代码
import java.util.Random;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;
public class RandomNumSumDemo {
public static void main(String[] args) throws Exception {
// 创建2000个随机数组成的数组:
long[] array = new long[2000];
long expectedSum = 0;
for (int i = 0; i < array.length; i++) {
array[i] = random();
expectedSum += array[i];
}
System.out.println("Expected sum: " + expectedSum);
// fork/join:
ForkJoinTask<Long> task = new SumTask(array, 0, array.length);
long startTime = System.currentTimeMillis();
Long result = ForkJoinPool.commonPool().invoke(task);
long endTime = System.currentTimeMillis();
System.out.println("Fork/join sum: " + result + " in " + (endTime - startTime) + " ms.");
}
static Random random = new Random(0);
static long random() {
return random.nextInt(10000);
}
}
class SumTask extends RecursiveTask<Long> {
static final int THRESHOLD = 500;
long[] array;
int start;
int end;
SumTask(long[] array, int start, int end) {
this.array = array;
this.start = start;
this.end = end;
}
@Override
protected Long compute() {
if (end - start <= THRESHOLD) {
// 如果任务足够小,直接计算:
long sum = 0;
for (int i = start; i < end; i++) {
sum += this.array[i];
// 故意放慢计算速度:
try {
Thread.sleep(1);
} catch (InterruptedException e) {
}
}
return sum;
}
// 任务太大,一分为二:
int middle = (end + start) / 2;
System.out.println(String.format("split %d~%d ==> %d~%d, %d~%d", start, end, start, middle, middle, end));
SumTask subtask1 = new SumTask(this.array, start, middle);
SumTask subtask2 = new SumTask(this.array, middle, end);
invokeAll(subtask1, subtask2);
Long subresult1 = subtask1.join();
Long subresult2 = subtask2.join();
Long result = subresult1 + subresult2;
System.out.println("result = " + subresult1 + " + " + subresult2 + " ==> " + result);
return result;
}
}
来自于:https://www.liaoxuefeng.com/wiki/1252599548343744/1306581226487842