LongAccumulator

LongAdder类是LongAccumulator的一个特例，它提供给用户一个自定义规则的可能——accumulatorFunction.

public LongAccumulator(LongBinaryOperator accumulatorFunction,
                       long identity) {
    this.function = accumulatorFunction;
    base = this.identity = identity;
}

• java.util.function.LongBinaryOperator

@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
     */
    long applyAsLong(long left, long right);
}

LongBinaryOperator是一个lambda表达式接口，(a,b)->c,输入left和right返回一个long值.

LongAccumulator可以实现初始化自定义，LongAdder默认是0，同时，通过LongBinaryOperator，我们可以实现一些计算过程.

LongAccumulator示例

package com.tea.modules.java8.thread.atomic;

import java.util.concurrent.atomic.LongAccumulator;
import java.util.concurrent.atomic.LongAdder;
import java.util.function.LongBinaryOperator;

/**
 * com.tea.modules.java8.thread.atomic
 * LongAccumulator学习
 *
 * @author jaymin
 * @since 2022/11/7
 */
public class LongAccumulatorDemo {
    public static void main(String[] args) {
        // left代表base的值，也就是1；
        // right代表的是传进来的值，也就下面accumulate函数传的值
        LongAccumulator longAccumulator = new LongAccumulator((left, right) -> left * right, 1);
        longAccumulator.accumulate(2);
        System.out.println(longAccumulator.get());

        LongAdder longAdder = new LongAdder();
        longAdder.add(1);
        System.out.println(longAdder.longValue());

        LongAccumulator longAdd = new LongAccumulator(Long::sum, 0);
        longAdd.accumulate(1);
        System.out.println(longAdd.get());
    }
}

这里展示了2个示例，一个是声明一个累乘计算器，一个是用LongAccumulator实现了一个LongAdder.

源码对比

• java.util.concurrent.atomic.LongAccumulator#accumulate

public void accumulate(long x) {
    Cell[] as; long b, v, r; int m; Cell a;
    if ((as = cells) != null ||
        // casBase采用的是lambda表达式返回的值
        (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);
    }
}

• java.util.concurrent.atomic.LongAdder#add

public void add(long x) {
    Cell[] as; long b, v; int m; Cell a;
    // casBase采用的是 b+x
    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);
    }
}