Refactor WeightedLoadbalanceStrategy to use a Builder

Signed-off-by: Rossen Stoyanchev <rstoyanchev@vmware.com>

Author: rstoyanchev

rsocket-core/src/main/java/io/rsocket/loadbalance/LoadbalanceRSocketClient.java

@@ -149,7 +149,7 @@ public Builder roundRobinLoadbalanceStrategy() {
      * <p>By default, {@link RoundRobinLoadbalanceStrategy} is used.
      */
     public Builder weightedLoadbalanceStrategy() {
-      this.loadbalanceStrategy = new WeightedLoadbalanceStrategy();
+      this.loadbalanceStrategy = WeightedLoadbalanceStrategy.create();
       return this;
     }
 

rsocket-core/src/main/java/io/rsocket/loadbalance/WeightedLoadbalanceStrategy.java

@@ -20,9 +20,8 @@
 import io.rsocket.core.RSocketConnector;
 import io.rsocket.plugins.RequestInterceptor;
 import java.util.List;
-import java.util.SplittableRandom;
+import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.function.Function;
 import reactor.util.annotation.Nullable;
@@ -37,32 +36,13 @@ public class WeightedLoadbalanceStrategy implements ClientLoadbalanceStrategy {
 
   private static final double EXP_FACTOR = 4.0;
 
-  private static final int EFFORT = 5;
-
-  final int effort;
-  final SplittableRandom splittableRandom;
+  final int maxPairSelectionAttempts;
   final Function<RSocket, WeightedStats> weightedStatsResolver;
 
-  public WeightedLoadbalanceStrategy() {
-    this(new DefaultWeightedStatsResolver());
-  }
-
-  public WeightedLoadbalanceStrategy(Function<RSocket, WeightedStats> weightedStatsResolver) {
-    this(EFFORT, weightedStatsResolver);
-  }
-
-  public WeightedLoadbalanceStrategy(
-      int effort, Function<RSocket, WeightedStats> weightedStatsResolver) {
-    this(effort, new SplittableRandom(System.nanoTime()), weightedStatsResolver);
-  }
-
-  public WeightedLoadbalanceStrategy(
-      int effort,
-      SplittableRandom splittableRandom,
-      Function<RSocket, WeightedStats> weightedStatsResolver) {
-    this.effort = effort;
-    this.splittableRandom = splittableRandom;
-    this.weightedStatsResolver = weightedStatsResolver;
+  private WeightedLoadbalanceStrategy(
+      int numberOfAttempts, @Nullable Function<RSocket, WeightedStats> resolver) {
+    this.maxPairSelectionAttempts = numberOfAttempts;
+    this.weightedStatsResolver = (resolver != null ? resolver : new DefaultWeightedStatsResolver());
   }
 
   @Override
@@ -75,7 +55,7 @@ public void initialize(RSocketConnector connector) {
 
   @Override
   public RSocket select(List<RSocket> sockets) {
-    final int effort = this.effort;
+    final int numberOfAttepmts = this.maxPairSelectionAttempts;
     final int size = sockets.size();
 
     RSocket weightedRSocket;
@@ -103,7 +83,7 @@ public RSocket select(List<RSocket> sockets) {
           RSocket rsc1 = null;
           RSocket rsc2 = null;
 
-          for (int i = 0; i < effort; i++) {
+          for (int i = 0; i < numberOfAttepmts; i++) {
             int i1 = ThreadLocalRandom.current().nextInt(size);
             int i2 = ThreadLocalRandom.current().nextInt(size - 1);
 
@@ -168,30 +148,83 @@ private static double calculateFactor(final double u, final double l, final doub
     return Math.pow(1 + alpha, EXP_FACTOR);
   }
 
-  static class DefaultWeightedStatsResolver implements Function<RSocket, WeightedStats> {
+  /** Create an instance of {@link WeightedLoadbalanceStrategy} with default settings. */
+  public static WeightedLoadbalanceStrategy create() {
+    return new Builder().build();
+  }
+
+  /** Return a builder to create a {@link WeightedLoadbalanceStrategy} with. */
+  public static Builder builder() {
+    return new Builder();
+  }
+
+  /** Builder for {@link WeightedLoadbalanceStrategy}. */
+  public static class Builder {
+
+    private int maxPairSelectionAttempts = 5;
+
+    @Nullable private Function<RSocket, WeightedStats> weightedStatsResolver;
+
+    private Builder() {}
+
+    /**
+     * How many times to try to randomly select a pair of RSocket connections with non-zero
+     * availability. This is applicable when there are more than two connections in the pool. If the
+     * number of attempts is exceeded, the last selected pair is used.
+     *
+     * <p>By default this is set to 5.
+     *
+     * @param numberOfAttempts the iteration count
+     */
+    public Builder maxPairSelectionAttempts(int numberOfAttempts) {
+      this.maxPairSelectionAttempts = numberOfAttempts;
+      return this;
+    }
+
+    /**
+     * Configure how the created {@link WeightedLoadbalanceStrategy} should find the stats for a
+     * given RSocket.
+     *
+     * <p>By default {@code WeightedLoadbalanceStrategy} installs a {@code RequestInterceptor} when
+     * {@link ClientLoadbalanceStrategy#initialize(RSocketConnector)} is called in order to keep
+     * track of stats.
+     *
+     * @param resolver the function to find the stats for an RSocket
+     */
+    public Builder weightedStatsResolver(Function<RSocket, WeightedStats> resolver) {
+      this.weightedStatsResolver = resolver;
+      return this;
+    }
+
+    public WeightedLoadbalanceStrategy build() {
+      return new WeightedLoadbalanceStrategy(
+          this.maxPairSelectionAttempts, this.weightedStatsResolver);
+    }
+  }
+
+  private static class DefaultWeightedStatsResolver implements Function<RSocket, WeightedStats> {
 
-    final ConcurrentMap<RSocket, WeightedStatsRequestInterceptor> rsocketsInterceptors =
-        new ConcurrentHashMap<>();
+    final Map<RSocket, WeightedStats> statsMap = new ConcurrentHashMap<>();
 
     @Override
     public WeightedStats apply(RSocket rSocket) {
-      return rsocketsInterceptors.get(rSocket);
+      return statsMap.get(rSocket);
     }
 
     void init(RSocketConnector connector) {
       connector.interceptors(
-          ir ->
-              ir.forRequester(
+          registry ->
+              registry.forRequester(
                   (Function<RSocket, ? extends RequestInterceptor>)
                       rSocket -> {
                         final WeightedStatsRequestInterceptor interceptor =
                             new WeightedStatsRequestInterceptor() {
                               @Override
                               public void dispose() {
-                                rsocketsInterceptors.remove(rSocket);
+                                statsMap.remove(rSocket);
                               }
                             };
-                        rsocketsInterceptors.put(rSocket, interceptor);
+                        statsMap.put(rSocket, interceptor);
 
                         return interceptor;
                       }));