--- a/jdk/src/share/classes/java/util/HashMap.java Thu May 17 10:06:19 2012 -0700
+++ b/jdk/src/share/classes/java/util/HashMap.java Wed May 30 22:18:37 2012 -0700
@@ -175,6 +175,35 @@
*/
transient int modCount;
+ private static class Holder {
+ /**
+ *
+ */
+ static final sun.misc.Unsafe UNSAFE;
+
+ /**
+ * Offset of "final" hashSeed field we must set in
+ * readObject() method.
+ */
+ static final long HASHSEED_OFFSET;
+
+ static {
+ try {
+ UNSAFE = sun.misc.Unsafe.getUnsafe();
+ HASHSEED_OFFSET = UNSAFE.objectFieldOffset(
+ HashMap.class.getDeclaredField("hashSeed"));
+ } catch (NoSuchFieldException | SecurityException e) {
+ throw new InternalError("Failed to record hashSeed offset", e);
+ }
+ }
+ }
+
+ /**
+ * A randomizing value associated with this instance that is applied to
+ * hash code of keys to make hash collisions harder to find.
+ */
+ transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this);
+
/**
* Constructs an empty <tt>HashMap</tt> with the specified initial
* capacity and load factor.
@@ -200,7 +229,7 @@
capacity <<= 1;
this.loadFactor = loadFactor;
- threshold = (int)(capacity * loadFactor);
+ threshold = (int)Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
table = new Entry[capacity];
init();
}
@@ -221,10 +250,7 @@
* (16) and the default load factor (0.75).
*/
public HashMap() {
- this.loadFactor = DEFAULT_LOAD_FACTOR;
- threshold = (int)(DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
- table = new Entry[DEFAULT_INITIAL_CAPACITY];
- init();
+ this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
}
/**
@@ -255,13 +281,20 @@
}
/**
- * Applies a supplemental hash function to a given hashCode, which
- * defends against poor quality hash functions. This is critical
- * because HashMap uses power-of-two length hash tables, that
+ * Retrieve object hash code and applies a supplemental hash function to the
+ * result hash, which defends against poor quality hash functions. This is
+ * critical because HashMap uses power-of-two length hash tables, that
* otherwise encounter collisions for hashCodes that do not differ
- * in lower bits. Note: Null keys always map to hash 0, thus index 0.
+ * in lower bits.
*/
- static int hash(int h) {
+ final int hash(Object k) {
+ int h = hashSeed;
+ if (k instanceof String) {
+ return ((String)k).hash32();
+ }
+
+ h ^= k.hashCode();
+
// This function ensures that hashCodes that differ only by
// constant multiples at each bit position have a bounded
// number of collisions (approximately 8 at default load factor).
@@ -313,32 +346,9 @@
*/
@SuppressWarnings("unchecked")
public V get(Object key) {
- if (key == null)
- return (V)getForNullKey();
- int hash = hash(key.hashCode());
- for (Entry<?,?> e = table[indexFor(hash, table.length)];
- e != null;
- e = e.next) {
- Object k;
- if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
- return (V)e.value;
- }
- return null;
- }
+ Entry<K,V> entry = getEntry(key);
- /**
- * Offloaded version of get() to look up null keys. Null keys map
- * to index 0. This null case is split out into separate methods
- * for the sake of performance in the two most commonly used
- * operations (get and put), but incorporated with conditionals in
- * others.
- */
- private Object getForNullKey() {
- for (Entry<?,?> e = table[0]; e != null; e = e.next) {
- if (e.key == null)
- return e.value;
- }
- return null;
+ return null == entry ? null : entry.getValue();
}
/**
@@ -360,7 +370,7 @@
*/
@SuppressWarnings("unchecked")
final Entry<K,V> getEntry(Object key) {
- int hash = (key == null) ? 0 : hash(key.hashCode());
+ int hash = (key == null) ? 0 : hash(key);
for (Entry<?,?> e = table[indexFor(hash, table.length)];
e != null;
e = e.next) {
@@ -388,7 +398,7 @@
public V put(K key, V value) {
if (key == null)
return putForNullKey(value);
- int hash = hash(key.hashCode());
+ int hash = hash(key);
int i = indexFor(hash, table.length);
@SuppressWarnings("unchecked")
Entry<K,V> e = (Entry<K,V>)table[i];
@@ -433,7 +443,7 @@
* addEntry.
