Android开源库——RxJava和RxAndroid

RxJava和RxAndroid是什么？

RxJava是基于JVM的响应式扩展，用于编写异步代码

RxAndroid是关于Android的RxJava绑定

RxJava和RxAndroid使用

依赖

implementation 'io.reactivex.rxjava3:rxjava:3.1.0'
implementation 'io.reactivex.rxjava3:rxandroid:3.0.2'

使用过程

如下模拟在子线程中进行耗时操作，并将结果返回到主线程中处理

• Flowable：将要进行的操作
• subscribeOn()：操作要运行的线程
• observeOn() ：处理结果要运行的线程
• subscribe()：处理结果

Flowable.fromCallable(() -> {
            Thread.sleep(1000);
            return "Done";
        })
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(System.out::println, Throwable::printStackTrace);

Flowable<String> source = Flowable.fromCallable(() -> {
    Thread.sleep(1000); 
    return "Done";
});
Flowable<String> runBackground = source.subscribeOn(Schedulers.io());
Flowable<String> showForeground = runBackground.observeOn(AndroidSchedulers.mainThread());
showForeground.subscribe(System.out::println, Throwable::printStackTrace);

RxJava源码解析

Publisher

Publisher用于发布数据，Subscriber通过subscribe()订阅数据

public interface Publisher<T> {
    public void subscribe(Subscriber<? super T> s);
}

Subscriber

Subscriber接收Publisher发布的数据

• onSubscribe()：subscribe()回调函数，回调前会创建Subscription用于控制数据发布和停止
• onNext()：当Subscription调用request()时会调用onNext()发布数据
• onError()：处理接收到的错误
• onComplete()：处理完成的情况

public interface Subscriber<T> {

    public void onSubscribe(Subscription s);

    public void onNext(T t);

    public void onError(Throwable t);

    public void onComplete();
}

Subscription

Subscription表示Publisher和Subscriber的对应关系

• request()：向Publisher请求数据
• cancel()：让Publisher停止发布数据

public interface Subscription {

    public void request(long n);

    public void cancel();
}

Scheduler

createWorker()用于创建Worker ，具体的调度工作由Worker的schedule()完成

public abstract class Scheduler {
	public abstract Worker createWorker();

    public abstract static class Worker implements Disposable {

        @NonNull
        public Disposable schedule(@NonNull Runnable run) {
            return schedule(run, 0L, TimeUnit.NANOSECONDS);
        }
        
        public abstract Disposable schedule(@NonNull Runnable run, long delay, @NonNull TimeUnit unit);
   }
}

source传递过程

fromCallable()创建FlowableFromCallable，传递callable

public abstract class Flowable<@NonNull T> implements Publisher<T> {

    public static <@NonNull T> Flowable<T> fromCallable(@NonNull Callable<? extends T> callable) {
        return RxJavaPlugins.onAssembly(new FlowableFromCallable<>(callable));
    }
}

subscribeOn()创建FlowableSubscribeOn，传递this（即FlowableFromCallable）作为source

public abstract class Flowable<@NonNull T> implements Publisher<T> {

    public final Flowable<T> subscribeOn(@NonNull Scheduler scheduler) {
        Objects.requireNonNull(scheduler, "scheduler is null");
        return subscribeOn(scheduler, !(this instanceof FlowableCreate));
    }
    
    public final Flowable<T> subscribeOn(@NonNull Scheduler scheduler, boolean requestOn) {
        Objects.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new FlowableSubscribeOn<>(this, scheduler, requestOn));
    }
}

observeOn()创建FlowableObserveOn，传递this（即FlowableSubscribeOn）作为source

public abstract class Flowable<@NonNull T> implements Publisher<T> {

    public final Flowable<T> observeOn(@NonNull Scheduler scheduler) {
        return observeOn(scheduler, false, bufferSize());
    }
    
    public final Flowable<T> observeOn(@NonNull Scheduler scheduler, boolean delayError, int bufferSize) {
        Objects.requireNonNull(scheduler, "scheduler is null");
        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
        return RxJavaPlugins.onAssembly(new FlowableObserveOn<>(this, scheduler, delayError, bufferSize));
    }
}

