(-1, NULL, WNOHANG));
> -}
> -
> void
> spawn(const Arg *arg)
> {
> --
> 2.37.1
>

ping!

In case this got lost in the noise :)

- NRK
Received on Sat Aug 06 2022 - 00:16:12 CEST