ConcurrentHashMap 分段锁消失之谜-put

阅读java version "1.8.0_91"的ConcurrentHashMap源码发现put，get中分段锁不见了

public V put(K key, V value) {
        return putVal(key, value, false);
    }
//该处说明了ifAbsent也调用该方法
   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;
            if (tab == null || (n = tab.length) == 0)
                tab = initTable();
            else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
            //CAS的方法添加新值 tab这个class偏移量为i的地方，添加一个新的node，无锁无压力
                if (casTabAt(tab, i, null,
                             new Node<K,V>(hash, key, value, null)))
                    break;                   // no lock when adding to empty bin
            }
            else if ((fh = f.hash) == MOVED)
                tab = helpTransfer(tab, f);
            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;
//如果是Absent 仅仅只是影响了该处2句代码
                                    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, null);
                                    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;
                            }
                        }
                    }
                }
                if (binCount != 0) {
                    if (binCount >= TREEIFY_THRESHOLD)
                        treeifyBin(tab, i);
                    if (oldVal != null)
                        return oldVal;
                    break;
                }
            }
        }
        addCount(1L, binCount);
        return null;
    }
//为了搞明白段锁是否消失了所以查看了
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.compareAndSwapInt(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;
    }

/**
 * cas 的用法，如何更新数据 
 */
import java.lang.reflect.Field;
import sun.misc.Unsafe;


public class UnsafeTest {

    private static Unsafe unsafe;

    static {
        try {
            //通过反射获取rt.jar下的Unsafe类
            Field field = Unsafe.class.getDeclaredField("theUnsafe");
            field.setAccessible(true);
            unsafe = (Unsafe) field.get(null);
        } catch (Exception e) {
            System.out.println("Get Unsafe instance occur error"+ e);
        }
    }




    public static void main(String[] args) throws Exception
    {
        Class clazz = Target.class;
        Field[] fields = clazz.getDeclaredFields();
        for (Field f : fields) {
            // 获取属性偏移量，可以通过这个偏移量给属性设置
            System.out.println(f.getName() + ":" + unsafe.objectFieldOffset(f));
        }
        Target target = new Target();
        Field intFiled  =  clazz.getDeclaredField("i")  ;
        int a=(Integer)intFiled.get(target ) ;
        System.out.println("原始值是:"+a);
        
        System.out.println(unsafe.compareAndSwapInt(target, 12, 3, 0));
        int b=(Integer)intFiled.get(target) ;
        System.out.println("改变之后的值是:"+b);
        

    }
}


class Target {
    int i=3;
}