Merge pull request #323 from pacoyi/AvoidOverflow

Avoid overflow
Netflix · Nov 8, 2017 · f8bb8ea · f8bb8ea
2 parents 2d96971 + 53a2c7d
commit f8bb8ea
Showing 1 changed file with 18 additions and 2 deletions.
diff --git a/ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/AbstractServerPredicate.java b/ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/AbstractServerPredicate.java
@@ -137,6 +137,22 @@ public List<Server> getEligibleServers(List<Server> servers, Object loadBalancer
             return results;            
         }
     }
+
+	/**
+	 * Referenced from RoundRobinRule
+     * Inspired by the implementation of {@link AtomicInteger#incrementAndGet()}.
+     *
+     * @param modulo The modulo to bound the value of the counter.
+     * @return The next value.
+     */
+    private int incrementAndGetModulo(int modulo) {
+        for (;;) {
+            int current = nextIndex.get();
+            int next = (current + 1) % modulo;
+            if (nextIndex.compareAndSet(current, next))
+                return current;
+        }
+    }
 
     /**
      * Choose a random server after the predicate filters a list of servers. Load balancer key 
@@ -160,7 +176,7 @@ public Optional<Server> chooseRoundRobinAfterFiltering(List<Server> servers) {
         if (eligible.size() == 0) {
             return Optional.absent();
         }
-        return Optional.of(eligible.get(nextIndex.getAndIncrement() % eligible.size()));
+        return Optional.of(eligible.get(incrementAndGetModulo(eligible.size())));
     }
 
     /**
@@ -184,7 +200,7 @@ public Optional<Server> chooseRoundRobinAfterFiltering(List<Server> servers, Obj
         if (eligible.size() == 0) {
             return Optional.absent();
         }
-        return Optional.of(eligible.get(nextIndex.getAndIncrement() % eligible.size()));
+        return Optional.of(eligible.get(incrementAndGetModulo(eligible.size())));
     }
 
     /**