Rx中的线程切换

╰+攻爆jí腚メ 2022-08-18 15:18 156阅读 0赞

初学者在使用`RxJava`的过程中，经常搞不清Observable的事件序列和每次操作应该怎样切换线程，切换哪个线程  
首先需要搞懂在`RxJava` 中`.subscribeOn()` 和 `observeOn()` 之间的区别：  
\- `.subscribeOn()` 用来指定`Observable`应该操作的调度器(`Scheduler`)  
\- `.observeOn()` 指定 `Observable`在一个指定的调度器(`Scheduler`)上给观察者发送通知  
\- 默认情况下， 事件序列操作的线程与调用`.subscribe()`的线程一致

没理解？

> 英文原文: [https://medium.com/@diolor/observe-in-the-correct-thread-1939bb9bb9d2\#.nn1m7lrb8][https_medium.com_diolor_observe-in-the-correct-thread-1939bb9bb9d2_.nn1m7lrb8]  
> 翻译: [hanks][]  
> 注: 不是完全翻译,添加了具体例子

## 例子 ##

### 1.主线程 / .subscribe() 线程 ###

在 Activity的 `onCreate()`(主线程) 方法中添加以下代码：

Observable.just(1,2,3)
      .subscribe();

调用情况如下：

![图片][37e26756-da0d-46bb-bb2f-9b77ff067957.png]

**实验:**

Observable.just(1,2,3)
                .doOnNext(new Action1<Integer>() {
                    @Override public void call(Integer integer) {
                        Log.i("RxThread", "doOnNext:" + integer +", run In :" + Thread.currentThread().getName() );
                    }
                })
                .subscribe(new Action1<Integer>() {
                    @Override public void call(Integer integer) {
                        Log.i("RxThread", "get result:" + integer +", run In :" + Thread.currentThread().getName() );
                    }
                });

**输出结果:**

12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: doOnNext:1, run In :main
    12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: get result:1, run In :main
    12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: doOnNext:2, run In :main
    12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: get result:2, run In :main
    12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: doOnNext:3, run In :main
    12-06 16:14:39.225 15603-15603/com.hanks.rxsearch I/RxThread: get result:3, run In :main

### 2. .subscribeOn() ###

即使你在主线程中添加下面的代码，但是整段代码将运行在 `.subscribeOn()`定义的线程上

Observable.just(1,2,3)
      .subscribeOn(Schedulers.newThread())
      .subscribe();

![图片][5004ed8c-6b4d-42fc-93d8-ed22c4af79d3.png]

**实验:**

Observable.just(1,2,3)
               .doOnNext(new Action1<Integer>() {
                   @Override public void call(Integer integer) {
                       Log.i("RxThread", "doOnNext:" + integer +", run In :" + Thread.currentThread().getName() );
                   }
               })
               .subscribeOn(Schedulers.newThread())
               .subscribe(new Action1<Integer>() {
                   @Override public void call(Integer integer) {
                       Log.i("RxThread", "get result:" + integer +", run In :" + Thread.currentThread().getName() );
                   }
               });

**输出结果:**

12-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: doOnNext:1, run In :RxNewThreadScheduler-1
    12-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: get result:1, run In :RxNewThreadScheduler-1
    12-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: doOnNext:2, run In :RxNewThreadScheduler-1
    12-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: get result:2, run In :RxNewThreadScheduler-1
    12-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: doOnNext:3, run In :RxNewThreadScheduler-1
    12-06 16:13:17.717 14294-14319/com.hanks.rxsearch I/RxThread: get result:3, run In :RxNewThreadScheduler-1

### 3. .observeOn() ###

加入在主线程中添加下面的代码，首先 `Observable` 将在 `.subscribe()` 的线程上创建，但是 `.observeOn()`方法被调用之后，代码将运行在指定的线程上：

Observable.just(1,2,3)
      .observeOn(Schedulers.newThread())
      .subscribe();

![图片][97cc479d-fd85-4825-bdfa-b3b3b742a829.png]

