rxjava是一个在java虚拟机上的响应式扩展，通过使用可观察的序列将异步和基于事件的程序组合起来的一个库。
它扩展了观察者模式来支持数据/事件序列，并且添加了操作符，这些操作符允许你声明性地组合序列，同时抽象出要关注的问题：比如低级线程、同步、线程安全和并发数据结构等。
rxjava相信大家都非常了解吧，今天分享一下rxjava的 消息发送 和线程源码的分析。最后并分享一个相关demo,让大家更加熟悉我们天天都在用的框架。
消息订阅发送
首先让我们看看消息订阅发送最基本的代码组成：
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observable observable = observable.create( new observableonsubscribe<string>() { @override public void subscribe(observableemitter<string> emitter) throws exception { emitter.onnext( "jack1" ); emitter.onnext( "jack2" ); emitter.onnext( "jack3" ); emitter.oncomplete(); } });
observer<string> observer = new observer<string>() { @override public void onsubscribe(disposable d) { log.d(tag, "onsubscribe" ); }
@override public void onnext(string s) { log.d(tag, "onnext : " + s); }
@override public void onerror(throwable e) { log.d(tag, "onerror : " + e.tostring()); }
@override public void oncomplete() { log.d(tag, "oncomplete" ); } };
observable.subscribe(observer); |
代码很简单,observable为被观察者,observer为观察者,然后通过observable.subscribe(observer),把观察者和被观察者关联起来。被观察者发送消息(emitter.onnext("内容")),观察者就可以在onnext()方法里回调出来。
我们先来看observable，创建是用observable.create()方法进行创建，源码如下：
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public static <t> observable<t> create(observableonsubscribe<t> source) { objecthelper.requirenonnull(source, "source is null" ); return rxjavaplugins.onassembly( new observablecreate<t>(source)); }
public static <t> t requirenonnull(t object, string message) { if (object == null ) { throw new nullpointerexception(message); } return object; }
public static <t> observable<t> onassembly( @nonnull observable<t> source) { function<? super observable, ? extends observable> f = onobservableassembly; if (f != null ) { return apply(f, source); } return source; } |
可以看出，create()方法里最主要的还是创建用observableonsubscribe传入创建了一个observablecreate对象并且保存而已。
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public final class observablecreate<t> extends observable<t> { final observableonsubscribe<t> source;
public observablecreate(observableonsubscribe<t> source) { this .source = source; }
} |
接着是创建observer，这比较简单只是单纯创建一个接口对象而已
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public interface observer<t> { void onsubscribe( @nonnull disposable d);
void onnext( @nonnull t t);
void onerror( @nonnull throwable e);
void oncomplete(); } |
订阅发送消息
observable.subscribe(observer)的subscribe方法如下：
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public final void subscribe(observer<? super t> observer) { objecthelper.requirenonnull(observer, "observer is null" ); try { observer = rxjavaplugins.onsubscribe( this , observer); objecthelper.requirenonnull(observer, "plugin returned null observer" ); subscribeactual(observer); } catch (nullpointerexception e) { // nopmd throw e; } catch (throwable e) { exceptions.throwiffatal(e); rxjavaplugins.onerror(e); nullpointerexception npe = new nullpointerexception( "actually not, but can't throw other exceptions due to rs" ); npe.initcause(e); throw npe; } }
//objecthelper.requirenonnull()方法 public static <t> t requirenonnull(t object, string message) { if (object == null ) { throw new nullpointerexception(message); } return object; }
//rxjavaplugins.onsubscribe()方法 public static <t> observer<? super t> onsubscribe( @nonnull observable<t> source, @nonnull observer<? super t> observer) { bifunction<? super observable, ? super observer, ? extends observer> f = onobservablesubscribe; if (f != null ) { return apply(f, source, observer); } return observer; } |
从上面源码可以看出requirenonnull()只是做非空判断而已，而rxjavaplugins.onsubscribe()也只是返回最终的观察者而已。所以关键代码是抽象方法subscribeactual(observer);那么subscribeactual对应哪个代码段呢？
还记得observable.create()创建的observablecreate类吗，这就是subscribeactual()具体实现类，源码如下：
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protected void subscribeactual(observer<? super t> observer) { createemitter<t> parent = new createemitter<t>(observer); observer.onsubscribe(parent); try { source.subscribe(parent); } catch (throwable ex) { exceptions.throwiffatal(ex); parent.onerror(ex); } } |
