From 0f53ed3c5bc13fe113083c47da30ffc6fc10e855 Mon Sep 17 00:00:00 2001
From: leventov <leventov@ya.ru>
Date: Wed, 17 Sep 2014 21:15:27 +0400
Subject: [PATCH] HCOLL-140 Prevent MultiMaps from occasionally being too dense

---
 .../chronicle/map/VanillaIntIntMultiMap.java  | 19 ++++++++++++++-----
 .../map/VanillaShortShortMultiMap.java        |  8 +++++---
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/src/main/java/net/openhft/chronicle/map/VanillaIntIntMultiMap.java b/src/main/java/net/openhft/chronicle/map/VanillaIntIntMultiMap.java
index 7322bdb9b..aff236ba7 100644
--- a/src/main/java/net/openhft/chronicle/map/VanillaIntIntMultiMap.java
+++ b/src/main/java/net/openhft/chronicle/map/VanillaIntIntMultiMap.java
@@ -27,6 +27,17 @@ import net.openhft.lang.io.DirectStore;
  */
 class VanillaIntIntMultiMap implements IntIntMultiMap {
 
+    static int multiMapCapacity(int minCapacity) {
+        if (minCapacity < 0)
+            throw new IllegalArgumentException();
+        int capacity = Maths.nextPower2(minCapacity, 16);
+        if (((double) minCapacity) / capacity > 2./3.) {
+            // multi map shouldn't be too dense
+            capacity <<= 1;
+        }
+        return capacity;
+    }
+
     private static final int ENTRY_SIZE = 8;
     private static final int ENTRY_SIZE_SHIFT = 3;
     private static final int UNSET_KEY = 0;
@@ -50,9 +61,7 @@ class VanillaIntIntMultiMap implements IntIntMultiMap {
     private long searchPos = -1L;
 
     public VanillaIntIntMultiMap(int minCapacity) {
-        if (minCapacity < 0)
-            throw new IllegalArgumentException();
-        capacity = Maths.nextPower2(minCapacity, 16);
+        capacity = multiMapCapacity(minCapacity);
         capacityMask = capacity - 1;
         capacityMask2 = indexToPos(capacity - 1);
         bytes = DirectStore.allocateLazy(indexToPos(capacity)).bytes();
@@ -75,7 +84,7 @@ class VanillaIntIntMultiMap implements IntIntMultiMap {
      * constructor as the first argument
      */
     public static long sizeInBytes(int minCapacity) {
-        return indexToPos(Maths.nextPower2(minCapacity, 16));
+        return indexToPos(multiMapCapacity(minCapacity));
     }
 
     /**
@@ -84,7 +93,7 @@ class VanillaIntIntMultiMap implements IntIntMultiMap {
      * constructor as the second argument
      */
     public static long sizeOfBitSetInBytes(int minCapacity) {
-        return Maths.nextPower2(minCapacity, 64L) / 8L;
+        return Math.max(multiMapCapacity(minCapacity), 64L) / 8L;
     }
 
     public static ATSDirectBitSet newPositions(int capacity) {
diff --git a/src/main/java/net/openhft/chronicle/map/VanillaShortShortMultiMap.java b/src/main/java/net/openhft/chronicle/map/VanillaShortShortMultiMap.java
index 36de37266..09a8f7171 100644
--- a/src/main/java/net/openhft/chronicle/map/VanillaShortShortMultiMap.java
+++ b/src/main/java/net/openhft/chronicle/map/VanillaShortShortMultiMap.java
@@ -23,6 +23,8 @@ import net.openhft.lang.collection.DirectBitSet;
 import net.openhft.lang.io.Bytes;
 import net.openhft.lang.io.DirectStore;
 
+import static net.openhft.chronicle.map.VanillaIntIntMultiMap.multiMapCapacity;
+
 /**
  * Supports a simple interface for int -> int[] off heap.
  */
@@ -43,9 +45,9 @@ class VanillaShortShortMultiMap implements IntIntMultiMap {
     private int searchPos = -1;
 
     public VanillaShortShortMultiMap(int minCapacity) {
-        if (minCapacity < 0 || minCapacity > (1 << 16))
+        capacity = multiMapCapacity(minCapacity);
+        if (capacity > (1 << 16))
             throw new IllegalArgumentException();
-        capacity = Maths.nextPower2(minCapacity, 16);
         capacityMask = capacity - 1;
         capacityMask2 = (capacity - 1) * ENTRY_SIZE;
         bytes = DirectStore.allocateLazy(capacity * ENTRY_SIZE).bytes();
@@ -68,7 +70,7 @@ class VanillaShortShortMultiMap implements IntIntMultiMap {
      * constructor as the first argument
      */
     public static long sizeInBytes(int minCapacity) {
-        return Maths.nextPower2(minCapacity, 16L) * ENTRY_SIZE;
+        return ((long) multiMapCapacity(minCapacity)) * ENTRY_SIZE;
     }
 
     /**