add SIGCHLD example

Author: Vladimir Kotal

signals/Makefile

@@ -14,7 +14,8 @@ PROGS=alarm \
 	signal-vs-sigaction \
 	sigsegv \
 	sigwait \
-	sigpending
+	sigpending \
+	sigchld
 
 all: $(PROGS)
 
@@ -72,6 +73,9 @@ sigwait: sigwait.o
 sigpending: sigpending.o
 	$(CC) -o $@ $^
 
+sigchld: sigchld.o
+	$(CC) -o $@ $^
+
 clean:
 	rm -f *.o a.out $(PROGS)
 

signals/sigchld.c

@@ -0,0 +1,42 @@
+/*
+ * The SIGCHLD signal is always delivered to the parent process except
+ * in case it is ignored.
+ */
+
+#include <stdio.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+void
+handler(int s)
+{
+	write(1, "got it\n", 7);
+}
+
+int
+main(int argc, char *argv[])
+{
+	pid_t pid;
+
+#ifdef HANDLE_SIGCHLD
+	struct sigaction act;
+	// act.sa_handler = handler;
+	act.sa_handler = SIG_IGN;
+	sigemptyset(&act.sa_mask);
+	act.sa_flags = 0;
+	sigaction(SIGCHLD, &act, NULL);
+#endif
+
+	if ((pid = fork()) == 0) {
+		sleep(1);
+	} else {
+		int status;
+		printf("forked %d\n", pid);
+		// wait(&status);
+		waitpid(pid, &status, 0);
+	}
+
+	return (0);
+}