从上面的代码可以看出，首先创建了一个createemitter对象并传入observer，然后回到observer的onsubscribe()方法，而source就是我们之前创建observablecreate传入的observableonsubscribe对象。
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class createemitter<t> extends atomicreference<disposable> implements observableemitter<t>, disposable {
} |
而createemitter又继承observableemitter接口，又回调observableonsubscribe的subscribe方法，对应着我们的：
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observable observable = observable.create( new observableonsubscribe<string>() { @override public void subscribe(observableemitter<string> emitter) throws exception { emitter.onnext( "jack1" ); emitter.onnext( "jack2" ); emitter.onnext( "jack3" ); emitter.oncomplete(); } }); |
当它发送消息既调用emitter.onnext()方法时，既调用了createemitter的onnext()方法：
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public void onnext(t t) { if (t == null ) { onerror( new nullpointerexception( "onnext called with null. null values are generally not allowed in 2.x operators and sources." )); return ; } if (!isdisposed()) { observer.onnext(t); } } |
可以看到最终又回调了观察者的onnext()方法，把被观察者的数据传输给了观察者。有人会问
isdisposed()是什么意思，是判断要不要终止传递的，我们看emitter.oncomplete()源码：
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public void oncomplete() { if (!isdisposed()) { try { observer.oncomplete(); } finally { dispose(); } } }
public static boolean dispose(atomicreference<disposable> field) { disposable current = field.get(); disposable d = disposed; if (current != d) { current = field.getandset(d); if (current != d) { if (current != null ) { current.dispose(); } return true ; } } return false ; }
public static boolean isdisposed(disposable d) { return d == disposed; } |
dispose()方法是终止消息传递，也就付了个disposed常量，而isdisposed()方法就是判断这个常量而已。这就是整个消息订阅发送的过程，用的是观察者模式。
线程切换
在上面模板代码的基础上，线程切换只是改变了如下代码：
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observable.subscribeon(schedulers.io()) .observeon(androidschedulers.mainthread()) .subscribe(observer); |
下面我们对线程切换的源码进行一下分析，分为两部分：subscribeon()和observeon()
subscribeon()
首先是subscribeon()源码如下：
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public final observable<t> subscribeon(scheduler scheduler) { objecthelper.requirenonnull(scheduler, "scheduler is null" ); return rxjavaplugins.onassembly( new observablesubscribeon<t>( this , scheduler)); } |
我们传进去了一个scheduler类，scheduler是一个调度类，能够延时或周期性地去执行一个任务。
scheduler有如下类型：
| ioscheduler | schedulers.io() | io操作线程 | 读写sd卡文件，查询数据库，访问网络等io密集型操作 |
| newthreadscheduler | schedulers.newthread() | 创建新线程 | 耗时操作等 |
| singlescheduler | schedulers.single() | 单例线程 | 只需一个单例线程时 |
| computationscheduler | schedulers测试数据putation() | cpu计算操作线程 | 图片压缩取样、xml,json解析等cpu密集型计算 |
| trampolinescheduler | schedulers.trampoline() | 当前线程 | 需要在当前线程立即执行任务时 |
| handlerscheduler | androidschedulers.mainthread() | android主线程 | 更新ui等 |
接着就没什么了，只是返回一个observablesubscribeon对象而已。
observeon()
首先看源码如下：
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public final observable<t> observeon(scheduler scheduler) { return observeon(scheduler, false , buffersize()); }
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)); } |
这里也是没什么，只是最终返回一个observableobserveon对象而已。
接着还是像原来那样调用subscribe()方法进行订阅，看起来好像整体变化不大，就是封装了一些对象而已，不过着恰恰是rxjava源码的精华，当他再次调用subscribeactual()方法时，已经不是之前的observablecreate()里subscribeactual方法了，而是最先调用observableobserveon的subscribeactual()方法，对应源码如下：
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protected void subscribeactual(observer<? super t> observer) { if (scheduler instanceof trampolinescheduler) { source.subscribe(observer); } else { scheduler.worker w = scheduler.createworker(); source.subscribe( new observeonobserver<t>(observer, w, delayerror, buffersize)); } } |
在这里有两点要讲，一点是observeonobserver是执行观察者的线程，后面还会详解，然后就是source.subscribe，这个source.subscribe调的是observablesubscribeon的subscribe方法，而subscribe方法因为继承的也是observable，是observable里的方法，所以和上面的observablecreate一样的方法，所以会调用observablesubscribeon里的subscribeactual()方法，对应的代码如下：
