update that how to judge the same weight (apache#6479)

update that weights and how to judge the index depend on offset

Co-authored-by: yangmengle <yangmengle>

dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/loadbalance/RandomLoadBalance.java

@@ -49,20 +49,17 @@ protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation
         int length = invokers.size();
         // Every invoker has the same weight?
         boolean sameWeight = true;
-        // the weight of every invokers
+        // the maxWeight of every invokers, the minWeight = 0 or the maxWeight of the last invoker
         int[] weights = new int[length];
-        // the first invoker's weight
-        int firstWeight = getWeight(invokers.get(0), invocation);
-        weights[0] = firstWeight;
         // The sum of weights
-        int totalWeight = firstWeight;
-        for (int i = 1; i < length; i++) {
+        int totalWeight = 0;
+        for (int i = 0; i < length; i++) {
             int weight = getWeight(invokers.get(i), invocation);
-            // save for later use
-            weights[i] = weight;
             // Sum
             totalWeight += weight;
-            if (sameWeight && weight != firstWeight) {
+            // save for later use
+            weights[i] = totalWeight;
+            if (sameWeight && totalWeight != weight * (i + 1)) {
                 sameWeight = false;
             }
         }
@@ -71,8 +68,7 @@ protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation
             int offset = ThreadLocalRandom.current().nextInt(totalWeight);
             // Return a invoker based on the random value.
             for (int i = 0; i < length; i++) {
-                offset -= weights[i];
-                if (offset < 0) {
+                if (offset < weights[i]) {
                     return invokers.get(i);
                 }
             }