Parallel stream
Fork and join
Pseudocode
If(task is small enough or no longer divisible){
Compute task sequentially
}else{
split task in two subtasks
call this method recursively possibly further splitting each subtask
wait for the completion of all subtasks
combine the results of each subtask}
public class ForkJoinSumCalculator extends RecursiveTask<Long> {
private final long[] numbers;
private final int start;
private final int end;
public static final long THRESHOLD = 10_1000;
public ForkJoinSumCalculator(long[] numbers) {
this(numbers, 0, numbers.length);
}
public ForkJoinSumCalculator(long[] numbers, int start, int end) {
this.numbers = numbers;
this.start = start;
this.end = end;
}
@Override
protected Long compute() {
int length = end - start;
if (length <= THRESHOLD) {
return computeSequentially();
}
ForkJoinSumCalculator leftTask = new ForkJoinSumCalculator(numbers, start, start + length / 2);
leftTask.fork();
ForkJoinSumCalculator rightTask = new ForkJoinSumCalculator(numbers, start + length / 2, end);
Long rightResult = rightTask.compute();
Long leftResult = leftTask.join();
return leftResult + rightResult;
}
private long computeSequentially() {
long sum = 0;
for (int i = start; i < end; i++) {
sum += numbers[i];
}
return sum;
}
public static long forkJoinSum(long n){
long[] numbers= LongStream.rangeClosed(1,n).toArray();
ForkJoinTask<Long> task=new ForkJoinSumCalculator(numbers);
return new ForkJoinPool().invoke(task);
}
}
@Test
public void test(){
long i = 10000000;
StopWatch stopWatch=new StopWatch();
stopWatch.start();
Function<Long,Long> adder=ForkJoinSumCalculator::forkJoinSum ;
adder.apply(i);
stopWatch.stop();
System.out.println(stopWatch.getTotalTimeSeconds());
}
来源：oschina
链接：https://my.oschina.net/u/1866807/blog/1838391