public class ConcurrentHashMap<K, V> extends AbstractMap<K, V> implements ConcurrentMap<K, V>, Seriablizable {
private static final long serialVersionUID = 7249069246763182397L;
private static final int MAXIMUM_CAPACITY = 1 << 30;
private static final int DEFAULT_CAPACITY = 16;
static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
private static final int DEFAULT_CONCURRENCY_LEVEL = 16;
private static final float LOAD_FACTOR = 0.75f;
static final int TREEIFY_THRESHOLD = 8;
static final int MIN_TREEIFY_CAPACITY = 64;
private static final int MIN_TRANSFER_STRIDE = 16;
private static final int RESIZE_STAMP_BITS = 16;
private static final int MAX_RESIZERS = (1 << (32 - RESIZE_STAMP_BITS)) - 1;
private static final int RESIZE_STAMP_SHIFT = 32 - RESIZE_STAMP_BITS;
static final int MOVED = -1;
static final int TREEBIN = -2;
static final int RESERVED = -3;
static final int HASH_BITS = 0x7fffffff;
static final int NCPU = Runtime.getRuntime().availableProcessors();
}
//内部类
static class Node<K,V> implements Map.Entry<K,V> {
final int hash;
final K key;
volatile V val;
volatile Node<K,V> next;
Node(int hash, K key, V val) { //构造函数，hash值、key值、val值三参
this.hash = hash;
this.key = key;
this.val = val;
}
Node(int hash, K key, V val, Node<K,V> next) { //构造函数，指针，链表
this(hash, key, val);
this.next = next;
}
public final K getKey() { return key; }
public final V getValue() { return val; }
public final int hashCode() { return key.hashCode() ^ val.hashCode(); } ??
public final String toString() { //toString返回格式：类名@16进制无符号整数
return Helpers.mapEntryToString(key, val);
}
public final V setValue(V value) {
throw new UnsupportedOperationException();
}
public final boolean equals(Object o) {
Object k, v, u; Map.Entry<?,?> e;
return ((o instanceof Map.Entry) &&
(k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
(v = e.getValue()) != null &&
(k == key || k.equals(key)) &&
(v == (u = val) || v.equals(u)));
}
/**
* Virtualized support for map.get(); overridden in subclasses.
*/
Node<K,V> find(int h, Object k) {
Node<K,V> e = this;
if (k != null) {
do {
K ek;
if (e.hash == h &&
((ek = e.key) == k || (ek != null && k.equals(ek))))
return e;
} while ((e = e.next) != null);
}
return null;
}
}
public ConcurrentHashMap(){}
public ConcurrentHashMap(int initialCapacity) {
this(initialCapacity, LOAD_FACTOR, 1);
}
public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
this.sizeCtl = DEFAULT_CAPACITY;
putAll(m);
}
//@param concurrencyLevel the estimated number of concurrently updating threads. The implementation may use this value as a sizing hint.
public ConcurrentHashMap(int initialCapacity, float loadFactor, int concurrencyLevel) {
if (!(loadFactor > 0.0f) || initialCapacity < 0 || concurrencyLevel <= 0) throw new IllegalArgumentException();
if (initialCapacity < concurrencyLevel)
initialCapacity = concurrencyLevel;
long size = (long)(1.0 + (long)initialCapacity / loadFactor);
int cap = (size >= (long)MAXIMUM_CAPACITY) ?
