Use thread-local randoms.

Author: jpountz

src/main/java/org/elasticsearch/search/aggregations/metrics/percentile/frugal/Frugal.java

@@ -1,5 +1,6 @@
 package org.elasticsearch.search.aggregations.metrics.percentile.frugal;
 
+import jsr166y.ThreadLocalRandom;
 import org.apache.lucene.util.OpenBitSet;
 import org.apache.lucene.util.RamUsageEstimator;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -25,7 +26,7 @@ public class Frugal extends InternalPercentiles.Estimator<Frugal> {
         // if we wanted to do it right... we'd need an "OpenRandom" class where we have access to the current seed
         // and the serialize the seed as well. In our context, it doesn't matter much as the rand is not used once
         // this commulate is transferred (the rand is no used in the reduce phase)
-        this.rand = new Random();
+        this.rand = ThreadLocalRandom.current();
     }
 
     /**
@@ -48,7 +49,7 @@ public Frugal(double[] percents) {
         this.signs = new OpenBitSet(percents.length);
         this.signs.set(0, percents.length);
         Arrays.fill(this.steps, 1);
-        this.rand = new Random();
+        this.rand = ThreadLocalRandom.current();
     }
 
     @Override
@@ -71,12 +72,13 @@ public void offer(double value) {
             return;
         }
 
+        final double randomValue = rand.nextDouble() * 100;
         for (int i = 0 ; i < percents.length; ++i) {
-            offerTo(i, value);
+            offerTo(i, value, randomValue);
         }
     }
 
-    private void offerTo(int index, double value) {
+    private void offerTo(int index, double value, double randomValue) {
 
         double percent = this.percents[index];
 
@@ -92,8 +94,6 @@ private void offerTo(int index, double value) {
             return;
         }
 
-        final double randomValue = this.rand.nextDouble() * 100.0d;
-
         if (value > estimates[index] && randomValue > (100.0d - percent)) {
             steps[index] += signs.get(index) ? 1 : -1;
 

src/main/java/org/elasticsearch/search/aggregations/metrics/percentile/frugal/QuickSelect.java

@@ -1,18 +1,20 @@
 package org.elasticsearch.search.aggregations.metrics.percentile.frugal;
 
 
+import jsr166y.ThreadLocalRandom;
+
 import java.util.Random;
 
 public class QuickSelect {
 
-    private static final Random rand = new Random();
-
     public static double quickSelect(double[] list, int left, int right, int k) {
 
         if (left == right) {
             return list[left];
         }
 
+        final Random rand = ThreadLocalRandom.current();
+
         while (true) {
             int pivot = left + rand.nextInt(right - left + 1);
 

src/main/java/org/elasticsearch/search/aggregations/metrics/percentile/tdigest/TDigestState.java

@@ -22,18 +22,19 @@
  * https://github.com/addthis/stream-lib/blob/master/src/main/java/com/clearspring/analytics/stream/quantile/TDigest.java
  */
 
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Lists;
+import jsr166y.ThreadLocalRandom;
+import org.elasticsearch.common.io.stream.StreamInput;
+import org.elasticsearch.common.io.stream.StreamOutput;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Random;
 import java.util.concurrent.atomic.AtomicInteger;
-import com.google.common.base.Preconditions;
-import com.google.common.collect.Lists;
-import com.sun.jna.Structure;
-import org.elasticsearch.common.io.stream.StreamInput;
-import org.elasticsearch.common.io.stream.StreamOutput;
 
 
 /**
@@ -73,12 +74,8 @@ public class TDigestState {
      *                    accuracy.
      */
     public TDigestState(double compression) {
-        this(compression, new Random());
-    }
-
-    public TDigestState(double compression, Random random) {
         this.compression = compression;
-        gen = random;
+        gen = ThreadLocalRandom.current();
     }
 
     /**
@@ -184,7 +181,7 @@ public static TDigestState merge(double compression, Iterable<TDigestState> subD
         Preconditions.checkArgument(subData.iterator().hasNext(), "Can't merge 0 digests");
         List<TDigestState> elements = Lists.newArrayList(subData);
         int n = Math.max(1, elements.size() / 4);
-        TDigestState r = new TDigestState(compression, elements.get(0).gen);
+        TDigestState r = new TDigestState(compression);
         if (elements.get(0).recordAllData) {
             r.recordAllData();
         }
@@ -203,7 +200,7 @@ public void compress() {
     }
 
     private void compress(GroupTree other) {
-        TDigestState reduced = new TDigestState(compression, gen);
+        TDigestState reduced = new TDigestState(compression);
         if (recordAllData) {
             reduced.recordAllData();
         }