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public void subscribeactual( final observer<? super t> s) { final subscribeonobserver<t> parent = new subscribeonobserver<t>(s); s.onsubscribe(parent); parent.setdisposable(scheduler.scheduledirect( new subscribetask(parent))); } |
上面代码中，首先把observeonobserver返回给来的用subscribeonobserver[包装]起来，然后在回调observer的onsubscribe()，就是对应模板代码的onsubscribe()方法。
接着看subscribetask类的源码：
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final class subscribetask implements runnable { private final subscribeonobserver<t> parent; subscribetask(subscribeonobserver<t> parent) { this .parent = parent; } @override public void run() { source.subscribe(parent); } } |
其中的source.subscribe(parent)，就是我们执行子线程的回调方法，对应我们模板代码里的被观察者的subscribe()方法。它放在run()方法里，并且继承runnable,说明这个类主要是线程运行。接着看scheduler.scheduledirect()方法对应的源码如下：
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public disposable scheduledirect( @nonnull runnable run) { return scheduledirect(run, 0l, timeunit.nanoseconds); }
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); return task; } |
在这里，createworker()也是一个抽象方法，调用的是我们的调度类对应的schedulers类里面的方法，这里是ioscheduler类，
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public final class ioscheduler extends scheduler{
final atomicreference<cachedworkerpool> pool;
//省略....
public worker createworker() { return new eventloopworker(pool.get()); }
static final class eventloopworker extends scheduler.worker { private final compositedisposable tasks; private final cachedworkerpool pool; private final threadworker threadworker;
final atomicboolean once = new atomicboolean();
eventloopworker(cachedworkerpool pool) { this .pool = pool; this .tasks = new compositedisposable(); this .threadworker = pool.get(); }
//省略....
@nonnull @override public disposable schedule( @nonnull runnable action, long delaytime, @nonnull timeunit unit) { if (tasks.isdisposed()) { // don't schedule, we are unsubscribed return emptydisposable.instance; } return threadworker.scheduleactual(action, delaytime, unit, tasks); } }
}
static final class cachedworkerpool implements runnable {
//省略....
threadworker get() { if (allworkers.isdisposed()) { return shutdown_thread_worker; } while (!expiringworkerqueue.isempty()) { threadworker threadworker = expiringworkerqueue.poll(); if (threadworker != null ) { return threadworker; } }
threadworker w = new threadworker(threadfactory); allworkers.add(w); return w; } //省略.... } |
这就是ioscheduler的createworker()的方法，其实最主要的意思就是获取线程池，以便于生成子线程，让subscribetask()可以运行。然后直接调用 w.schedule(task, delay, unit)方法让它在线程池里执行。上面中那threadworker的源码如下：
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static final class threadworker extends newthreadworker { private long expirationtime; threadworker(threadfactory threadfactory) { super (threadfactory); this .expirationtime = 0l; }
//省略代码.... }
public class newthreadworker extends scheduler.worker implements disposable { private final scheduledexecutorservice executor;
public newthreadworker(threadfactory threadfactory) { executor = schedulerpoolfactory.create(threadfactory); }
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);
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; } } |
可以看到，这就调了原始的javaapi来进行线程池操作。
然后最后一环在子线程调用source.subscribe(parent)方法，然后回调刚开始创建的observablecreate的subscribeactual(),既：
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protected void subscribeactual(observer<? super t> observer) { createemitter<t> parent = new createemitter<t>(observer); observer.onsubscribe(parent); try { source.subscribe(parent); } catch (throwable ex) { exceptions.throwiffatal(ex); parent.onerror(ex); } } |
进行消息的订阅绑定。
当我们在调用 emitter.onnext(内容)时，是在io线程里的，那回调的onnext()又是什么时候切换的？那就是前面为了整个流程流畅性没讲的在observeon()里的observeonobserver是执行观察者的线程的过程。
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class observeonobserver<t> extends basicintqueuedisposable<t> implements observer<t>, runnable {
//省略代码....
