xds, wrr: randomize the initial deadline in the scheduler (#9922)

xds/src/main/java/io/grpc/xds/WeightedRoundRobinLoadBalancer.java

@@ -64,10 +64,10 @@ final class WeightedRoundRobinLoadBalancer extends RoundRobinLoadBalancer {
   private final Ticker ticker;
 
   public WeightedRoundRobinLoadBalancer(Helper helper, Ticker ticker) {
-    this(new WrrHelper(OrcaOobUtil.newOrcaReportingHelper(helper)), ticker);
+    this(new WrrHelper(OrcaOobUtil.newOrcaReportingHelper(helper)), ticker, new Random());
   }
 
-  public WeightedRoundRobinLoadBalancer(WrrHelper helper, Ticker ticker) {
+  public WeightedRoundRobinLoadBalancer(WrrHelper helper, Ticker ticker, Random random) {
     super(helper);
     helper.setLoadBalancer(this);
     this.ticker = checkNotNull(ticker, "ticker");
@@ -75,7 +75,12 @@ final class WeightedRoundRobinLoadBalancer extends RoundRobinLoadBalancer {
     this.syncContext = checkNotNull(helper.getSynchronizationContext(), "syncContext");
     this.timeService = checkNotNull(helper.getScheduledExecutorService(), "timeService");
     this.updateWeightTask = new UpdateWeightTask();
-    this.random = new Random();
+    this.random = random;
+  }
+
+  @VisibleForTesting
+  WeightedRoundRobinLoadBalancer(Helper helper, Ticker ticker, Random random) {
+    this(new WrrHelper(OrcaOobUtil.newOrcaReportingHelper(helper)), ticker, random);
   }
 
   @Override
@@ -100,8 +105,7 @@ final class WeightedRoundRobinLoadBalancer extends RoundRobinLoadBalancer {
 
   @Override
   public RoundRobinPicker createReadyPicker(List<Subchannel> activeList) {
-    int startIndex = random.nextInt(activeList.size());
+    return new WeightedRoundRobinPicker(activeList);
-    return new WeightedRoundRobinPicker(activeList, startIndex);
   }
 
   private final class UpdateWeightTask implements Runnable {
@@ -228,8 +232,8 @@ final class WeightedRoundRobinLoadBalancer extends RoundRobinLoadBalancer {
     private volatile EdfScheduler scheduler;
     private volatile boolean rrMode;
 
-    WeightedRoundRobinPicker(List<Subchannel> list, int startIndex) {
+    WeightedRoundRobinPicker(List<Subchannel> list) {
-      super(checkNotNull(list, "list"), startIndex);
+      super(checkNotNull(list, "list"), random.nextInt(list.size()));
       Preconditions.checkArgument(!list.isEmpty(), "empty list");
       this.list = list;
       updateWeight();
@@ -266,7 +270,7 @@ final class WeightedRoundRobinLoadBalancer extends RoundRobinLoadBalancer {
         rrMode = true;
         return;
       }
-      EdfScheduler scheduler = new EdfScheduler(list.size());
+      EdfScheduler scheduler = new EdfScheduler(list.size(), random);
       avgWeight /= 1.0 * weightedChannelCount;
       for (int i = 0; i < list.size(); i++) {
         WrrSubchannel subchannel = (WrrSubchannel) list.get(i);
@@ -348,11 +352,13 @@ final class WeightedRoundRobinLoadBalancer extends RoundRobinLoadBalancer {
 
     private final Object lock = new Object();
 
+    private final Random random;
+
     /**
      * Use the item's deadline as the order in the priority queue. If the deadlines are the same,
      * use the index. Index should be unique.
      */
-    EdfScheduler(int initialCapacity) {
+    EdfScheduler(int initialCapacity, Random random) {
       this.prioQueue = new PriorityQueue<ObjectState>(initialCapacity, (o1, o2) -> {
         if (o1.deadline == o2.deadline) {
           return Integer.compare(o1.index, o2.index);
@@ -360,6 +366,7 @@ final class WeightedRoundRobinLoadBalancer extends RoundRobinLoadBalancer {
           return Double.compare(o1.deadline, o2.deadline);
         }
       });
+      this.random = random;
     }
 
     /**
@@ -371,8 +378,8 @@ final class WeightedRoundRobinLoadBalancer extends RoundRobinLoadBalancer {
     void add(int index, double weight) {
       checkArgument(weight > 0.0, "Weights need to be positive.");
       ObjectState state = new ObjectState(Math.max(weight, MINIMUM_WEIGHT), index);
-      state.deadline = 1 / state.weight;
+      // Randomize the initial deadline.
-      // TODO(zivy): randomize the initial deadline.
+      state.deadline = random.nextDouble() * (1 / state.weight);
       prioQueue.add(state);
     }
 

xds/src/test/java/io/grpc/xds/WeightedRoundRobinLoadBalancerTest.java

@@ -171,7 +171,8 @@ public class WeightedRoundRobinLoadBalancerTest {
               return subchannel;
             }
             });
-    wrr = new WeightedRoundRobinLoadBalancer(helper, fakeClock.getDeadlineTicker());
+    wrr = new WeightedRoundRobinLoadBalancer(helper, fakeClock.getDeadlineTicker(),
+        new FakeRandom());
   }
 
   @Test
@@ -625,7 +626,7 @@ public class WeightedRoundRobinLoadBalancerTest {
     double totalWeight = 0;
     int capacity = random.nextInt(10) + 1;
     double[] weights = new double[capacity];
-    EdfScheduler scheduler = new EdfScheduler(capacity);
+    EdfScheduler scheduler = new EdfScheduler(capacity, random);
     for (int i = 0; i < capacity; i++) {
       weights[i] = random.nextDouble();
       scheduler.add(i, weights[i]);
@@ -643,7 +644,7 @@ public class WeightedRoundRobinLoadBalancerTest {
 
   @Test
   public void edsScheduler_sameWeight() {
-    EdfScheduler scheduler = new EdfScheduler(2);
+    EdfScheduler scheduler = new EdfScheduler(2, new FakeRandom());
     scheduler.add(0, 0.5);
     scheduler.add(1, 0.5);
     assertThat(scheduler.pick()).isEqualTo(0);
@@ -670,4 +671,12 @@ public class WeightedRoundRobinLoadBalancerTest {
       return "FakeSocketAddress-" + name;
     }
   }
+
+  private static class FakeRandom extends Random {
+    @Override
+    public double nextDouble() {
+      // return constant value to disable init deadline randomization in the scheduler
+      return 0.322023;
+    }
+  }
 }