flock mechanic added

src/utils.c

@@ -1,15 +1,39 @@
+#include <errno.h>
 #include <fcntl.h>
 #include <glob.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/file.h>
 #include <time.h>
 #include <unistd.h>
 
 #include "log.h"
 #include "utils.h"
 
+int get_instance_lock(void) {
+	const char *xdg_runtime_dir = getenv("XDG_RUNTIME_DIR");
+	char tmp_dir[256];
+	snprintf(tmp_dir, sizeof(tmp_dir), "%s/linuxSmartie.lock", xdg_runtime_dir);
+
+	const int file = open(tmp_dir, O_CREAT | O_RDWR | O_CLOEXEC, 0600);
+	if (file < 0) {
+		applog(LOG_ERR, "Couldn't create a lock file at %s", tmp_dir);
+		return -1;
+	}
+
+	if (flock(file, LOCK_EX | LOCK_NB) < 0) {
+		if (errno == EWOULDBLOCK)
+			applog(LOG_ERR, "another instance already running, this one will exit.");
+		else
+			applog(LOG_ERR, "flock failed: %s", strerror(errno));
+		close(file);
+		return -1;
+	}
+	return 0;
+}
+
 inline void timespec_add_ms(struct timespec *ts, const uint16_t ms) {
 	ts->tv_nsec += ms * 1000000L;
 	if (ts->tv_nsec >= 1000000000L) {