上一篇描述了如何走到observer的onNext方法，下面加上进程调度，再来看看如何调度的
var sources = object : ObservableOnSubscribe<String> {
override fun subscribe(emitter: ObservableEmitter<String>) {
emitter.onNext("下一步")
emitter.onComplete()
}
}
var observable = Observable.create(sources)
var observable1 = observable.subscribeOn(Schedulers.io())
var observable2 = observable1.observeOn(AndroidSchedulers.mainThread())
var observer = object :Observer<String>{
override fun onComplete() {
}
override fun onSubscribe(d: Disposable) {
}
override fun onNext(t: String) {
}
override fun onError(e: Throwable) {
}
}
observable2.subscribe(observer)
前面已经分析了observable的创建过程，下面来分析observable1的创建过程，也就是observable.subscribeOn(Schedulers.io())干了什么，通过前面的分析知道observable就是ObservableCreate对象，但是ObservableCreate中没有subscribeOn方法，所以到父类中找
public final Observable<T> subscribeOn(Scheduler scheduler) {
//判断scheduler是否为null
ObjectHelper.requireNonNull(scheduler, "scheduler is null");
//判断onObservableAssembly是否为null
//第一次默认为null，所以返回的是ObservableSubscribeOn
return RxJavaPlugins.onAssembly(new ObservableSubscribeOn<T>(this, scheduler));
}
所以observable1就是一个ObservableSubscribeOn对象，里面保存有observable和scheduler，所以当这时不考虑observeOn(AndroidSchedulers.mainThread())，这一段代时，直接调用observable1.subscribe(observer)是，就像下面这样
var sources = object : ObservableOnSubscribe<String> {
override fun subscribe(emitter: ObservableEmitter<String>) {
emitter.onNext("下一步")
emitter.onComplete()
}
}
var observable = Observable.create(sources)
var observable1 = observable.subscribeOn(Schedulers.io())
// var observable2 = observable1.observeOn(AndroidSchedulers.mainThread())
var observer = object : Observer<String> {
override fun onComplete() {
}
override fun onSubscribe(d: Disposable) {
}
override fun onNext(t: String) {
}
override fun onError(e: Throwable) {
}
}
observable1.subscribe(observer)
通过前面分析，当调用observable1.subscribe(observer)时，就会回调到ObservableSubscribeOn的subscribeActual方法中
//ObservableSubscribeOn 的subscribeActual方法
public void subscribeActual(final Observer<? super T> observer) {
//创建SubscribeOnObserver对象
final SubscribeOnObserver<T> parent = new SubscribeOnObserver<T>(observer);
//调用observer的onSubscribe方法
observer.onSubscribe(parent);
//重要的是括号里面的内容
parent.setDisposable(scheduler.scheduleDirect(new SubscribeTask(parent)));
}
到上面，重要的是scheduler.scheduleDirect(new SubscribeTask(parent))这一句代码，其中scheduler是Schedulers.io()返回的对象，SubscribeTask是一个实现Runnable的接口，先来看scheduler.scheduleDirect()方法做了什么
public Disposable scheduleDirect(@NonNull Runnable run) {
return scheduleDirect(run, 0L, TimeUnit.NANOSECONDS);
}
public Disposable scheduleDirect(@NonNull Runnable run, long delay, @NonNull TimeUnit unit) {
//创建一个Worker
final Worker w = createWorker();
//判断onScheduleHandler是否为null，默认为null，所以返回自身
//这里的run就是前面的SubscribeTask
final Runnable decoratedRun = RxJavaPlugins.onSchedule(run);
//创建DisposeTask，将Worker 和SubscribeTask传进去
//DisposeTask实现了Runnable
DisposeTask task = new DisposeTask(decoratedRun, w);
//调用schedule方法
w.schedule(task, delay, unit);
//返回task
return task;
}
createWorker()是一个抽象方法，所以要看scheduler的实例对象，看Schedulers.io()返回什么
public static Scheduler io() {
//判断onIoHandler是否为null默认为null，所以返回IO
return RxJavaPlugins.onIoScheduler(IO);
}
所以看IO是什么
public final class Schedulers {
@NonNull
static final Scheduler IO;
//...
static final class IoHolder {
static final Scheduler DEFAULT = new IoScheduler();
}
//...
static {
//....