**实验:**

new Thread() {
               @Override public void run() {
                   Observable.just(1, 2, 3).doOnNext(new Action1<Integer>() {
                       @Override public void call(Integer integer) {
                           Log.i("RxThread", "doOnNext:" + integer + ", run In :" + Thread.currentThread()
                                   .getName());
                       }
                   })
                   .observeOn(AndroidSchedulers.mainThread())
                   .subscribe(new Action1<Integer>() {
                       @Override public void call(Integer integer) {
                           Log.i("RxThread", "get result:" + integer + ", run In :" + Thread.currentThread()
                                   .getName());
                       }
                   });
    
               }
           }.start();

**输出结果:**

12-06 16:18:06.493 18584-18606/com.hanks.rxsearch I/RxThread: doOnNext:1, run In :Thread-155
    12-06 16:18:06.493 18584-18606/com.hanks.rxsearch I/RxThread: doOnNext:2, run In :Thread-155
    12-06 16:18:06.493 18584-18606/com.hanks.rxsearch I/RxThread: doOnNext:3, run In :Thread-155
    12-06 16:18:06.521 18584-18584/com.hanks.rxsearch I/RxThread: get result:1, run In :main
    12-06 16:18:06.521 18584-18584/com.hanks.rxsearch I/RxThread: get result:2, run In :main
    12-06 16:18:06.521 18584-18584/com.hanks.rxsearch I/RxThread: get result:3, run In :main

### 3. Combined logic ###

由于操作可以被组合使用,于是有了下面的代码：

Observable.just(1,2,3)
      .subscribeOn(Schedulers.newThread())
      .observeOn(Schedulers.newThread())
      .subscribe();

![图片][5abaaea0-babd-490c-abcb-6d404d3aa285.png]

**实验:**

new Thread() {
         @Override public void run() {
             Observable.just(1, 2, 3).doOnNext(new Action1<Integer>() {
                 @Override public void call(Integer integer) {
                     Log.i("RxThread", "doOnNext:" + integer + ", run In :" + Thread.currentThread()
                             .getName());
                 }
             })
             .subscribeOn(Schedulers.newThread())
             .observeOn(AndroidSchedulers.mainThread())
             .subscribe(new Action1<Integer>() {
                 @Override public void call(Integer integer) {
                     Log.i("RxThread", "get result:" + integer + ", run In :" + Thread.currentThread()
                             .getName());
                 }
             });
         }
     }.start();

**输出结果:**

12-06 16:19:53.066 20247-20274/com.hanks.rxsearch I/RxThread: doOnNext:1, run In :RxNewThreadScheduler-1
    12-06 16:19:53.066 20247-20274/com.hanks.rxsearch I/RxThread: doOnNext:2, run In :RxNewThreadScheduler-1
    12-06 16:19:53.066 20247-20274/com.hanks.rxsearch I/RxThread: doOnNext:3, run In :RxNewThreadScheduler-1
    12-06 16:19:53.077 20247-20247/com.hanks.rxsearch I/RxThread: get result:1, run In :main
    12-06 16:19:53.077 20247-20247/com.hanks.rxsearch I/RxThread: get result:2, run In :main
    12-06 16:19:53.077 20247-20247/com.hanks.rxsearch I/RxThread: get result:3, run In :main

## Tips / Gotchas: ##

### 1. “UI线程运行异常” ###

Observable.just(1,2,3)
      .subscribeOn(Schedulers.newThread())
      .subscribe(/** logic which touches ui **//); //在newThread中调用

obviously.

### 2. 逻辑处理放在后台(newThread) ###

错误姿势：

Observable.just(1,2,3)
      .subscribeOn(Schedulers.newThread())
      .observeOn(AndroidSchedulers.mainThread())
      .flatMap(/** logic which doesn't touch ui **//)
      .subscribe();

