Eliminate Strategy abstraction

Simplify builders
New Gradient2 algo

concurrency-limits-core/src/main/java/com/netflix/concurrency/limits/Limit.java

@@ -1,49 +1,29 @@
 package com.netflix.concurrency.limits;
 
+import java.util.function.Consumer;
+
 /**
  * Contract for an algorithm that calculates a concurrency limit based on 
  * rtt measurements
  */
 public interface Limit {
-    /**
-     * Details of the current sample window
-     */
-    interface SampleWindow {
-        /**
-         * @return Candidate RTT in the sample window. This is traditionally the minimum rtt.
-         */
-        long getCandidateRttNanos();
-
-        /**
-         * @return Average RTT in the sample window.  Excludes timeouts and dropped rtt.
-         */
-        long getAverateRttNanos();
-
-        /**
-         * @return Maximum number of inflight observed during the sample window
-         */
-        int getMaxInFlight();
-
-        /**
-         * @return Number of observed RTTs in the sample window
-         */
-        int getSampleCount();
-
-        /**
-         * @return True if there was a timeout
-         */
-        boolean didDrop();
-    }
-
     /**
      * @return Current estimated limit
      */
     int getLimit();
-
+
+    /**
+     * Register a callback to receive notification whenever the limit is updated to a new value
+     * @param consumer
+     */
+    void notifyOnChange(Consumer<Integer> consumer);
+
     /**
-     * Update the concurrency limit using a new rtt sample
-     * 
-     * @param sample Data from the last sampling window such as RTT
+     * Update the limiter with a sample
+     * @param startTime
+     * @param rtt
+     * @param inflight
+     * @param didDrop
      */
-    void update(SampleWindow sample);
+    void onSample(long startTime, long rtt, int inflight, boolean didDrop);
 }

concurrency-limits-core/src/main/java/com/netflix/concurrency/limits/Limiter.java

@@ -1,7 +1,5 @@
 package com.netflix.concurrency.limits;
 
-import com.netflix.concurrency.limits.strategy.LookupPartitionStrategy;
-
 import java.util.Optional;
 
 /**
@@ -40,8 +38,7 @@ interface Listener {
      * If acquired the caller must call one of the Listener methods when the operation has been completed
      * to release the count.
      * 
-     * @param context Context for the request. The context is used by advanced startegies such as 
-     *                  {@link LookupPartitionStrategy}.
+     * @param context Context for the request
      * @return Optional.empty() if limit exceeded.
      */
     Optional<Listener> acquire(ContextT context);

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

@@ -6,7 +6,7 @@
  * Loss based dynamic {@link Limit} that does an additive increment as long as 
  * there are no errors and a multiplicative decrement when there is an error.
  */
-public final class AIMDLimit implements Limit {
+public final class AIMDLimit extends AbstractLimit {
 
     public static class Builder {
         private int initialLimit = 10;
@@ -31,30 +31,26 @@ public static Builder newBuilder() {
         return new Builder();
     }
 
-    private volatile int limit;
     private final double backoffRatio;
 
     private AIMDLimit(Builder builder) {
-        this.limit = builder.initialLimit;
+        super(builder.initialLimit);
         this.backoffRatio = builder.backoffRatio;
     }
 
     @Override
-    public int getLimit() {
-        return limit;
-    }
-
-    @Override
-    public void update(SampleWindow sample) {
-        if (sample.didDrop()) {
-            limit = Math.max(1, Math.min(limit - 1, (int) (limit * backoffRatio)));
-        } else if (sample.getMaxInFlight() >= limit) {
-            limit = limit + 1;
+    protected int _update(long startTime, long rtt, int inflight, boolean didDrop) {
+        if (didDrop) {
+            return Math.max(1, Math.min(getLimit() - 1, (int) (getLimit() * backoffRatio)));
+        } else if (inflight >= getLimit()) {
+            return getLimit() + 1;
+        } else {
+            return getLimit();
         }
     }
 
     @Override
     public String toString() {
-        return "AIMDLimit [limit=" + limit + "]";
+        return "AIMDLimit [limit=" + getLimit() + "]";
     }
 }

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

@@ -0,0 +1,41 @@
+package com.netflix.concurrency.limits.limit;
+
+import com.netflix.concurrency.limits.Limit;
+
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.function.Consumer;
+
+public abstract class AbstractLimit implements Limit {
+    private volatile int limit;
+    private final List<Consumer<Integer>> listeners = new CopyOnWriteArrayList<>();
+
+    protected AbstractLimit(int initialLimit) {
+        this.limit = initialLimit;
+    }
+
+    @Override
+    public final synchronized void onSample(long startTime, long rtt, int inflight, boolean didDrop) {
+        setLimit(_update(startTime, rtt, inflight, didDrop));
+    }
+
+    protected abstract int _update(long startTime, long rtt, int inflight, boolean didDrop);
+
+    @Override
+    public final int getLimit() {
+        return limit;
+    }
+
+    protected synchronized void setLimit(int newLimit) {
+        if (newLimit != limit) {
+            limit = newLimit;
+            listeners.forEach(listener -> listener.accept(newLimit));
+        }
+    }
+
+    public void notifyOnChange(Consumer<Integer> consumer) {
+        this.listeners.add(consumer);
+    }
+
+
+}

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

@@ -1,33 +1,25 @@
 package com.netflix.concurrency.limits.limit;
 
-import com.netflix.concurrency.limits.Limit;
-
 /**
  * Non dynamic limit with fixed value
  */
-public final class FixedLimit implements Limit {
-
-    private final int limit;
+public final class FixedLimit extends AbstractLimit {
 
     public static FixedLimit of(int limit) {
         return new FixedLimit(limit);
     }
 
     private FixedLimit(int limit) {
-        this.limit = limit;
-    }
-
-    @Override
-    public int getLimit() {
-        return limit;
+        super(limit);
     }
 
     @Override
-    public void update(SampleWindow sample) {
+    public int _update(long startTime, long rtt, int inflight, boolean didDrop) {
+        return getLimit();
     }
 
     @Override
     public String toString() {
-        return "FixedLimit [limit=" + limit + "]";
+        return "FixedLimit [limit=" + getLimit() + "]";
     }
 }