IO = RxJavaPlugins.initIoScheduler(new IOTask());
}
}
RxJavaPlugins.initIoScheduler(new IOTask())这一段代码最后会调用IOTask.call 方法
static final class IOTask implements Callable<Scheduler> {
@Override
public Scheduler call() throws Exception {
return IoHolder.DEFAULT;
}
}
最后又会回调到IoHolder.DEFAULT中，所以最后返回的就是IoScheduler对象，
来看IoScheduler的构造方法做了什么
public IoScheduler() {
//调用自身WORKER_THREAD_FACTORY是在static初始化的
this(WORKER_THREAD_FACTORY);
}
public IoScheduler(ThreadFactory threadFactory) {
//将threadFactory赋值
this.threadFactory = threadFactory;
//创建AtomicReference，用来持有CachedWorkerPool的引用
this.pool = new AtomicReference<CachedWorkerPool>(NONE);
//调用start方法
start();
}
@Override
public void start() {
//创建CachedWorkerPool
CachedWorkerPool update = new CachedWorkerPool(KEEP_ALIVE_TIME, KEEP_ALIVE_UNIT, threadFactory);
//将线程池放到pool中
if (!pool.compareAndSet(NONE, update)) {
update.shutdown();
}
}
所以IoScheduler的构造方法主要是创建一个线程池，并保存，继续看createWorker()方法
public Worker createWorker() {
//创建EventLoopWorker，并将前面创建的线程池对象传过去
return new EventLoopWorker(pool.get());
}
看看EventLoopWorker构造方法做了什么
EventLoopWorker(CachedWorkerPool pool) {
//赋值
this.pool = pool;
this.tasks = new CompositeDisposable();
//获取threadWorker对象
this.threadWorker = pool.get();
}
ThreadWorker get() {
//判断是否解绑
if (allWorkers.isDisposed()) {
return SHUTDOWN_THREAD_WORKER;
}
//从expiringWorkerQueue队列中获取，获取到就返回
while (!expiringWorkerQueue.isEmpty()) {
ThreadWorker threadWorker = expiringWorkerQueue.poll();
if (threadWorker != null) {
return threadWorker;
}
}
// 没有获取到，创建一个返回
ThreadWorker w = new ThreadWorker(threadFactory);
//添加到allWorkers中
allWorkers.add(w);
return w;
}
往前看
public Disposable scheduleDirect(@NonNull Runnable run, long delay, @NonNull TimeUnit unit) {
//创建一个Worker，这里的Worker就是EventLoopWorker对象
final Worker w = createWorker();
//...
//调用schedule方法
w.schedule(task, delay, unit);
//返回task
return task;
}
继续看EventLoopWorker.schedule()方法
@NonNull
@Override
public Disposable schedule(@NonNull Runnable action, long delayTime, @NonNull TimeUnit unit) {
//判断是否解绑
if (tasks.isDisposed()) {
// don't schedule, we are unsubscribed
return EmptyDisposable.INSTANCE;
}
//调用scheduleActual方法
//其中threadWorker是构造方法时初始化的
return threadWorker.scheduleActual(action, delayTime, unit, tasks);
}
前面在EventLoopWorker的构造方法中已经介绍过threadWorker是如何初始化的了，看threadWorker.scheduleActual()方法做了什么
public ScheduledRunnable scheduleActual(final Runnable run, long delayTime, @NonNull TimeUnit unit, @Nullable DisposableContainer parent) {
//检查并判断，返回自身
Runnable decoratedRun = RxJavaPlugins.onSchedule(run);
//创建ScheduledRunnable对象，并将decoratedRun传过去
//ScheduledRunnable实现了Runnable
ScheduledRunnable sr = new ScheduledRunnable(decoratedRun, parent);
//调用parent.add方法，判断返回值
if (parent != null) {
if (!parent.add(sr)) {
return sr;
}
}
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) {
if (parent != null) {
parent.remove(sr);
}
RxJavaPlugins.onError(ex);
}
return sr;
}
parent 是前面传过来的，回溯一下很容易就知道是CompositeDisposable对象，看add()方法
public boolean add(@NonNull Disposable disposable) {
//判null
ObjectHelper.requireNonNull(disposable, "disposable is null");
//判断是否解绑，默认false
if (!disposed) {
synchronized (this) {
if (!disposed) {
//将disposable添加到OpenHashSet中去，返回true
OpenHashSet<Disposable> set = resources;
if (set == null) {
set = new OpenHashSet<Disposable>();
resources = set;
}
set.add(disposable);
return true;
}
}
}
disposable.dispose();
return false;
}
所以前面的parent.add(sr)返回true，所以继续往下走
public ScheduledRunnable scheduleActual(final Runnable run, long delayTime, @NonNull TimeUnit unit, @Nullable DisposableContainer parent) {
//....