**实验:**

new Thread() {
           @Override public void run() {
               Observable.just("Android-Picasso", "Android-Glide", "Android-Fresco").doOnNext(new Action1<String>() {
                   @Override public void call(String str) {
                       Log.i("RxThread", "doOnNext:" + str + ", run In :" + Thread.currentThread()
                               .getName());
                   }
               })
               .subscribeOn(Schedulers.newThread())
               .observeOn(AndroidSchedulers.mainThread())
               .flatMap(new Func1<String, Observable<String>>() {
                   @Override public Observable<String> call(String str) {
                       Log.i("RxThread", "flatMap:" + str + ", run In :" + Thread.currentThread());
                       return Observable.from(str.split("-") ); // 返回平方
                   }
               })
               .subscribe(new Action1<String>() {
                   @Override public void call(String str) {
                       Log.i("RxThread", "get result:" + str + ", run In :" + Thread.currentThread()
                               .getName());
                   }
               });
           }
       }.start();

**输出结果:**

12-06 16:43:00.181 8161-8190/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxNewThreadScheduler-1
    12-06 16:43:00.181 8161-8190/com.hanks.rxsearch I/RxThread: doOnNext:Android-Glide, run In :RxNewThreadScheduler-1
    12-06 16:43:00.181 8161-8190/com.hanks.rxsearch I/RxThread: doOnNext:Android-Fresco, run In :RxNewThreadScheduler-1
    12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: flatMap:Android-Picasso, run In :Thread[main,5,main]
    12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Android, run In :main
    12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Picasso, run In :main
    12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: flatMap:Android-Glide, run In :Thread[main,5,main]
    12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Android, run In :main
    12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Glide, run In :main
    12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: flatMap:Android-Fresco, run In :Thread[main,5,main]
    12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Android, run In :main
    12-06 16:43:00.243 8161-8161/com.hanks.rxsearch I/RxThread: get result:Fresco, run In :main

正确姿势:

Observable.just(1,2,3)
      .subscribeOn(Schedulers.newThread())
      .flatMap(/** logic which doesn't touch ui **//)
      .observeOn(AndroidSchedulers.mainThread())
      .subscribe();

第二段代码中 `flatMap` (或者其他逻辑处理)将运行在后台线程， 如果是在Android中，这样做不会阻塞UI，阻塞UI的话有可能导致ANR之类的异常。这跟 `AsyncTask`中的 `doInBackground()`类似，在 `doInBackground()`中做耗时操作

**实验:**

new Thread() {
           @Override public void run() {
               Observable.just("Android-Picasso", "Android-Glide", "Android-Fresco").doOnNext(new Action1<String>() {
                   @Override public void call(String str) {
                       Log.i("RxThread", "doOnNext:" + str + ", run In :" + Thread.currentThread()
                               .getName());
                   }
               })
               .subscribeOn(Schedulers.newThread())
               .flatMap(new Func1<String, Observable<String>>() {
                   @Override public Observable<String> call(String str) {
                       Log.i("RxThread", "flatMap:" + str + ", run In :" + Thread.currentThread());
                       return Observable.from(str.split("-") ); // 返回平方
                   }
               })
               .observeOn(AndroidSchedulers.mainThread())
               .subscribe(new Action1<String>() {
                   @Override public void call(String str) {
                       Log.i("RxThread", "get result:" + str + ", run In :" + Thread.currentThread()
                               .getName());
                   }
               });
           }
       }.start();

**输出结果:**

12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxNewThreadScheduler-1
    12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: flatMap:Android-Picasso, run In :Thread[RxNewThreadScheduler-1,5,main]
    12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: doOnNext:Android-Glide, run In :RxNewThreadScheduler-1
    12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: flatMap:Android-Glide, run In :Thread[RxNewThreadScheduler-1,5,main]
    12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: doOnNext:Android-Fresco, run In :RxNewThreadScheduler-1
    12-06 16:41:27.025 6812-6839/com.hanks.rxsearch I/RxThread: flatMap:Android-Fresco, run In :Thread[RxNewThreadScheduler-1,5,main]
    12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Android, run In :main
    12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Picasso, run In :main
    12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Android, run In :main
    12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Glide, run In :main
    12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Android, run In :main
    12-06 16:41:27.043 6812-6812/com.hanks.rxsearch I/RxThread: get result:Fresco, run In :main

### 3. 最早的 `.subscribeOn()` 生效 ###

看下面的代码：

Observable.just(1,2,3)
      .subscribeOn(thread1)
      .subscribeOn(thread2)
      .subscribe();