observeonobserver(observer<? super t> actual, scheduler.worker worker, boolean delayerror, int buffersize) { this .actual = actual; this .worker = worker; this .delayerror = delayerror; this .buffersize = buffersize; }
@override public void onsubscribe(disposable s) { if (disposablehelper.validate( this .s, s)) { this .s = s; if (s instanceof queuedisposable) { @suppresswarnings ( "unchecked" ) queuedisposable<t> qd = (queuedisposable<t>) s; int m = qd.requestfusion(queuedisposable.any | queuedisposable.boundary); if (m == queuedisposable.sync) { sourcemode = m; queue = qd; done = true ; actual.onsubscribe( this ); schedule(); return ; } if (m == queuedisposable.async) { sourcemode = m; queue = qd; actual.onsubscribe( this ); return ; } } queue = new spsclinkedarrayqueue<t>(buffersize); actual.onsubscribe( this ); } }
@override public void onnext(t t) { if (done) { return ; } if (sourcemode != queuedisposable.async) { queue.offer(t); } schedule(); }
void schedule() { if (getandincrement() == 0 ) { worker.schedule( this ); } } //省略代码.... } |
当调用emitter.onnext(内容)方法，会调用上面的onnext()方法，然后在这个方法里会把数据压入一个队列，然后执行worker.schedule(this)方法，work是什么呢，还记得androidschedulers.mainthread()吗，这个对应这个handlerscheduler这个类，所以createworker()对应着：
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private static final class mainholder { static final scheduler default = new handlerscheduler( new handler(looper.getmainlooper())); }
public worker createworker() { return new handlerworker(handler); }
private static final class handlerworker extends worker { private final handler handler; private volatile boolean disposed;
handlerworker(handler handler) { this .handler = handler; }
@override public disposable schedule(runnable run, long delay, timeunit unit) { if (run == null ) throw new nullpointerexception( "run == null" ); if (unit == null ) throw new nullpointerexception( "unit == null" ); if (disposed) { return disposables.disposed(); } run = rxjavaplugins.onschedule(run); scheduledrunnable scheduled = new scheduledrunnable(handler, run); message message = message.obtain(handler, scheduled); message.obj = this ; // used as token for batch disposal of this worker's runnables. handler.sendmessagedelayed(message, unit.tomillis(delay)); if (disposed) { handler.removecallbacks(scheduled); return disposables.disposed(); } return scheduled; } } |
在next()方法里，运用android自带的handler消息机制，通过把方法包裹在message里，同通过handler.sendmessagedelayed()发送消息，就会在ui线程里回调next()方法，从而实现从子线程切换到android主线程的操作。我们在主线程拿到数据就可以进行各种在主线程的操作了。
总结一下：
observablecreate 一> observablesubscribeon 一> observableobserveon为初始化顺序
当调用observable.subscribe(observer)时的执行顺序
observableobserveon 一> observablesubscribeon 一> observablecreate
当发送消息的执行顺序
observablecreate 一> observablesubscribeon 一> observableobserveon
以上就是消息订阅和线程切换的源码的所有讲解了。
为了让你们理解更清楚，我仿照rxjava写了大概的消息订阅和线程切换的最基本代码和基本功能，以帮助你们理解
https://github测试数据/jack921/rxjava2demo
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。
原文链接：https://HdhCmsTestjianshu测试数据/p/264b68fd96fa
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