From 712d6639ff8e863560328131bbb92b248dc9cde7 Mon Sep 17 00:00:00 2001 From: Chris Down Date: Sat, 28 Jan 2023 12:53:48 +0100 Subject: 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 --- dwm.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-) diff --git a/dwm.c b/dwm.c index 03baf42b..c2bd8710 100644 --- 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); @@ -1638,14 +1644,6 @@ 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) { -- cgit v1.2.3