Added exercise for signal handler

exercises/signal_handler/main.c

@@ -0,0 +1,58 @@
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+volatile sig_atomic_t sigint_caught = 0;
+
+void signal_handler(int signo, siginfo_t *si, void *ucontext)
+{
+	(void)si;
+	(void)ucontext;
+
+	if (signo == SIGINT) {
+		sigint_caught += 1;
+		if (write(STDOUT_FILENO, "Caught SIGINT signal\n", 22) == -1) {
+			_exit(EXIT_FAILURE);
+		}
+		if (sigint_caught >= 3) {
+			if (write(STDOUT_FILENO, "Reach SIGINT limit\n", 20) ==
+			    -1) {
+				_exit(EXIT_FAILURE);
+			}
+			_exit(EXIT_FAILURE);
+		}
+	} else if (signo == SIGUSR1) {
+		if (write(STDOUT_FILENO, "Caught SIGUSR1 signal\n", 23) == -1) {
+			_exit(EXIT_FAILURE);
+		}
+	} else {
+		if (write(STDOUT_FILENO, "Unknown signal\n", 16) == -1) {
+			_exit(EXIT_FAILURE);
+		}
+	}
+}
+
+int main(void)
+{
+	struct sigaction action;
+	sigemptyset(&action.sa_mask);
+	sigaddset(&action.sa_mask, SIGINT);
+	sigaddset(&action.sa_mask, SIGUSR1);
+	action.sa_sigaction = signal_handler;
+	action.sa_flags = SA_SIGINFO;
+
+	if (sigaction(SIGINT, &action, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+	if (sigaction(SIGUSR1, &action, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+
+	printf("Hi, I'm process with PID %d\n", getpid());
+	for (;;)
+		pause();
+	return EXIT_SUCCESS;
+}