比LongAddr功能更强大的LongAccumulator原子类原理探究

面试题

（1）LongAccumulator与LongAddr类的结构

（2）LongAddr与LongAccumulator类有什么区别？

LongAccumulator类原理分析

/**
 * Creates a new instance using the given accumulator function
 * and identity element.
 * @param accumulatorFunction a side-effect-free function of two arguments
 * @param identity identity (initial value) for the accumulator function
 */
public LongAccumulator(LongBinaryOperator accumulatorFunction,
                       long identity) {
    this.function = accumulatorFunction;
    base = this.identity = identity;
}

@FunctionalInterface
public interface LongBinaryOperator {

    /**
     * Applies this operator to the given operands.
     *
     * @param left the first operand
     * @param right the second operand
     * @return the operator result
     */
    //根据两个参数计算并返回一个值
    long applyAsLong(long left, long right);
}

如何使用LongAccumulator

LongAdder longAdder = new LongAdder();
new LongAccumulator(new LongBinaryOperator() {
    @Override
    public long applyAsLong(long left, long right) {
        return left+right;
    }
},0);

LongAddr的add方法

public void add(long x) {
    Cell[] as; long b, v; int m; Cell a;
    if ((as = cells) != null || !casBase(b = base, b + x)) {
        boolean uncontended = true;
        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);
    }
}

LongAccumulator的accumulate方法

public void accumulate(long x) {
    Cell[] as; long b, v, r; int m; Cell a;
    if ((as = cells) != null ||
        (r = function.applyAsLong(b = base, x)) != b && !casBase(b, r)) {
        boolean uncontended = true;
        if (as == null || (m = as.length - 1) < 0 ||
            (a = as[getProbe() & m]) == null ||
            !(uncontended =
              (r = function.applyAsLong(v = a.value, x)) == v ||
              a.cas(v, r)))
            longAccumulate(x, function, uncontended);
    }
}

（3）LongAddr与LongAccumulator类相同点？

参考书籍：

Java并发编程之美