+
+/* Arrange for SIGALRM to be delivered in TIMEOUT seconds. This uses
+ setitimer where available, alarm otherwise.
+
+ TIMEOUT should be non-zero. If the timeout value is so small that
+ it would be rounded to zero, it is rounded to the least legal value
+ instead (1us for setitimer, 1s for alarm). That ensures that
+ SIGALRM will be delivered in all cases. */
+
+static void
+alarm_set (double timeout)
+{
+#ifdef ITIMER_REAL
+ /* Use the modern itimer interface. */
+ struct itimerval itv;
+ memset (&itv, 0, sizeof (itv));
+ itv.it_value.tv_sec = (long) timeout;
+ itv.it_value.tv_usec = 1000000L * (timeout - (long)timeout);
+ if (itv.it_value.tv_sec == 0 && itv.it_value.tv_usec == 0)
+ /* Ensure that we wait for at least the minimum interval.
+ Specifying zero would mean "wait forever". */
+ itv.it_value.tv_usec = 1;
+ setitimer (ITIMER_REAL, &itv, NULL);
+#else /* not ITIMER_REAL */
+ /* Use the old alarm() interface. */
+ int secs = (int) timeout;
+ if (secs == 0)
+ /* Round TIMEOUTs smaller than 1 to 1, not to zero. This is
+ because alarm(0) means "never deliver the alarm", i.e. "wait
+ forever", which is not what someone who specifies a 0.5s
+ timeout would expect. */
+ secs = 1;
+ alarm (secs);
+#endif /* not ITIMER_REAL */
+}
+
+/* Cancel the alarm set with alarm_set. */
+
+static void
+alarm_cancel (void)
+{
+#ifdef ITIMER_REAL
+ struct itimerval disable;
+ memset (&disable, 0, sizeof (disable));
+ setitimer (ITIMER_REAL, &disable, NULL);
+#else /* not ITIMER_REAL */
+ alarm (0);
+#endif /* not ITIMER_REAL */
+}
+