Expose internal timer_purge() as isc_timer_purge()

This function is used in a unit test to check for data races.

lib/isc/include/isc/timer.h

@@ -224,6 +224,21 @@ isc_timer_touch(isc_timer_t *timer);
  *\li	Unexpected error
  */
 
+void
+isc_timer_purge(isc_timer_t *timer);
+/*%<
+ * Purge timer.
+ *
+ * Requires:
+ *
+ *\li	'timer' points to a valid timer.
+ *
+ * Ensures:
+ *
+ *\li	Any events already posted by the timer are purged.
+ *
+ */
+
 void
 isc_timer_destroy(isc_timer_t **timerp);
 /*%<

lib/isc/timer.c

@@ -469,6 +469,15 @@ isc_timer_touch(isc_timer_t *timer) {
 	return (result);
 }
 
+void
+isc_timer_purge(isc_timer_t *timer) {
+	REQUIRE(VALID_TIMER(timer));
+
+	LOCK(&timer->lock);
+	timer_purge(timer);
+	UNLOCK(&timer->lock);
+}
+
 void
 isc_timer_destroy(isc_timer_t **timerp) {
 	isc_timer_t *timer = NULL;