RxJava - Why the executors only use one thread

Question

I have created a fixed thread-pool to process an event emit per 300 milliseconds and assume the process need 1000 millisecond. Suppose the multi-thread will work but only one thread reused.

If i set the sleepTime smaller than 300ms, the processing thread change, but that is useless.

Questions: What can I do to make it concurrent? Why the program reuse the thread?

Thank you in advance

public static void main(String[] args) throws InterruptedException {
    long sleepTime = 1000;
    ExecutorService e = Executors.newFixedThreadPool(3);

    Observable.interval(300, TimeUnit.MILLISECONDS)
    .subscribeOn(Schedulers.computation())
    .flatMap(new Func1<Long, Observable<Long>>() {
        @Override
        public Observable<Long> call(Long pT) {
            return Observable.just(pT).subscribeOn(Schedulers.from(e));
        }
    })
    .doOnNext(new Action1<Long>() {

        @Override
        public void call(Long pT) {
            try {
                Thread.sleep(sleepTime);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
    })
    .subscribe(new Action1<Long>() {

        @Override
        public void call(Long pT) {
            System.out.println("i am " + pT + "in thread:" + Thread.currentThread().getName());

        }
    });


    Thread.sleep(50000);
    e.shutdownNow();

}

Logs

i am 0in thread:pool-1-thread-1
i am 1in thread:pool-1-thread-1
i am 2in thread:pool-1-thread-1
i am 3in thread:pool-1-thread-1
i am 4in thread:pool-1-thread-1
i am 5in thread:pool-1-thread-1
i am 6in thread:pool-1-thread-1
i am 7in thread:pool-1-thread-1
i am 8in thread:pool-1-thread-1
i am 9in thread:pool-1-thread-1
i am 10in thread:pool-1-thread-1
i am 11in thread:pool-1-thread-1

Answer 1

I found the answer in GitHub!

The inner observable did emit on multi-thread, but the follow do on next is not. If I want it parallel, I should do it in the inner observable .