Future<?> f;
try {
//判断是否延迟，根据上面可以知道delayTime为0
if (delayTime <= 0) {
//执行submit方法，executor是在构造方法中初始化的
f = executor.submit((Callable<Object>)sr);
} else {
f = executor.schedule((Callable<Object>)sr, delayTime, unit);
}
sr.setFuture(f);
} catch (RejectedExecutionException ex) {
if (parent != null) {
parent.remove(sr);
}
RxJavaPlugins.onError(ex);
}
return sr;
}
继续看executor怎么初始化的
public class NewThreadWorker extends Scheduler.Worker implements Disposable {
private final ScheduledExecutorService executor;
volatile boolean disposed;
public NewThreadWorker(ThreadFactory threadFactory) {
//初始化
executor = SchedulerPoolFactory.create(threadFactory);
}
//....
}
public static ScheduledExecutorService create(ThreadFactory factory) {
//返回一个线程池
final ScheduledExecutorService exec = Executors.newScheduledThreadPool(1, factory);
tryPutIntoPool(PURGE_ENABLED, exec);
return exec;
}
注意，前面说的threadWorker是NewThreadWorker的子类，所以executor就是一个线程池，executor.submit方法就会走传过去的Runnable的run方法，所以就会走到ScheduledRunnable.run 方法中
public void run() {
lazySet(THREAD_INDEX, Thread.currentThread());
try {
try {
//actual就是ScheduledRunnable构造方法中传过来的
actual.run();
} catch (Throwable e) {
// Exceptions.throwIfFatal(e); nowhere to go
RxJavaPlugins.onError(e);
}
} finally {
lazySet(THREAD_INDEX, null);
Object o = get(PARENT_INDEX);
if (o != PARENT_DISPOSED && compareAndSet(PARENT_INDEX, o, DONE) && o != null) {
((DisposableContainer)o).delete(this);
}
for (;;) {
o = get(FUTURE_INDEX);
if (o == SYNC_DISPOSED || o == ASYNC_DISPOSED || compareAndSet(FUTURE_INDEX, o, DONE)) {
break;
}
}
}
}
所以最后会回到我们传过来的Runnable的run 方法中，往前看，我们传过来的Runnable是什么
//ObservableSubscribeOn中
@Override
public void subscribeActual(final Observer<? super T> observer) {
final SubscribeOnObserver<T> parent = new SubscribeOnObserver<T>(observer);
observer.onSubscribe(parent);
//SubscribeTask就是我们说的传过去的Runnable对象
parent.setDisposable(scheduler.scheduleDirect(new SubscribeTask(parent)));
}
所以走了一大圈，回到了SubscribeTask的run方法中
final class SubscribeTask implements Runnable {
private final SubscribeOnObserver<T> parent;
SubscribeTask(SubscribeOnObserver<T> parent) {
this.parent = parent;
}
@Override
public void run() {
//调用source.subscribe方法，parent 就是SubscribeOnObserver
//source就是前面的Observable.create创建的对象
source.subscribe(parent);
}
}
又走到source.subscribe方法，其中source是Observable.create创建的对象，所以到了第一篇讲的内容里面了，所以回到下面这里
var sources = object : ObservableOnSubscribe<String> {
override fun subscribe(emitter: ObservableEmitter<String>) {
//走了一大圈，回到了这里，当前的emitter对象为SubscribeOnObserver
emitter.onNext("下一步")
emitter.onComplete()
}
}
var observable = Observable.create(sources)
走了一圈，回到了这里，不过需要注意的是，因为是在SubscribeTask的run方法中调用subscribe的方法，所以当前subscribe是运行在run方法中的，也就是说是运行在子线程中，所以我们的sources的subscribe方法就是在子线程中运行的，当调用emitter.onNext()时，就会到SubscribeOnObserver的onNext()方法，看SubscribeOnObserver做了什么
@Override
public void onNext(T t) {
downstream.onNext(t);
}
@Override
public void onError(Throwable t) {
downstream.onError(t);
}
@Override
public void onComplete() {
downstream.onComplete();
}
直接调用downstream.onNext，其中downstream就是observer对象，这样就到到observer的onNext中。
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