forkjoin原理_java forkjoinpool

import com.google.common.base.Joiner;
import com.google.common.base.Splitter;
import org.apache.commons.lang3.RandomUtils;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;
/** * 一个数组内有10万个30左右的数值（非零），要求计算这些值的乘积。 * 时间要求：2s * 堆内存大小：4m * <p> * 实现方案：通过ForkJoin实现。 */
public class ForkJoinMultiply extends RecursiveTask<BigInteger> {
private int[] numbers;
private static final int THREASHOLD = 10000;
private static final int MAX_SIZE = 100000;
public ForkJoinMultiply(int[] numbers) {
this.numbers = numbers;
}
@Override
protected BigInteger compute() {
if(numbers.length<=THREASHOLD){
//如果数组容量小于阈值，直接计算乘积。
BigInteger result = BigInteger.ONE;
for(int i = 0;i<numbers.length;i++){
result = result.multiply(new BigInteger(String.valueOf(numbers[i])));
}
return result;
}else {
//如果容量大于阈值，则分组计算。分成两组
int middle = numbers.length/2;
int[] left = Arrays.copyOfRange(numbers,0,middle);
int[] right = Arrays.copyOfRange(numbers,middle,numbers.length);
ForkJoinMultiply leftTask = new ForkJoinMultiply(left);
ForkJoinMultiply rightTask = new ForkJoinMultiply(right);
leftTask.fork();
rightTask.fork();
return leftTask.join().multiply(rightTask.join());
}
}
public static void main(String[] args) {
long start = System.currentTimeMillis();
BigInteger temp = BigInteger.ONE;
int[] numbers = new int[MAX_SIZE];
for(int i = 0;i<MAX_SIZE;i++){
int randomNumber = RandomUtils.nextInt(20,40);
temp = temp.multiply(BigInteger.valueOf(randomNumber));
numbers[i] = randomNumber;
}
System.out.println("multiply result is "+temp+", cost time "+(System.currentTimeMillis()-start));
start = System.currentTimeMillis();
// 执行ForkJoin需要用到ForkJoinPool，调用commonPool方法是JDK1.8的实现
ForkJoinPool forkJoinPool = ForkJoinPool.commonPool();
ForkJoinMultiply multiply = new ForkJoinMultiply(numbers);
BigInteger result = forkJoinPool.invoke(multiply);
System.out.println("forkjoin multiply result is "+result+", cost time "+(System.currentTimeMillis()-start));
}
}