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RxJava2 源码分析二

2023-01-21 19:48:24

文章目录

  • 前言
  • RxJava2 线程调度
  • RxJava2 怎么进行线程调度
  • 总结

前言

经过RxJava2源码分析一,我们了解了RxJava2是怎么进行数据的发送和接收。那么这次我们主要是来分析,RxJava2是如何进行线程调度的。

RxJava2 线程调度

我们知道线程的调度还是很关键的,因为如果正常情况下,android给我们提供的方式是通过Hadler机制来进行线程间通信的,当了解了RxJava2,我们就多了一种通信方式,而且它进行线程间的切换是更加简洁的。

直接通过链式调用,就解决了线程间的切换

RxJava2 怎么进行线程调度

1、线程调度 subscribeOn
subscribeOn这里会指定Observable的调度器,也就是指定事件产生的线程。比如我们的事件是emitter.onNext(“1”); 那么指定到哪个线程呢,这里我们指定到 Schedulers .io
Schedulers .io( )默认是一个CachedThreadScheduler,很像一个有线程缓存的新线程调度器,这里把它理解成一个IO线程就可以了

Observable.create(new ObservableOnSubscribe<String>() {
           @Override
           public void subscribe(ObservableEmitter<String> emitter) throws Exception {
               emitter.onNext("1");//发送消息,事件产生的地方
               emitter.onComplete();
               Log.e(TAG, "subscribe called with: e = [" + emitter + "]" + Thread.currentThread());
           }
       }).subscribeOn(Schedulers.io())
               .map(new Function<String, String>() {//这里加了一个map操作符,主要是看事件处理所在的线程
           @Override
           public String apply(String s) throws Exception {
               Log.e(TAG, "apply() called with: s = [" + s + "]" + Thread.currentThread());
               return s;
           }
       })
               .subscribeOn(Schedulers.computation())
               .subscribe(new Observer<String>() {
           @Override
           public void onSubscribe(Disposable d) {
               Log.e(TAG,"onSubscribe() d=" + d );
           }

           @Override
           public void onNext(String s) {
               Log.e(TAG,"onNext() s=" + s );
           }

           @Override
           public void onError(Throwable e) {
               Log.e(TAG,"onError() e=" + e );
           }

           @Override
           public void onComplete() {
               Log.e(TAG,"onComplete() " );
               Log.e(TAG, "onComplete() called with:线程:" + Thread.currentThread());
           }
       });

我进到subscribeOn 去查看里面的实现
Observable#subscribeOn

    public final Observable<T> subscribeOn(Scheduler scheduler) {
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new ObservableSubscribeOn<T>(this, scheduler));//主要部分
    }

继续看 ObservableSubscribeOn
ObservableSubscribeOn #subscribeActual

    @Override
    public void subscribeActual(final Observer<? super T> observer) {
        final SubscribeOnObserver<T> parent = new SubscribeOnObserver<T>(observer);
        observer.onSubscribe(parent);
        parent.setDisposable(scheduler.scheduleDirect(new SubscribeTask(parent))); //主要部分
    }

ObservableSubscribeOn#SubscribeTask

final class SubscribeTask implements Runnable {
        private final SubscribeOnObserver<T> parent;

        SubscribeTask(SubscribeOnObserver<T> parent) {
            this.parent = parent;
        }

        @Override
        public void run() {
            source.subscribe(parent);//被观察者subscribe 观察者,这部分的任务已经被切换到子线程中了
        }
    }

SunscribeTask 实现了Runnable,我们看到source.subscribe(parent); 这一步,是完成订阅,而这部分内容是在子线程中处理的,这个时候parent是SubscribeOnObserver

我们看一下SubscribeOnObserver的实现

static final class SubscribeOnObserver<T> extends AtomicReference<Disposable> implements Observer<T>, Disposable {
...
       SubscribeOnObserver(Observer<? super T> downstream) {
            this.downstream = downstream;
            this.upstream = new AtomicReference<Disposable>();
        }
        @Override
        public void onNext(T t) {
            downstream.onNext(t);//new Observer中的onNext被调用了
        }

        @Override
        public void onError(Throwable t) {
            downstream.onError(t);//new Observer中的onError被调用了
        }

        @Override
        public void onComplete() {
            downstream.onComplete();//new Observer中的onComplete被调用了
        }

        @Override
        public void dispose() {
            DisposableHelper.dispose(upstream);
            DisposableHelper.dispose(this);
        }
...
    }

看代码中的注释,我们发现完成了new Observer 那几个方法的调用onNext,onError,onComplete。也就在那几个方法中可以接收消息。不同的是这部分内容是在指定的IO线程中进行的。

//接上前面的内容
 parent.setDisposable(scheduler.scheduleDirect(new SubscribeTask(parent)));

看完SunscribeTask 继续看scheduleDirect
Scheduler#scheduleDirect

 public Disposable scheduleDirect(@NonNull Runnable run) {
        return scheduleDirect(run, 0L, TimeUnit.NANOSECONDS);
    }

Scheduler#scheduleDirect

    public Disposable scheduleDirect(@NonNull Runnable run, long delay, @NonNull TimeUnit unit) {
        final Worker w = createWorker();

        final Runnable decoratedRun = RxJavaPlugins.onSchedule(run);