`Observable` 的创建和 `.subscribeOn()` 的调用都将在 thread1 上面执行，所以没有必要多次调用 `.subscribeOn()`,因为只有第一次的是有用的。

**实验:**

new Thread() {
          @Override public void run() {
              Observable.just("Android-Picasso", "Android-Glide", "Android-Fresco").doOnNext(new Action1<String>() {
                  @Override public void call(String str) {
                      Log.i("RxThread", "doOnNext:" + str + ", run In :" + Thread.currentThread()
                              .getName());
                  }
              })
              .subscribeOn(Schedulers.newThread())
              .subscribeOn(Schedulers.io())
              .subscribeOn(Schedulers.computation())
              .subscribe(new Action1<String>() {
                  @Override public void call(String str) {
                      Log.i("RxThread", "get result:" + str + ", run In :" + Thread.currentThread()
                              .getName());
                  }
              });
          }
      }.start();

**输出结果**

12-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxNewThreadScheduler-1
    12-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: get result:Android-Picasso, run In :RxNewThreadScheduler-1
    12-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: doOnNext:Android-Glide, run In :RxNewThreadScheduler-1
    12-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: get result:Android-Glide, run In :RxNewThreadScheduler-1
    12-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: doOnNext:Android-Fresco, run In :RxNewThreadScheduler-1
    12-06 16:51:17.581 15622-15652/com.hanks.rxsearch I/RxThread: get result:Android-Fresco, run In :RxNewThreadScheduler-1

**实验**

new Thread() {
           @Override public void run() {
               Observable.just("Android-Picasso", "Android-Glide", "Android-Fresco").doOnNext(new Action1<String>() {
                   @Override public void call(String str) {
                       Log.i("RxThread", "doOnNext:" + str + ", run In :" + Thread.currentThread()
                               .getName());
                   }
               })
               .subscribeOn(Schedulers.io())
               .subscribeOn(Schedulers.newThread())
               .subscribeOn(Schedulers.computation())
               .subscribe(new Action1<String>() {
                   @Override public void call(String str) {
                       Log.i("RxThread", "get result:" + str + ", run In :" + Thread.currentThread()
                               .getName());
                   }
               });
           }
       }.start();

**输出结果**

12-06 16:52:13.378 16424-16454/com.hanks.rxsearch I/RxThread: doOnNext:Android-Picasso, run In :RxCachedThreadScheduler-2
    12-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: get result:Android-Picasso, run In :RxCachedThreadScheduler-2
    12-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: doOnNext:Android-Glide, run In :RxCachedThreadScheduler-2
    12-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: get result:Android-Glide, run In :RxCachedThreadScheduler-2
    12-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: doOnNext:Android-Fresco, run In :RxCachedThreadScheduler-2
    12-06 16:52:13.379 16424-16454/com.hanks.rxsearch I/RxThread: get result:Android-Fresco, run In :RxCachedThreadScheduler-2

`Android` `Rxjava` `Rxandroid`

> **文章出处** ([http://hanks.xyz][http_hanks.xyz])

[https_medium.com_diolor_observe-in-the-correct-thread-1939bb9bb9d2_.nn1m7lrb8]: https://medium.com/@diolor/observe-in-the-correct-thread-1939bb9bb9d2#.nn1m7lrb8
[hanks]: https://github.com/hanks-zyh
[37e26756-da0d-46bb-bb2f-9b77ff067957.png]: https://dn-coding-net-production-pp.qbox.me/37e26756-da0d-46bb-bb2f-9b77ff067957.png
[5004ed8c-6b4d-42fc-93d8-ed22c4af79d3.png]: https://dn-coding-net-production-pp.qbox.me/5004ed8c-6b4d-42fc-93d8-ed22c4af79d3.png
[97cc479d-fd85-4825-bdfa-b3b3b742a829.png]: https://dn-coding-net-production-pp.qbox.me/97cc479d-fd85-4825-bdfa-b3b3b742a829.png
[5abaaea0-babd-490c-abcb-6d404d3aa285.png]: https://dn-coding-net-production-pp.qbox.me/5abaaea0-babd-490c-abcb-6d404d3aa285.png
[http_hanks.xyz]: http://hanks.xyz