即依次将自身当作Flowable，作为参数source传递给下一个Flowable

subscribe()流程

subscribe()最终调用具体Flowable的subscribeActual()

public abstract class Flowable<@NonNull T> implements Publisher<T> {
	......
    public final Disposable subscribe(@NonNull Consumer<? super T> onNext, @NonNull Consumer<? super Throwable> onError) {
        return subscribe(onNext, onError, Functions.EMPTY_ACTION);
    }
    
    public final Disposable subscribe(@NonNull Consumer<? super T> onNext, @NonNull Consumer<? super Throwable> onError,
            @NonNull Action onComplete) {
		.....
        LambdaSubscriber<T> ls = new LambdaSubscriber<>(onNext, onError, onComplete, FlowableInternalHelper.RequestMax.INSTANCE);

        subscribe(ls);

        return ls;
    }
    
    public final void subscribe(@NonNull FlowableSubscriber<? super T> subscriber) {
        try {

            Subscriber<? super T> flowableSubscriber = RxJavaPlugins.onSubscribe(this, subscriber);
            ......
            subscribeActual(flowableSubscriber);
        }......
    }
    protected abstract void subscribeActual(@NonNull Subscriber<? super T> subscriber);
}

调用过程和传递过程是相反的，先调用FlowableObserveOn的subscribeActual()

public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {
	......
    @Override
    public void subscribeActual(Subscriber<? super T> s) {
        Worker worker = scheduler.createWorker();

        if (s instanceof ConditionalSubscriber) {
            .....
        } else {
            source.subscribe(new ObserveOnSubscriber<>(s, worker, delayError, prefetch));
        }
    }

}

上面的source就是上一层传递下来的FlowableSubscribeOn，即调用到FlowableSubscribeOn的subscribeActual()

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {

	......
    @Override
    public void subscribeActual(final Subscriber<? super T> s) {
        Scheduler.Worker w = scheduler.createWorker();
        final SubscribeOnSubscriber<T> sos = new SubscribeOnSubscriber<>(s, w, source, nonScheduledRequests);
        .....
        w.schedule(sos);
    }
    
    static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>
    implements FlowableSubscriber<T>, Subscription, Runnable {
		......
        @Override
        public void run() {
            lazySet(Thread.currentThread());
            Publisher<T> src = source;
            source = null;
            src.subscribe(this);
        }

schedule()最终会调用run()方法，lazySet()切换线程，上面的source就是上一层传递下来的FlowableFromCallable，即将到FlowableFromCallable的subscribeActual()放到指定线程中运行

public final class FlowableFromCallable<T> extends Flowable<T> implements Supplier<T> {
    final Callable<? extends T> callable;
    ......
    @Override
    public void subscribeActual(Subscriber<? super T> s) {
        DeferredScalarSubscription<T> deferred = new DeferredScalarSubscription<>(s);
        s.onSubscribe(deferred);

        T t;
        try {
            t = Objects.requireNonNull(callable.call(), "The callable returned a null value");
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            if (deferred.isCancelled()) {
                RxJavaPlugins.onError(ex);
            } else {
                s.onError(ex);
            }
            return;
        }

        deferred.complete(t);
    }
    ......
}

上面若出错回调onError()，否则调用downstream的onNext()传递结果

public class DeferredScalarSubscription<@NonNull T> extends BasicIntQueueSubscription<T> {

    public final void complete(T v) {
        int state = get();
        for (;;) {
            ......
            if (state == HAS_REQUEST_NO_VALUE) {
                lazySet(HAS_REQUEST_HAS_VALUE);
                Subscriber<? super T> a = downstream;
                a.onNext(v);
                if (get() != CANCELLED) {
                    a.onComplete();
                }
                return;
            }
            value = v;
            ......
        }
    }
}

onNext()过程

调用FlowableSubscribeOn.SubscribeOnSubscriber的onNext()，调用downstream的onNext()传递结果

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {

    static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>
    implements FlowableSubscriber<T>, Subscription, Runnable {
    
        @Override
        public void onNext(T t) {
            downstream.onNext(t);
        }
    }
}

调用FlowableObserveOn.BaseObserveOnSubscriber的onNext()、trySchedule()，schedule()最终会调用run()方法，根据sourceMode判断是同步还是异步

• FlowableObserveOn.ObserveOnSubscriber的runSync()和runAsync()都调用downstream的onNext()传递结果

public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {
    .....
    abstract static class BaseObserveOnSubscriber<T>
    extends BasicIntQueueSubscription<T>
    implements FlowableSubscriber<T>, Runnable {
        @Override
        public final void onNext(T t) {
            ......
            trySchedule();
        }'
        
        final void trySchedule() {
            ......
            worker.schedule(this);
        }
        
