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
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dwm.c
20
dwm.c
@ -205,7 +205,6 @@ static void setmfact(const Arg *arg);
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static void setup(void);
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static void seturgent(Client *c, int urg);
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static void showhide(Client *c);
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static void sigchld(int unused);
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static void spawn(const Arg *arg);
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static void tag(const Arg *arg);
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static void tagmon(const Arg *arg);
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@ -1543,9 +1542,16 @@ setup(void)
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int i;
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XSetWindowAttributes wa;
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Atom utf8string;
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struct sigaction sa;
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/* clean up any zombies immediately */
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sigchld(0);
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/* do not transform children into zombies when they terminate */
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sigemptyset(&sa.sa_mask);
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sa.sa_flags = SA_NOCLDSTOP | SA_NOCLDWAIT | SA_RESTART;
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sa.sa_handler = SIG_IGN;
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sigaction(SIGCHLD, &sa, NULL);
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/* clean up any zombies (inherited from .xinitrc etc) immediately */
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while (waitpid(-1, NULL, WNOHANG) > 0);
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/* init screen */
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screen = DefaultScreen(dpy);
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@ -1638,14 +1644,6 @@ showhide(Client *c)
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}
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}
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void
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sigchld(int unused)
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{
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if (signal(SIGCHLD, sigchld) == SIG_ERR)
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die("can't install SIGCHLD handler:");
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while (0 < waitpid(-1, NULL, WNOHANG));
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}
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void
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spawn(const Arg *arg)
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{
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