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	Use sigaction(SA_NOCLDWAIT) for SIGCHLD handling - dwm - dynamic window manager
	git clone git://git.suckless.org/dwm
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	---
	commit 712d6639ff8e863560328131bbb92b248dc9cde7
	parent 89f9905714c1c1b2e8b09986dfbeca15b68d8af8
	Author: Chris Down <[email protected]>
	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 …
	theory interrupted).

	POSIX reference:
	"Consequences of Process Termination":
	https://pubs.opengroup.org/onlinepubs/9699919799/functions/_Exit.html#tag_16_01…

	Diffstat:
	M dwm.c \| 20 +++++++++-----------

	1 file changed, 9 insertions(+), 11 deletions(-)
	---
	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)