        @Override
        public final void run() {
            if (outputFused) {
                runBackfused();
            } else if (sourceMode == SYNC) {
                runSync();
            } else {
                runAsync();
            }
        }
    }
    
    static final class ObserveOnSubscriber<T> extends BaseObserveOnSubscriber<T>
    implements FlowableSubscriber<T> {
        void runSync() {
			......
            final Subscriber<? super T> a = downstream;
			......
            for (;;) {
				......
                while (e != r) {
                    ......
                    a.onNext(v);
					......
                }......
            }
        }
    	.....
        @Override
        void runAsync() {

            final Subscriber<? super T> a = downstream;

            for (;;) {
            	......
                while (e != r) {
                    .....
                    a.onNext(v);
                    .....
                }
                .....
            }
        }
    }
}

调用LambdaSubscriber的onNext()，通过传入的Consumer消费掉最终的结果，即通过System.out::println打印出来

public final class LambdaSubscriber<T> extends AtomicReference<Subscription>
        implements FlowableSubscriber<T>, Subscription, Disposable, LambdaConsumerIntrospection {
	.....
    @Override
    public void onNext(T t) {
        if (!isDisposed()) {
            try {
                onNext.accept(t);
            } catch (Throwable e) {
                Exceptions.throwIfFatal(e);
                get().cancel();
                onError(e);
            }
        }
    }
}

onSubscribe()和request()流程

FlowableFromCallable回调下一层的onSubscribe()，其将Subscription存到upstream

public final class FlowableFromCallable<T> extends Flowable<T> implements Supplier<T> {
    final Callable<? extends T> callable;
    @Override
    public void subscribeActual(Subscriber<? super T> s) {
        DeferredScalarSubscription<T> deferred = new DeferredScalarSubscription<>(s);
        s.onSubscribe(deferred);
		......
    }
}

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {

    static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>
    implements FlowableSubscriber<T>, Subscription, Runnable {
        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.setOnce(this.upstream, s)) {
                ......
            }
        }
     }
}

FlowableSubscribeOn回调下一层的onSubscribe()，其回调下一层的onSubscribe()和上一层的request()请求数据

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {
	......
    @Override
    public void subscribeActual(final Subscriber<? super T> s) {
        Scheduler.Worker w = scheduler.createWorker();
        final SubscribeOnSubscriber<T> sos = new SubscribeOnSubscriber<>(s, w, source, nonScheduledRequests);
        s.onSubscribe(sos);
    }   
}

public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {
    
    static final class ObserveOnSubscriber<T> extends BaseObserveOnSubscriber<T>
    implements FlowableSubscriber<T> {
        ......
        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(this.upstream, s)) {
                this.upstream = s;
				......
                queue = new SpscArrayQueue<>(prefetch);

                downstream.onSubscribe(this);

                s.request(prefetch);
            }
        }
    }
}

LambdaSubscriber利用FlowableInternalHelper.RequestMax的accept()调用上一层的request()，从schedule()获取数据

public final class LambdaSubscriber<T> extends AtomicReference<Subscription>
        implements FlowableSubscriber<T>, Subscription, Disposable, LambdaConsumerIntrospection {
     @Override
    public void onSubscribe(Subscription s) {
        if (SubscriptionHelper.setOnce(this, s)) {
            try {
                onSubscribe.accept(this);
            } catch (Throwable ex) {
                ......
            }
        }
    }
 }
 
public final class FlowableInternalHelper {
	    public enum RequestMax implements Consumer<Subscription> {
        INSTANCE;
        @Override
        public void accept(Subscription t) {
            t.request(Long.MAX_VALUE);
        }
    }
}

public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {

    abstract static class BaseObserveOnSubscriber<T>
    extends BasicIntQueueSubscription<T>
    implements FlowableSubscriber<T>, Runnable {
    
        @Override
        public final void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                BackpressureHelper.add(requested, n);
                trySchedule();
            }
        }
        
        final void trySchedule() {
            ......
            worker.schedule(this);
        }
	}
}

FlowableSubscribeOn.SubscribeOnSubscriber的request()、requestUpstream()判断当前线程，若未切换线程调用schedule()切换线程调用上一层的request()

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {
    static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>
    implements FlowableSubscriber<T>, Subscription, Runnable {
    