*/
private void putForCreate(K key, V value) {
- int hash = (key == null) ? 0 : hash(key.hashCode());
+ int hash = null == key ? 0 : hash(key);
int i = indexFor(hash, table.length);
/**
@@ -484,7 +494,7 @@
Entry<?,?>[] newTable = new Entry<?,?>[newCapacity];
transfer(newTable);
table = newTable;
- threshold = (int)(newCapacity * loadFactor);
+ threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
}
/**
@@ -494,19 +504,17 @@
void transfer(Entry<?,?>[] newTable) {
Entry<?,?>[] src = table;
int newCapacity = newTable.length;
- for (int j = 0; j < src.length; j++) {
- Entry<K,V> e = (Entry<K,V>)src[j];
- if (e != null) {
- src[j] = null;
- do {
- Entry<K,V> next = e.next;
- int i = indexFor(e.hash, newCapacity);
- e.next = (Entry<K,V>)newTable[i];
- newTable[i] = e;
- e = next;
- } while (e != null);
+ for (int j = 0; j < src.length; j++ ) {
+ Entry<K,V> e = (Entry<K,V>) src[j];
+ while(null != e) {
+ Entry<K,V> next = e.next;
+ int i = indexFor(e.hash, newCapacity);
+ e.next = (Entry<K,V>) newTable[i];
+ newTable[i] = e;
+ e = next;
}
}
+ Arrays.fill(table, null);
}
/**
@@ -566,7 +574,7 @@
* for this key.
*/
final Entry<K,V> removeEntryForKey(Object key) {
- int hash = (key == null) ? 0 : hash(key.hashCode());
+ int hash = (key == null) ? 0 : hash(key);
int i = indexFor(hash, table.length);
@SuppressWarnings("unchecked")
Entry<K,V> prev = (Entry<K,V>)table[i];
@@ -594,7 +602,8 @@
}
/**
- * Special version of remove for EntrySet.
+ * Special version of remove for EntrySet using {@code Map.Entry.equals()}
+ * for matching.
*/
final Entry<K,V> removeMapping(Object o) {
if (!(o instanceof Map.Entry))
@@ -773,11 +782,13 @@
* Subclass overrides this to alter the behavior of put method.
*/
void addEntry(int hash, K key, V value, int bucketIndex) {
- @SuppressWarnings("unchecked")
- Entry<K,V> e = (Entry<K,V>)table[bucketIndex];
- table[bucketIndex] = new Entry<>(hash, key, value, e);
- if (size++ >= threshold)
+ if ((size >= threshold) && (null != table[bucketIndex])) {
resize(2 * table.length);
+ hash = hash(key);
+ bucketIndex = indexFor(hash, table.length);
+ }
+
+ createEntry(hash, key, value, bucketIndex);
}
/**
@@ -841,7 +852,6 @@
HashMap.this.removeEntryForKey(k);
expectedModCount = modCount;
}
-
}
private final class ValueIterator extends HashIterator<V> {
@@ -1021,9 +1031,8 @@
s.writeInt(size);
// Write out keys and values (alternating)
- if (i != null) {
- while (i.hasNext()) {
- Map.Entry<K,V> e = i.next();
+ if (size > 0) {
+ for(Map.Entry<K,V> e : entrySet0()) {
s.writeObject(e.getKey());
s.writeObject(e.getValue());
}
@@ -1033,26 +1042,50 @@
private static final long serialVersionUID = 362498820763181265L;
/**
- * Reconstitute the <tt>HashMap</tt> instance from a stream (i.e.,
+ * Reconstitute the {@code HashMap} instance from a stream (i.e.,
* deserialize it).
*/
private void readObject(java.io.ObjectInputStream s)
throws IOException, ClassNotFoundException
{
- // Read in the threshold, loadfactor, and any hidden stuff
+ // Read in the threshold (ignored), loadfactor, and any hidden stuff
s.defaultReadObject();
+ if (loadFactor <= 0 || Float.isNaN(loadFactor))
+ throw new InvalidObjectException("Illegal load factor: " +
+ loadFactor);
+
+ // set hashMask
+ Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET,
+ sun.misc.Hashing.randomHashSeed(this));
// Read in number of buckets and allocate the bucket array;
- int numBuckets = s.readInt();
- table = new Entry[numBuckets];
+ s.readInt(); // ignored
+
+ // Read number of mappings
+ int mappings = s.readInt();
+ if (mappings < 0)
+ throw new InvalidObjectException("Illegal mappings count: " +
+ mappings);
+ int initialCapacity = (int) Math.min(
+ // capacity chosen by number of mappings
+ // and desired load (if >= 0.25)
+ mappings * Math.min(1 / loadFactor, 4.0f),
+ // we have limits...
+ HashMap.MAXIMUM_CAPACITY);
+ int capacity = 1;
+ // find smallest power of two which holds all mappings
+ while (capacity < initialCapacity) {
+ capacity <<= 1;
+ }
+
+ table = new Entry[capacity];
+ threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
init(); // Give subclass a chance to do its thing.
- // Read in size (number of Mappings)
- int size = s.readInt();
// Read the keys and values, and put the mappings in the HashMap
- for (int i=0; i<size; i++) {
+ for (int i=0; i<mappings; i++) {
@SuppressWarnings("unchecked")
K key = (K) s.readObject();
@SuppressWarnings("unchecked")