Netflix#147: let AIMD grow by configurable amount

concurrency-limits-core/src/main/java/com/netflix/concurrency/limits/limit/AIMDLimit.java

@@ -31,6 +31,7 @@ public static class Builder {
         private int minLimit = 20;
         private int initialLimit = 20;
         private int maxLimit = 200;
+        private int increase = 1;
         private double backoffRatio = 0.9;
         private long timeout = DEFAULT_TIMEOUT;
 
@@ -55,6 +56,12 @@ public Builder backoffRatio(double backoffRatio) {
             return this;
         }
 
+        public Builder increaseBy(int increase) {
+            Preconditions.checkArgument(increase >= 1, "Increase value must be >= 1");
+            this.increase = increase;
+            return this;
+        }
+
         /**
          * Timeout threshold that when exceeded equates to a drop.
          * @param timeout
@@ -75,14 +82,16 @@ public AIMDLimit build() {
     public static Builder newBuilder() {
         return new Builder();
     }
-
+
+    private final int increase;
     private final double backoffRatio;
     private final long timeout;
     private final int minLimit;
     private final int maxLimit;
 
     private AIMDLimit(Builder builder) {
         super(builder.initialLimit);
+        this.increase = builder.increase;
         this.backoffRatio = builder.backoffRatio;
         this.timeout = builder.timeout;
         this.maxLimit = builder.maxLimit;
@@ -96,7 +105,7 @@ protected int _update(long startTime, long rtt, int inflight, boolean didDrop) {
         if (didDrop || rtt > timeout) {
             currentLimit = (int) (currentLimit * backoffRatio);
         } else if (inflight * 2 >= currentLimit) {
-            currentLimit =  currentLimit + 1;
+            currentLimit =  currentLimit + increase;
         }
 
         if (currentLimit >= maxLimit) {