Force wait queue handler to wake up every time a request is queue

JAVA-3400

Author: jyemin

driver-core/src/main/com/mongodb/internal/connection/BaseCluster.java

@@ -255,7 +255,7 @@ protected synchronized void updateDescription(final ClusterDescription newDescri
         }
 
         description = newDescription;
-        phase.getAndSet(new CountDownLatch(1)).countDown();
+        updatePhase();
     }
 
     protected void fireChangeEvent(final ClusterDescriptionChangedEvent event) {
@@ -267,6 +267,10 @@ public ClusterDescription getCurrentDescription() {
         return description;
     }
 
+    private synchronized void updatePhase() {
+        phase.getAndSet(new CountDownLatch(1)).countDown();
+    }
+
     private long getMaxWaitTimeNanos() {
         if (settings.getServerSelectionTimeout(NANOSECONDS) < 0) {
             return Long.MAX_VALUE;
@@ -463,6 +467,8 @@ private synchronized void notifyWaitQueueHandler(final ServerSelectionRequest re
                 waitQueueHandler = new Thread(new WaitQueueHandler(), "cluster-" + clusterId.getValue());
                 waitQueueHandler.setDaemon(true);
                 waitQueueHandler.start();
+            } else {
+                updatePhase();
             }
         }
     }