大部分的操作及代码都在我上一篇博客中,这一篇我就其中比较蛋疼的问题说一下
1. Observable.interval()不起作用的解决办法
在Eclipse下测试Rxjava中的操作符interval()时出现了很奇怪的问题,怎么试都不能执行。
原因是我们的操作不是阻塞的:我们创建了一个每隔一段时间就发射数据的 Observable,然后我们注册了一个 Subscriber 来打印收到的数据。这两个操作都是非阻塞的,而 发射数据的计时器是运行在另外一个线程的,但是这个线程不会阻止 JVM 结束当前的程序,所以 如果没有 System.in.read(); 这个阻塞操作,还没发射数据则程序就已经结束运行了。
Observable.interval(1, TimeUnit.SECONDS)
.subscribe(new Subscriber<Long>() {
@Override
public void onCompleted() {
// TODO Auto-generated method stub
System.out.println("onCompleted ");
}
@Override
public void onError(Throwable arg0) {
// TODO Auto-generated method stub
}
@Override
public void onNext(Long arg0) {
// TODO Auto-generated method stub
System.out.println("onNext " + arg0);
}
});
这段代码在Eclipse下面运行没有达到我们预期的每隔一秒输出一个数字的结果。
怎么解决呢?
去官网找了下原因,也找到了解决方案:
https://github.com/ReactiveX/RxJava/issues/3932
Observable.interval(1, TimeUnit.SECONDS)
.subscribe(new Subscriber<Long>() {
@Override
public void onCompleted() {
// TODO Auto-generated method stub
System.out.println("onCompleted ");
}
@Override
public void onError(Throwable arg0) {
// TODO Auto-generated method stub
}
@Override
public void onNext(Long arg0) {
// TODO Auto-generated method stub
System.out.println("onNext " + arg0);
}
});
try {
Thread.sleep(20000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
这样就能输出结果了如下所示:
onNext 0
onNext 1
onNext 2
onNext 3
onNext 4
onNext 5
onNext 6
......
让程序沉睡一段时间似乎也不是很完美的解决方案,继续找就找到了如下的解决办法(https://github.com/ReactiveX/RxJava/issues/4132)。
具体原因如下:
When you use the default scheduler (Schedulers.computation()) the observable emits on another thread. If your program exits just after the subscribe then the observable is not given a chance to run. Put in a long sleep just after the subscribe() call and you will see it working.
Observable.interval(1, TimeUnit.SECONDS, Schedulers.trampoline())
.subscribe(new Subscriber<Long>() {
@Override
public void onCompleted() {
// TODO Auto-generated method stub
System.out.println("onCompleted ");
}
@Override
public void onError(Throwable arg0) {
// TODO Auto-generated method stub
}
@Override
public void onNext(Long arg0) {
// TODO Auto-generated method stub
System.out.println("onNext " + arg0);
}
});
需要注意的是,上面代码中的 Schedulers.trampoline()替换为Schedulers.immediate()也是可以运行的,但是这样做是不安全的。
The immediate() scheduler is not safe for recursive scheduling on the current thread, use trampoline() instead.
Schedulers.computation() 与 Schedulers.trampoline()区别
/**
* Creates and returns a {@link Scheduler} that executes work immediately on the current thread.
*
* @return a {@link Scheduler} that executes work immediately
*/
public static Scheduler immediate() {
return rx.internal.schedulers.ImmediateScheduler.INSTANCE;
}
/**
* Creates and returns a {@link Scheduler} that queues work on the current thread to be executed after the
* current work completes.
*
* @return a {@link Scheduler} that queues work on the current thread
*/
public static Scheduler trampoline() {
return rx.internal.schedulers.TrampolineScheduler.INSTANCE;
}
从上面源码可以看出,immediate()方法返回的是ImmediateScheduler类的实例,而trampoline()方法返回的是TrampolineScheduler类的实例。
ImmediateScheduler类的部分源码:
/**
* Executes work immediately on the current thread.
*/
public final class ImmediateScheduler extends Scheduler {
public static final ImmediateScheduler INSTANCE = new ImmediateScheduler();
private ImmediateScheduler() {
// the class is singleton
}
从ImmediateScheduler类的官网介绍中可以看出ImmediateScheduler执行在当前main线程。
TrampolineScheduler类的部分源码:
/**
* Schedules work on the current thread but does not execute immediately. Work is put in a queue and executed
* after the current unit of work is completed.
*/
public final class TrampolineScheduler extends Scheduler {
public static final TrampolineScheduler INSTANCE = new TrampolineScheduler();
@Override
public Worker createWorker() {
return new InnerCurrentThreadScheduler();
}
从TrampolineScheduler
类的官网介绍中可以看出TrampolineScheduler
不会立即执行,当其他排队任务介绍时才执行,当然TrampolineScheduler
运行在当前main线程。