From d3c15f2866504abc0c9a8e8bbc0d393f0b3bd2ce Mon Sep 17 00:00:00 2001
From: elandau <elandau@netflix.com>
Date: Fri, 22 Mar 2019 06:38:54 -0700
Subject: [PATCH 1/2] AIMD Bounds

---
 .../concurrency/limits/limit/AIMDLimit.java   | 32 +++++++++++++++----
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/concurrency-limits-core/src/main/java/com/netflix/concurrency/limits/limit/AIMDLimit.java b/concurrency-limits-core/src/main/java/com/netflix/concurrency/limits/limit/AIMDLimit.java
index 1addef4c..940d13d6 100644
--- a/concurrency-limits-core/src/main/java/com/netflix/concurrency/limits/limit/AIMDLimit.java
+++ b/concurrency-limits-core/src/main/java/com/netflix/concurrency/limits/limit/AIMDLimit.java
@@ -28,7 +28,9 @@ public final class AIMDLimit extends AbstractLimit {
     private static final long DEFAULT_TIMEOUT = TimeUnit.SECONDS.toNanos(5);
 
     public static class Builder {
-        private int initialLimit = 10;
+        private int minLimit = 20;
+        private int initialLimit = 20;
+        private int maxLimit = 200;
         private double backoffRatio = 0.9;
         private long timeout = DEFAULT_TIMEOUT;
 
@@ -37,6 +39,16 @@ public Builder initialLimit(int initialLimit) {
             return this;
         }
 
+        public Builder minLimit(int minLimit) {
+            this.minLimit = minLimit;
+            return this;
+        }
+
+        public Builder maxLimit(int maxLimit) {
+            this.maxLimit = maxLimit;
+            return this;
+        }
+
         public Builder backoffRatio(double backoffRatio) {
             Preconditions.checkArgument(backoffRatio < 1.0 && backoffRatio >= 0.5, "Backoff ratio must be in the range [0.5, 1.0)");
             this.backoffRatio = backoffRatio;
@@ -66,24 +78,32 @@ public static Builder newBuilder() {
     
     private final double backoffRatio;
     private final long timeout;
+    private final int minLimit;
+    private final int maxLimit;
 
     private AIMDLimit(Builder builder) {
         super(builder.initialLimit);
         this.backoffRatio = builder.backoffRatio;
         this.timeout = builder.timeout;
+        this.maxLimit = builder.maxLimit;
+        this.minLimit = builder.minLimit;
     }
     
     @Override
     protected int _update(long startTime, long rtt, int inflight, boolean didDrop) {
-        final int currentLimit = getLimit();
+        int currentLimit = getLimit();
 
         if (didDrop || rtt > timeout) {
-            return Math.max(1, Math.min(currentLimit - 1, (int) (currentLimit * backoffRatio)));
+            currentLimit = (int) (currentLimit * backoffRatio);
         } else if (inflight * 2 >= currentLimit) {
-            return currentLimit + 1;
-        } else {
-            return currentLimit;
+            currentLimit =  currentLimit + 1;
+        }
+
+        if (currentLimit >= maxLimit) {
+            currentLimit = currentLimit / 2;
         }
+
+        return Math.min(maxLimit, Math.max(minLimit, currentLimit));
     }
 
     @Override

From afbbed455123f9d8318e9a7001e085da27d68ab1 Mon Sep 17 00:00:00 2001
From: elandau <elandau@netflix.com>
Date: Fri, 22 Mar 2019 17:31:33 -0700
Subject: [PATCH 2/2] Fix unit test

---
 .../netflix/concurrency/limits/limit/AIMDLimitTest.java   | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/concurrency-limits-core/src/test/java/com/netflix/concurrency/limits/limit/AIMDLimitTest.java b/concurrency-limits-core/src/test/java/com/netflix/concurrency/limits/limit/AIMDLimitTest.java
index 4e08e39a..d4379c57 100644
--- a/concurrency-limits-core/src/test/java/com/netflix/concurrency/limits/limit/AIMDLimitTest.java
+++ b/concurrency-limits-core/src/test/java/com/netflix/concurrency/limits/limit/AIMDLimitTest.java
@@ -14,15 +14,15 @@ public void testDefault() {
     
     @Test
     public void increaseOnSuccess() {
-        AIMDLimit limiter = AIMDLimit.newBuilder().initialLimit(10).build();
+        AIMDLimit limiter = AIMDLimit.newBuilder().initialLimit(20).build();
         limiter.onSample(0, TimeUnit.MILLISECONDS.toNanos(1), 10, false);
-        Assert.assertEquals(11, limiter.getLimit());
+        Assert.assertEquals(21, limiter.getLimit());
     }
 
     @Test
     public void decreaseOnDrops() {
-        AIMDLimit limiter = AIMDLimit.newBuilder().initialLimit(10).build();
+        AIMDLimit limiter = AIMDLimit.newBuilder().initialLimit(30).build();
         limiter.onSample(0, 0, 0, true);
-        Assert.assertEquals(9, limiter.getLimit());
+        Assert.assertEquals(27, limiter.getLimit());
     }
 }