java多线程ForkJoin分支合并

Posted 2021-07-07 500年

java多线程ForkJoin

1、什么是ForkJoin

ForkJoin在JDK1.7出现，并发执行任务！提高效率。大数据了。
大数据：Map Reduce（把大任务拆分为小任务）

2、 ForkJoin特点：工作窃取

里面维护的是双端队列

3、ForkJoin操作

import java.util.concurrent.RecursiveTask;

public class FrokJoinDemo extends RecursiveTask<Long> {

	private Long s;
	private Long e;

	private Long temp = 2L;

	public FrokJoinDemo(Long s, Long e) {
		this.s = s;
		this.e = e;
	}

	@Override
	protected Long compute() {
		if (e - s < temp) {
			Long sum = 0L;
			for (Long i = s; i <= e; i++) {
				sum += i;
			}
			return sum;
		} else {
			Long middle = (s + e) / 2;// 中间值
			FrokJoinDemo task1 = new FrokJoinDemo(s, middle);
			task1.fork();// 拆分任务，把任务压如线程队列
			FrokJoinDemo task2 = new FrokJoinDemo(middle + 1, e);
			task2.fork();
			return task1.join() + task2.join();
		}
	}
}

测试类

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.stream.LongStream;

public class ForkJoinTest {

	public static void main(String[] args) throws Exception {
		System.out.println("测试计算机配置：");
		System.out.println("CPU:"+Runtime.getRuntime().availableProcessors());
		System.out.println("Java虚拟机运行内存：");
		System.out.println("可用内存总量："+Runtime.getRuntime().totalMemory()/1024/1024+"M");
		System.out.println("=========== 传统方式 =============");
		test1();
		System.out.println("=========== ForkJoin =============");
		test2();
		System.out.println("=========== Stream并行流 =============");
		test3();
	}

	private static void test1() {
		long start = System.currentTimeMillis();
		Long sum = 0L;
		for (Long i = 1L; i <= 10_0000_0000L; i++) {
			sum += i;
		}

		long end = System.currentTimeMillis();
		System.out.println("sum=" + sum + " 时间：" + (end - start));
	}

	private static void test2() throws Exception {
		long start = System.currentTimeMillis();
		ForkJoinPool forkJoinPool = new ForkJoinPool();
		ForkJoinTask<Long> submit = forkJoinPool.submit(new FrokJoinDemo(0L, 10_0000_0000L));
		Long sum = submit.get();

		long end = System.currentTimeMillis();
		System.out.println("sum=" + sum + " 时间：" + (end - start));
	}

	private static void test3() {
		long start = System.currentTimeMillis();

		long sum = LongStream.rangeClosed(0, 10_0000_0000L).parallel().reduce(0, Long::sum);

		long end = System.currentTimeMillis();
		System.out.println("sum=" + sum + " 时间：" + (end - start));
	}

}

运行结果对比

测试计算机配置：
CPU:8
Java虚拟机运行内存：
可用内存总量：121M
=========== 传统方式 =============
sum=500000000500000000 时间：7822
=========== ForkJoin =============
sum=500000000500000000 时间：37865
=========== Stream并行流 =============
sum=500000000500000000 时间：400

特别鸣谢：狂神说Java老师的无私奉献

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