longadder

比AtomicInteger快，但没那么准

主要用到的参数：
base,cells数组，cellsBusy有无锁，uncontended竞争过,各种cas

public void add(long x) {
        //牛逼啊可以修改了 哈哈
        Cell[] as; long b, v; int m; Cell a;
        //说明cells已经初始化了 或者 没有抢到base
        if ((as = cells) != null || !casBase(b = base, b + x)) {
            boolean uncontended = true;
            //cells为空 + 位置没人 + 位置有值但是修改失败
            //需要进入方法去写值
            if (as == null || (m = as.length - 1) < 0 ||
                (a = as[getProbe() & m]) == null ||
                !(uncontended = a.cas(v = a.value, v + x)))
                longAccumulate(x, null, uncontended);
        }
    }

//fn为空的 没起作用
final void longAccumulate(long x, LongBinaryOperator fn,
                              boolean wasUncontended) {
        int h;
        if ((h = getProbe()) == 0) {
            ThreadLocalRandom.current(); // force initialization
            h = getProbe();
            wasUncontended = true;
        }
        boolean collide = false;                // True if last slot nonempty
        for (;;) {
            Cell[] as; Cell a; int n; long v;
            // cells已经初始化
            if ((as = cells) != null && (n = as.length) > 0) {
                // 坑位为空 才可以进去操作
                if ((a = as[(n - 1) & h]) == null) {
                    if (cellsBusy == 0) {       // Try to attach new Cell
                        Cell r = new Cell(x);   // Optimistically create
                        if (cellsBusy == 0 && casCellsBusy()) {
                            boolean created = false;
                            try {               // Recheck under lock
                                Cell[] rs; int m, j;
                                //别人可能进来放入值了
                                if ((rs = cells) != null &&
                                    (m = rs.length) > 0 &&
                                    rs[j = (m - 1) & h] == null) {
                                    rs[j] = r;
                                    created = true;
                                }
                            } finally {
                                cellsBusy = 0;
                            }
                            if (created)
                                break;
                            continue;           // Slot is now non-empty
                        }
                    }
                    collide = false;
                }

                else if (!wasUncontended)       // CAS already known to fail
                    wasUncontended = true;      // Continue after rehash
                else if (a.cas(v = a.value, ((fn == null) ? v + x :
                                             fn.applyAsLong(v, x))))
                    break;
                else if (n >= NCPU || cells != as)
                    collide = false;            // At max size or stale
                else if (!collide)
                    collide = true;
                //反正碰撞 需要扩容
                else if (cellsBusy == 0 && casCellsBusy()) {
                    try {
                        if (cells == as) {      // Expand table unless stale
                            Cell[] rs = new Cell[n << 1];
                            for (int i = 0; i < n; ++i)
                                rs[i] = as[i];
                            cells = rs;
                        }
                    } finally {
                        cellsBusy = 0;
                    }
                    collide = false;
                    continue;                   // Retry with expanded table
                }
                h = advanceProbe(h);
            }
            //都是cells没初始化
            else if (cellsBusy == 0 && cells == as && casCellsBusy()) {
                boolean init = false;
                try {                           // Initialize table
                    //为什么还需要判断 因为别的线程可能进来修改了 并且是改完走了导致上面的的casBusy也为true

                    if (cells == as) {
                        Cell[] rs = new Cell[2];
                        rs[h & 1] = new Cell(x);
                        cells = rs;
                        init = true;
                    }
                } finally {
                    cellsBusy = 0;
                }
                if (init)
                    break;
            }
            else if (casBase(v = base, ((fn == null) ? v + x :
                                        fn.applyAsLong(v, x))))
                break;                          // Fall back on using base
        }
    }

扩容意向false一定不会扩容 true可能扩容