MAXIMUM_CAPACITY : tableSizeFor((int)size);
this.sizeCtl = cap;
}
public int size() {
long n = sumCount();
return ((n < 0L) ? 0 :
(n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE :
(int)n);
}
// private static final Unsafe U = Unsafe.getUnsafe();
public V get(Object key) {
Node<K,V>[] tab; Node<K,V> e, p; int n, eh; K ek;
int h = spread(key.hashCode()); //计算哈希值
// static final int spread(int h) {return (h ^ (h >>>16)) & HASH_BITS;}-->增加高位影响，减小哈希冲突（2的幂次方）
// 扰动函数，高16位与低16位进行异或，混合高位低位信息
if ((tab = table) != null && (n = tab.length) > 0 &&
(e = tabAt(tab, (n - 1) & h)) != null) {
// static final <K, V> Node<K, V> tabAt(Node<K, V>[] tab, int i){
//return (Node<K, V>)U.getObjectAcquire(tab, ((long)i << ASHIFT) + ABASE);}
if ((eh = e.hash) == h) { //先根据哈希值查找
if ((ek = e.key) == key || (ek != null && key.equals(ek)))
return e.val;
}
else if (eh < 0)
return (p = e.find(h, key)) != null ? p.val : null; //遍历链表？ find的逻辑与下面的while一致
while ((e = e.next) != null) { //遍历链表
if (e.hash == h &&
((ek = e.key) == key || (ek != null && key.equals(ek))))
return e.val;
}
}
return null;
}
public boolean containsKey(Object key) {
return get(key) != null;
}
public boolean containsValue(Object value) {
if (value == null) throw new NullPointerException();
Node<K, V>[] t;
if ((t = table) != null) {
Traverser<K, V> it = new Traverser<K, V>(t, t.length, 0, t.length);
for (Node<K, V> p; (p = it.advance()) != null;) {
V v;
if ((v = p.val) == value || (v != null && value.equals(v)))
return true;
}
}
return false;
}
public V put(K key, V value) { return putVal(key, value, false)}
final V putVal(K key, V value, boolean onlyIfAbsent) {
if (key == null || value == null) throw new NullPointerException();
int hash = spread(key.hashCode());
int binCount = 0;
for (Node<K,V>[] tab = table;;) {
Node<K,V> f; int n, i, fh; K fk; V fv;
if (tab == null || (n = tab.length) == 0)
tab = initTable();
//static final <K, V> Node<K, V> tabAt(Node<K, V>[] tab, int i) {
//return (Node<K, V>)U.getObjectAcquire(tab, ((long)i << ASHIFT) + ABASE);}
else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
//static final <K, V> boolean casTabAt(Node<K, V>[] tab, int i, Node<K, V> c, Node<K, V> v) {
//return U.compareAndSetObject(tab, ((long)i << ASHIFT) + ABASE, c, v);}
if (casTabAt(tab, i, null, new Node<K,V>(hash, key, value)))
break; // no lock when adding to empty bin
}
else if ((fh = f.hash) == MOVED)
//static final int MOVED = -1; hash for forwarding nodes
tab = helpTransfer(tab, f); //helpTransfer-->如果正在调整大小则帮助转移
else if (onlyIfAbsent // 检查第一个节点但不获取锁
&& fh == hash
&& ((fk = f.key) == key || (fk != null && key.equals(fk)))
&& (fv = f.val) != null)
return fv;
else {
V oldVal = null;
synchronized (f) {
if (tabAt(tab, i) == f) {
if (fh >= 0) {
binCount = 1;
for (Node<K,V> e = f;; ++binCount) {
K ek;
if (e.hash == hash &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
oldVal = e.val;
if (!onlyIfAbsent)
e.val = value;
break;
}
Node<K,V> pred = e;
if ((e = e.next) == null) {
pred.next = new Node<K,V>(hash, key, value);
break;
}
}
}
else if (f instanceof TreeBin) {
Node<K,V> p;
binCount = 2;
if ((p = ((TreeBin<K,V>)f).putTreeVal(hash, key,
value)) != null) {
oldVal = p.val;
if (!onlyIfAbsent)
p.val = value;
}
}
else if (f instanceof ReservationNode)
throw new IllegalStateException("Recursive update");
}
}
if (binCount != 0) {
if (binCount >= TREEIFY_THRESHOLD)
treeifyBin(tab, i);
if (oldVal != null)
return oldVal;
break;
}
}
}
addCount(1L, binCount);
return null;
}
private final Node<K,V>[] initTable() {
Node<K,V>[] tab; int sc;
while ((tab = table) == null || tab.length == 0) {
if ((sc = sizeCtl) < 0)
Thread.yield(); // lost initialization race; just spin
else if (U.compareAndSetInt(this, SIZECTL, sc, -1)) {
try {
if ((tab = table) == null || tab.length == 0) {
int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
@SuppressWarnings("unchecked")
Node<K,V>[] nt = (Node<K,V>[])new Node<?,?>[n];
table = tab = nt;
sc = n - (n >>> 2);
}
} finally {
sizeCtl = sc;
}
break;
}
}
return tab;
}
final Node<K,V>[] helpTransfer(Node<K,V>[] tab, Node<K,V> f) {
Node<K,V>[] nextTab; int sc;
if (tab != null && (f instanceof ForwardingNode) &&
(nextTab = ((ForwardingNode<K,V>)f).nextTable) != null) {
int rs = resizeStamp(tab.length);
while (nextTab == nextTable && table == tab &&
(sc = sizeCtl) < 0) {
if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
sc == rs + MAX_RESIZERS || transferIndex <= 0)
break;
if (U.compareAndSetInt(this, SIZECTL, sc, sc + 1)) {
transfer(tab, nextTab);
break;
}
}
return nextTab;
}
return table;
}