我有以下代码：

public class Main {
    public static void main(String[] args) {
        ExecutorService executorService = Executors.newWorkStealingPool(1);
        ForkJoinPool workStealingPool = (ForkJoinPool)executorService;
        RecursiveRunnable recursiveRunnable = new RecursiveRunnable(5);
        workStealingPool.invoke(recursiveRunnable);
    }
}
public class RecursiveRunnable extends Recursivetask<Integer> implements Runnable {
    private final int n;

    public RecursiveRunnable(int n) {
        this.n = n;
    }

    @Override
    @sneakyThrows
    protected Integer compute() {
        Thread thread = Thread.currentThread();
        System.out.println("Thread started,threadId=" + thread.getId() + " n=" + n +  " activeCount=" + Thread.activeCount());
        if (n <= 1) {
            return n;
        }
        RecursiveRunnable f1 = new RecursiveRunnable(n - 1);
        f1.fork();
        RecursiveRunnable f2 = new RecursiveRunnable(n - 2);
        f2.fork();
        int result = 0;
        result = f2.get() + f1.get();
        System.out.println("Thread finished,threadId=" + thread.getId() + " n=" + n +  " activeCount=" + Thread.activeCount() + " result=" + result);
        return result;
    }

    @Override
    public void run() {
        compute();
    }
}

我希望代码不会在 fork（） 语句中打开新线程，
因为并行度为1 。
但是这段代码的输出是：

  

线程已启动，threadId = 11 n = 5 activeCount = 3
线程已启动，   threadId = 11 n = 3 activeCount = 3
线程已启动，threadId = 11 n = 1   activeCount = 3
线程已启动，threadId = 11 n = 2 activeCount = 3   
线程已启动，threadId = 11 n = 0 activeCount = 3
线程   开始，threadId = 11 n = 1 activeCount = 3
线程完成，   threadId = 11 n = 2 activeCount = 3结果= 1
线程完成，   threadId = 11 n = 3 activeCount = 3 result = 2
线程已启动，   threadId = 11 n = 4 activeCount = 3
线程已启动，threadId = 11 n = 2   activeCount = 3
线程已启动，threadId = 11 n = 0 activeCount = 3   
线程已启动，threadId = 11 n = 1 activeCount = 3
线程   完成，threadId = 11 n = 2 activeCount = 3结果= 1
线程   已启动，threadId = 11 n = 3 activeCount = 3
线程已启动，   threadId = 11 n = 1 activeCount = 3
线程已启动，threadId = 11 n = 2   activeCount = 3
线程已启动，threadId = 11 n = 0 activeCount = 3   
线程已启动，threadId = 11 n = 1 activeCount = 3
线程   完成，threadId = 11 n = 2 activeCount = 3结果= 1
线程   完成，threadId = 11 n = 3 activeCount = 3结果= 2
线程   完成，threadId = 11 n = 4 activeCount = 3 result = 3
线程   完成，threadId = 11 n = 5 activeCount = 3 result = 5

从输出打印中可以看到，我们一次有12个线程处于活动状态。
尽管 parallelism为1 ，如何打开新线程？