        DisposeTask task = new DisposeTask(decoratedRun, w);

        w.schedule(task, delay, unit);//开始执行任务

        return task;
    }

w.schedule(task, delay, unit); 这是最关键部分,在Worker的线程开始执行任务

顺便我们看下DisposeTask,其实它主要是对之前的任务进行包装,以便后面可以方便的取消线程任务,Disposable#dispose(用它取消任务)

static final class DisposeTask implements Disposable, Runnable, SchedulerRunnableIntrospection {
...
        DisposeTask(@NonNull Runnable decoratedRun, @NonNull Worker w) {
            this.decoratedRun = decoratedRun;
            this.w = w;
        }

        @Override
        public void run() {
            runner = Thread.currentThread();
            try {
                decoratedRun.run();  //任务执行
            } finally {
                dispose();
                runner = null;
            }
        }
     ...
    }

最终我们看下我们的代码执行的结果:

apply() called with: s = [1]Thread[RxCachedThreadScheduler-1,5,main]
onComplete() called with:线程:Thread[RxCachedThreadScheduler-1,5,main]
subscribe() called with: e = [CreateEmitter{DISPOSED}]Thread[RxCachedThreadScheduler-1,5,main]

你可能会问 onComplete()怎么也在IO线程呢,因为我们没有指定Observer在哪里执行,这是接下来要讲的。

2、线程调度 observeOn
observeOn指定observer将会在哪个Scheduler观察这个Observable.
具体点就是:ObserveOn 指定观察者的onNext, onError和onCompleted方法在哪个线程被执行

这次我们增加observeOn(AndroidSchedulers.mainThread())

Observable.create(new ObservableOnSubscribe<String>() {
            @Override
            public void subscribe(ObservableEmitter<String> emitter) throws Exception {
                emitter.onNext("1");
                emitter.onComplete();
                Log.e(TAG, "subscribe() called with: e = [" + emitter + "]" + Thread.currentThread());
            }
        }).subscribeOn(Schedulers.io())
                .map(new Function<String, String>() {
                    @Override
                    public String apply(String s) throws Exception {
                        //依然是io线程
                        Log.e(TAG, "apply() called with: s = [" + s + "]" + Thread.currentThread());
                        return s;
                    }
                })
                .observeOn(AndroidSchedulers.mainThread())//新增加部分
                .subscribe(new Observer<String>() {
                    @Override
                    public void onSubscribe(Disposable d) {
                        Log.e(TAG,"onSubscribe() d=" + d );
                    }

                    @Override
                    public void onNext(String s) {
                        Log.e(TAG,"onNext() s=" + s );
                    }

                    @Override
                    public void onError(Throwable e) {
                        Log.e(TAG,"onError() e=" + e );
                    }

                    @Override
                    public void onComplete() {
                        Log.e(TAG,"onComplete() " );
                        Log.e(TAG, "onComplete() called with:线程:" + Thread.currentThread());
                    }
                });

我们去看observeOn的实现
Observable#observeOn

    public final Observable<T> observeOn(Scheduler scheduler) {
        return observeOn(scheduler, false, bufferSize());
    }

继续看observeOn

   public final Observable<T> observeOn(Scheduler scheduler, boolean delayError, int bufferSize) {
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
        return RxJavaPlugins.onAssembly(new ObservableObserveOn<T>(this, scheduler, delayError, bufferSize));//关键部分
    }

接下来我们看ObservableObserveOn
ObservableObserveOn #ObservableObserveOn

    public ObservableObserveOn(ObservableSource<T> source, Scheduler scheduler, boolean delayError, int bufferSize) {
        super(source);
        this.scheduler = scheduler;//它就是AndroidSchedulers.mainThread()
        this.delayError = delayError;
        this.bufferSize = bufferSize;
    }

ObservableObserveOn #subscribeActual

  @Override
    protected void subscribeActual(Observer<? super T> observer) {
        if (scheduler instanceof TrampolineScheduler) {
            source.subscribe(observer);
        } else {
            Scheduler.Worker w = scheduler.createWorker();//scheduler就是上面的AndroidSchedulers.mainThread()

            source.subscribe(new ObserveOnObserver<T>(observer, w, delayError, bufferSize));  //主要部分
        }
    }

这里我们主要看ObserveOnObserver的实现
ObserveOnObserver#schedule

static final class ObserveOnObserver<T> extends BasicIntQueueDisposable<T>
    implements Observer<T>, Runnable {

    void schedule() {
            if (getAndIncrement() == 0) {
                worker.schedule(this);//this就是当前的ObserveOnObserver,它实现了Runnable,这把它放到了AndroidSchedulers.mainThread()创建的work 中处理
            }
        }
}

通过上面我们知道,worker.schedule(this) 把当前任务切换到了主线程中

 apply() called with: s = [1]Thread[RxCachedThreadScheduler-1,5,main]
 subscribe() called with: e = [CreateEmitter{DISPOSED}]Thread[RxCachedThreadScheduler-1,5,main]
 onComplete() called with:线程:Thread[main,5,main]

从日志中,我们能看到onComplete也确实已经被切换到了主线程中执行。

总结

  • 我们看到了Observable主要是通过subscribeOn来指定被观察者事件处理所在的线程
  • Observer 主要是通过observeOn 来指定观察者的事件处理所在的线程
  • 都会在源码中做相应的转换

如果对你有一点点帮助,那是值得高兴的事情。:)

我的csdn:http://blog.csdn.net/shenshizhong
我的简书:http://www.jianshu.com/u/345daf0211ad.、