diff options
| author | Chris Down <chris@chrisdown.name> | 2023-01-28 12:53:48 +0100 |
|---|---|---|
| committer | Hiltjo Posthuma <hiltjo@codemadness.org> | 2023-01-28 13:34:43 +0100 |
| commit | 712d6639ff8e863560328131bbb92b248dc9cde7 (patch) | |
| tree | c563872871c1e3e947d40caae45614498140e8dd | |
| parent | 89f9905714c1c1b2e8b09986dfbeca15b68d8af8 (diff) | |
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
| -rw-r--r-- | dwm.c | 20 |
1 files changed, 9 insertions, 11 deletions
@@ -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) |