        @Override
        public void request(final long n) {
            if (SubscriptionHelper.validate(n)) {
                Subscription s = this.upstream.get();
                if (s != null) {
                    requestUpstream(n, s);
                } else {
                     ......
                    }
                }
            }
        }

        void requestUpstream(final long n, final Subscription s) {
            if (nonScheduledRequests || Thread.currentThread() == get()) {
                s.request(n);
            } else {
                worker.schedule(new Request(s, n));
            }
        }
        
        static final class Request implements Runnable {
            ......
            @Override
            public void run() {
                upstream.request(n);
            }
        }
	}
}

DeferredScalarSubscription接收到请求后，将值传给downstream的onNext()

public class DeferredScalarSubscription<@NonNull T> extends BasicIntQueueSubscription<T> {
    @Override
    public final void request(long n) {
        if (SubscriptionHelper.validate(n)) {
            for (;;) {
                int state = get();
                ......
                if (state == NO_REQUEST_HAS_VALUE) {
                    if (compareAndSet(NO_REQUEST_HAS_VALUE, HAS_REQUEST_HAS_VALUE)) {
                        T v = value;
                        if (v != null) {
                            value = null;
                            Subscriber<? super T> a = downstream;
                            a.onNext(v);
                            if (get() != CANCELLED) {
                                a.onComplete();
                            }
                        }
                    }
                    return;
                }
                ......
            }
        }
    }
}

Schedulers.io()调度过程

Schedulers.io() = Schedulers.IO = IOTask() = IoHolder.DEFAULT = IoScheduler()

public final class Schedulers {

	static final Scheduler IO;

    static final class IoHolder {
        static final Scheduler DEFAULT = new IoScheduler();
    }

    static {

        IO = RxJavaPlugins.initIoScheduler(new IOTask());

    }

    public static Scheduler io() {
        return RxJavaPlugins.onIoScheduler(IO);
    }

    static final class IOTask implements Supplier<Scheduler> {
        @Override
        public Scheduler get() {
            return IoHolder.DEFAULT;
        }
    }
}

FlowableSubscribeOn的subscribeActual()通过IoScheduler创建Worker并调用schedule()

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {
	......
    @Override
    public void subscribeActual(final Subscriber<? super T> s) {
        Scheduler.Worker w = scheduler.createWorker();
        final SubscribeOnSubscriber<T> sos = new SubscribeOnSubscriber<>(s, w, source, nonScheduledRequests);
       	.....
        w.schedule(sos);
    }
}

调用IoScheduler的createWorker()会返回EventLoopWorker

public final class IoScheduler extends Scheduler {

	@NonNull
    @Override
    public Worker createWorker() {
        return new EventLoopWorker(pool.get());
    }
}

调用IoScheduler.EventLoopWorker的schedule()最终调用ThreadWorker的父类NewThreadWorker的scheduleActual()

public final class IoScheduler extends Scheduler {
    static final class EventLoopWorker extends Scheduler.Worker implements Runnable {
        @NonNull
        @Override
        public Disposable schedule(@NonNull Runnable action, long delayTime, @NonNull TimeUnit unit) {
        	......
            return threadWorker.scheduleActual(action, delayTime, unit, tasks);
        }
    }
    static final class ThreadWorker extends NewThreadWorker {
		......
    }
}

调用scheduleActual()将Runnable封装成ScheduledRunnable，通过ScheduledThreadPoolExecutor的submit()或schedule()提交

public class NewThreadWorker extends Scheduler.Worker implements Disposable {

    private final ScheduledExecutorService executor;

    volatile boolean disposed;

    public NewThreadWorker(ThreadFactory threadFactory) {
        executor = SchedulerPoolFactory.create(threadFactory);
    }
    
    @NonNull
    public ScheduledRunnable scheduleActual(final Runnable run, long delayTime, @NonNull TimeUnit unit, @Nullable DisposableContainer parent) {
        Runnable decoratedRun = RxJavaPlugins.onSchedule(run);

        ScheduledRunnable sr = new ScheduledRunnable(decoratedRun, parent);
		......

