8322149: ConcurrentHashMap smarter presizing for copy constructor and putAll

Reviewed-by: shade, simonis

Author: caojoshua

src/java.base/share/classes/java/util/concurrent/ConcurrentHashMap.java

@@ -848,7 +848,7 @@ public ConcurrentHashMap(int initialCapacity) {
      * @param m the map
      */
     public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
-        this.sizeCtl = DEFAULT_CAPACITY;
+        this(m.size());
         putAll(m);
     }
 
@@ -1084,7 +1084,9 @@ else if (f instanceof ReservationNode)
      * @param m mappings to be stored in this map
      */
     public void putAll(Map<? extends K, ? extends V> m) {
-        tryPresize(m.size());
+        if (table != null) {
+            tryPresize(size() + m.size());
+        }
         for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
             putVal(e.getKey(), e.getValue(), false);
     }

test/micro/org/openjdk/bench/java/util/concurrent/Maps.java

@@ -28,6 +28,7 @@
 import org.openjdk.jmh.annotations.Measurement;
 import org.openjdk.jmh.annotations.Mode;
 import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
 import org.openjdk.jmh.annotations.Scope;
 import org.openjdk.jmh.annotations.Setup;
 import org.openjdk.jmh.annotations.State;
@@ -48,27 +49,32 @@
 public class Maps {
     private SimpleRandom rng;
     private Map<Integer, Integer> map;
+    private Map<Integer, Integer> staticMap;
     private Integer[] key;
 
     private int removesPerMaxRandom;
     private int insertsPerMaxRandom;
     private int total;
     private int position;
 
+    @Param("10000")
+    private int nkeys;
+
     @Setup
     public void initTest() {
-        int nkeys = 10000;
         int pRemove = 10;
         int pInsert = 90;
         removesPerMaxRandom = (int) ((pRemove / 100.0 * 0x7FFFFFFFL));
         insertsPerMaxRandom = (int) ((pInsert / 100.0 * 0x7FFFFFFFL));
 
         rng = new SimpleRandom();
         map = new ConcurrentHashMap<>();
+        staticMap = new ConcurrentHashMap<>();
         total = 0;
         key = new Integer[nkeys];
         for (int i = 0; i < key.length; ++i) {
             key[i] = rng.next();
+            staticMap.put(rng.next(), rng.next());
         }
         position = key.length / 2;
     }
@@ -106,6 +112,21 @@ public void testConcurrentHashMap() {
         position = pos;
     }
 
+    @Benchmark
+    public ConcurrentHashMap<Integer, Integer> testConcurrentHashMapCopyConstructor() {
+        return new ConcurrentHashMap<>(staticMap);
+    }
+
+    @Benchmark
+    public ConcurrentHashMap<Integer, Integer> testConcurrentHashMapPutAll() {
+        ConcurrentHashMap<Integer, Integer> map = new ConcurrentHashMap<>(nkeys);
+        for (int i = 0; i < nkeys; ++i) {
+            map.put(rng.next(), rng.next());
+        }
+        map.putAll(staticMap);
+        return map;
+    }
+
     private static class SimpleRandom {
         private final static long multiplier = 0x5DEECE66DL;
         private final static long addend = 0xBL;