Use sigaction(SA_NOCLDWAIT) for SIGCHLD handling - dwm - dynamic window manager
(HTM) git clone https://git.parazyd.org/dwm
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---
(DIR) commit 712d6639ff8e863560328131bbb92b248dc9cde7
(DIR) parent 89f9905714c1c1b2e8b09986dfbeca15b68d8af8
(HTM) Author: Chris Down <chris@chrisdown.name>
Date: Sat, 28 Jan 2023 12:53:48 +0100
Use sigaction(SA_NOCLDWAIT) for SIGCHLD handling
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 read 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.
Some addditional notes for archival purposes:
* NRK pointed out errno of waitpid could also theoretically get clobbered.
* The original patch was iterated on and modified by NRK and Hiltjo:
* SIG_DFL was changed to SIG_IGN, this is required, atleast on older systems
such as tested on Slackware 11.
* signals are not blocked using sigprocmask, because in theory it would
briefly for example also ignore a SIGTERM signal. It is OK if waitpid() is (in
theory interrupted).
POSIX reference:
"Consequences of Process Termination":
https://pubs.opengroup.org/onlinepubs/9699919799/functions/_Exit.html#tag_16_01_03_01
Diffstat:
M dwm.c | 20 +++++++++-----------
1 file changed, 9 insertions(+), 11 deletions(-)
---
(DIR) diff --git a/dwm.c b/dwm.c
@@ -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);
@@ -1543,9 +1542,16 @@ setup(void)
int i;
XSetWindowAttributes wa;
Atom utf8string;
+ struct sigaction sa;
- /* clean up any zombies immediately */
- sigchld(0);
+ /* do not transform children into zombies when they terminate */
+ sigemptyset(&sa.sa_mask);
+ sa.sa_flags = SA_NOCLDSTOP | SA_NOCLDWAIT | SA_RESTART;
+ sa.sa_handler = SIG_IGN;
+ sigaction(SIGCHLD, &sa, NULL);
+
+ /* clean up any zombies (inherited from .xinitrc etc) immediately */
+ while (waitpid(-1, NULL, WNOHANG) > 0);
/* init screen */
screen = DefaultScreen(dpy);
@@ -1639,14 +1645,6 @@ 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)
{
if (arg->v == dmenucmd)