        Future<?> f;
        try {
            if (delayTime <= 0) {
                f = executor.submit((Callable<Object>)sr);
            } else {
                f = executor.schedule((Callable<Object>)sr, delayTime, unit);
            }
            sr.setFuture(f);
        } catch (RejectedExecutionException ex) {
            ......
        }

        return sr;
    }
}

public final class SchedulerPoolFactory {
    public static ScheduledExecutorService create(ThreadFactory factory) {
        final ScheduledThreadPoolExecutor exec = new ScheduledThreadPoolExecutor(1, factory);
        exec.setRemoveOnCancelPolicy(PURGE_ENABLED);
        return exec;
    }
}

线程池会调用FlowableSubscribeOn.SubscribeOnSubscriber的run()方法，SubscribeOnSubscriber继承了AtomicReference<Thread>，lazySet()切换线程调用上一层source的subscribe()

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {
    static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>
    implements FlowableSubscriber<T>, Subscription, Runnable {
    
        @Override
        public void run() {
            lazySet(Thread.currentThread());
            Publisher<T> src = source;
            source = null;
            src.subscribe(this);
        }
    }

}

AndroidSchedulers.mainThread()调度过程

AndroidSchedulers.mainThread() = AndroidSchedulers.MAIN_THREAD = MainHolder.DEFAULT = HandlerScheduler()，通过主线程Looper创建handler

public final class AndroidSchedulers {

    private static final class MainHolder {
        static final Scheduler DEFAULT = internalFrom(Looper.getMainLooper(), true);
    }

    private static final Scheduler MAIN_THREAD =
        RxAndroidPlugins.initMainThreadScheduler(() -> MainHolder.DEFAULT);
	}
	
    public static Scheduler mainThread() {
        return RxAndroidPlugins.onMainThreadScheduler(MAIN_THREAD);
    }

    private static Scheduler internalFrom(Looper looper, boolean async) {
        ......
        return new HandlerScheduler(new Handler(looper), async);
    }
}

FlowableObserveOn的subscribeActual()通过IoScheduler创建Worker，在onNext()的trySchedule()调用schedule()

public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {
    @Override
    public void subscribeActual(Subscriber<? super T> s) {
        Worker worker = scheduler.createWorker();

        if (s instanceof ConditionalSubscriber) {
            ......
        } else {
            source.subscribe(new ObserveOnSubscriber<>(s, worker, delayError, prefetch));
        }
    }

	abstract static class BaseObserveOnSubscriber<T>
    extends BasicIntQueueSubscription<T>
    implements FlowableSubscriber<T>, Runnable {
        @Override
        public final void onNext(T t) {
            ......
            trySchedule();
        }
        
        final void trySchedule() {
            ......
            worker.schedule(this);
        }
    }
}

调用HandlerScheduler的createWorker()返回HandlerWorker()

final class HandlerScheduler extends Scheduler {
    @Override
    public Worker createWorker() {
        return new HandlerWorker(handler, async);
    }
}

调用HandlerScheduler.HandlerWorker的schedule()，将Runnable封装成ScheduledRunnable，调用主线程handler的sendMessageDelayed()

final class HandlerScheduler extends Scheduler {

    private static final class HandlerWorker extends Worker {
    
        @Override
        public Disposable schedule(Runnable run, long delay, TimeUnit unit) {
           	......
            run = RxJavaPlugins.onSchedule(run);

            ScheduledRunnable scheduled = new ScheduledRunnable(handler, run);

            Message message = Message.obtain(handler, scheduled);
            message.obj = this; 

            if (async) {
                message.setAsynchronous(true);
            }

            handler.sendMessageDelayed(message, unit.toMillis(delay));
            ......
            return scheduled;
        }
    }
}

最终主线程会调用FlowableObserveOn.BaseObserveOnSubscriber的run()，根据sourceMode判断是同步还是异步

• FlowableObserveOn.ObserveOnSubscriber的runSync()和runAsync()都调用downstream的onNext()传递结果

public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {
    .....
    abstract static class BaseObserveOnSubscriber<T>
    extends BasicIntQueueSubscription<T>
    implements FlowableSubscriber<T>, Runnable {
		......
        @Override
        public final void run() {
            if (outputFused) {
                runBackfused();
            } else if (sourceMode == SYNC) {
                runSync();
            } else {
                runAsync();
            }
        }
    }
    
    static final class ObserveOnSubscriber<T> extends BaseObserveOnSubscriber<T>
    implements FlowableSubscriber<T> {
        void runSync() {
			......
            final Subscriber<? super T> a = downstream;
			......
            for (;;) {
				......
                while (e != r) {
                    ......
                    a.onNext(v);
					......
                }......
            }
        }
    	.....
        @Override
        void runAsync() {

            final Subscriber<? super T> a = downstream;

            for (;;) {
            	......
                while (e != r) {
                    .....
                    a.onNext(v);
                    .....
                }
                .....
            }
        }
    }
}