Fork/Join 框架与传统线程池的区别采用“工作窃取”模式（work-stealing）：当执行新的任务时它可以将其拆分分成更小的任务执行，并将小任务加到线程队列中，然后再从一个随机线程的队列中偷一个并把它放在自己的队列中。
相对于一般的线程池实现,fork/join框架的优势体现在对其中包含的任务的处理方式上.在一般的线程池中,如果一个线程正在执行的任务由于某些原因无法继续运行,那么该线程会处于等待状态.而在fork/join框架实现中,如果某个子问题由于等待另外一个子问题的完成而无法继续运行.那么处理该子问题的线程会主动寻找其他尚未运行的子问题来执行.这种方式减少了线程的等待时间,提高了性能.
代码体验效果：
import java.util.concurrent.RecursiveTask; public class ForkJoinCalculate extends RecursiveTask<Long>{ /** * */ private static final long serialVersionUID = 13475679780L; private long start; private long end; private static final long THRESHOLD = 10000L; //临界值 public ForkJoinCalculate(long start, long end) { this.start = start; this.end = end; } @Override protected Long compute() { long length = end - start; if(length <= THRESHOLD){ long sum = 0; for (long i = start; i <= end; i++) { sum += i; } return sum; }else{ long middle = (start + end) / 2; ForkJoinCalculate left = new ForkJoinCalculate(start, middle); left.fork(); //拆分，并将该子任务压入线程队列 ForkJoinCalculate right = new ForkJoinCalculate(middle+1, end); right.fork(); return left.join() + right.join(); } } }
测试类：
import java.util.concurrent.ForkJoinPool; import java.util.concurrent.ForkJoinTask; import java.util.stream.LongStream; import org.junit.Test; public class TestForkJoin { static long num = 10000000000000L; @Test public void test1(){ long start = System.currentTimeMillis(); ForkJoinPool pool = new ForkJoinPool(); ForkJoinTask<Long> task = new ForkJoinCalculate(0L, num); long sum = pool.invoke(task); System.out.println(sum); long end = System.currentTimeMillis(); System.out.println("test1耗费的时间为: " + (end - start)); //112-1953-1988-2654-2647-20663-113808 } @Test public void test2(){ long start = System.currentTimeMillis(); long sum = 0L; for (long i = 0L; i <= num; i++) { sum += i; } System.out.println(sum); long end = System.currentTimeMillis(); System.out.println("test2耗费的时间为: " + (end - start)); //34-3174-3132-4227-4223-31583 } @Test public void test3(){ long start = System.currentTimeMillis(); Long sum = LongStream.rangeClosed(0L, num) .parallel() .sum(); System.out.println(sum); long end = System.currentTimeMillis(); System.out.println("test3耗费的时间为: " + (end - start)); //2061-2053-2086-18926 } }
