Instead of a relative sleep(1), sleep until the full second

This makes sure you don’t lag behind up to nearly one second in
the worst case, depending on the start time of your i3status.

i3status.c

@@ -22,6 +22,8 @@
 #include <glob.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <time.h>
+#include <sys/time.h>
 
 #include "i3status.h"
 
@@ -186,6 +188,8 @@ int main(int argc, char *argv[]) {
         if ((general_socket = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
                 die("Could not create socket\n");
 
+        int interval = cfg_getint(cfg_general, "interval");
+
         while (1) {
                 for (j = 0; j < cfg_size(cfg, "order"); j++) {
                         if (j > 0)
@@ -223,6 +227,13 @@ int main(int argc, char *argv[]) {
                 printf("\n");
                 fflush(stdout);
 
-                sleep(cfg_getint(cfg_general, "interval"));
+                /* To provide updates on every full second (as good as possible)
+                 * we don’t use sleep(interval) but we sleep until the next
+                 * second (with microsecond precision) plus (interval-1)
+                 * seconds. */
+                struct timeval current_time;
+                gettimeofday(&current_time, NULL);
+                struct timespec ts = {interval - 1, (10e5 - current_time.tv_usec) * 1000};
+                nanosleep(&ts, NULL);
         }
 }