[GitHub] gudegg commented on issue #2578: The current RoundRobinLoadBalance implementation performance is not satisfactory

[GitBox]

gudegg commented on issue #2578: The current RoundRobinLoadBalance 
implementation performance is not satisfactory
URL: 
https://github.com/apache/incubator-dubbo/issues/2578#issuecomment-425625376
 
 
   @kimmking find the greatest common divisor first?
   ```java
   public class RoundRobinLoadBalance extends AbstractLoadBalance {
   
       public static final String NAME = "roundrobin";
   
       private final ConcurrentMap<String, AtomicPositiveInteger> sequences = 
new ConcurrentHashMap<String, AtomicPositiveInteger>();
   
       @Override
       protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, 
Invocation invocation) {
           String key = invokers.get(0).getUrl().getServiceKey() + "." + 
invocation.getMethodName();
           int length = invokers.size(); // Number of invokers
           int maxWeight = 0; // The maximum weight
           int minWeight = Integer.MAX_VALUE; // The minimum weight
           final LinkedHashMap<Invoker<T>, IntegerWrapper> invokerToWeightMap = 
new LinkedHashMap<Invoker<T>, IntegerWrapper>();
           int weightSum = 0;
           int gcd = 0;
           for (int i = 0; i < length; i++) {
               int weight = getWeight(invokers.get(i), invocation);
               if (gcd != 1) {
                   gcd = gcd(weight, gcd);
               }
               maxWeight = Math.max(maxWeight, weight); // Choose the maximum 
weight
               minWeight = Math.min(minWeight, weight); // Choose the minimum 
weight
               if (weight > 0) {
                   invokerToWeightMap.put(invokers.get(i), new 
IntegerWrapper(weight));
                   weightSum += weight;
               }
           }
           AtomicPositiveInteger sequence = sequences.get(key);
           if (sequence == null) {
               sequences.putIfAbsent(key, new AtomicPositiveInteger());
               sequence = sequences.get(key);
           }
           int currentSequence = sequence.getAndIncrement();
           if (maxWeight > 0 && minWeight < maxWeight) {
               int mod = currentSequence % (weightSum / gcd);
               for (int i = 0; i < maxWeight / gcd; i++) {
                   for (Map.Entry<Invoker<T>, IntegerWrapper> each : 
invokerToWeightMap.entrySet()) {
                       final Invoker<T> k = each.getKey();
                       final IntegerWrapper v = each.getValue();
                       if (mod == 0 && v.getValue() > 0) {
                           return k;
                       }
                       if (v.getValue() > 0) {
                           v.decrement(gcd);
                           mod--;
                       }
                   }
               }
           }
           // Round robin
           return invokers.get(currentSequence % length);
       }
   
       private static final class IntegerWrapper {
           private int value;
   
           public IntegerWrapper(int value) {
               this.value = value;
           }
   
           public int getValue() {
               return value;
           }
   
           public void setValue(int value) {
               this.value = value;
           }
   
           public void decrement() {
               this.value--;
           }
   
           public void decrement(int a) {
               this.value -= a;
           }
       }
   
       /**
        * greatest common divisor
        */
       public static int gcd(int number1, int number2) {
           if (number2 == 0) {
               return number1;
           }
           while (true) {
               if ((number1 = number1 % number2) == 0) {
                   return number2;
               }
               if ((number2 = number2 % number1) == 0) {
                   return number1;
               }
           }
       }
   
   }
   ```

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