LeakCanary:检测所有的内存泄漏

左手的ㄟ右手 2022-09-21 13:12 202阅读 0赞

原文： [LeakCanary: Detect all memory leaks!][LeakCanary_ Detect all memory leaks]

http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2015/0509/2854.html

### 没人喜欢OutOfMemoryError    ###

在Square的注册过程中，我们在bitmap上 [绘制了一个用户的签名][Link 1]。这个bitmap和设备的屏幕大小相当，在创建它的时候，我遇到了相当数量的OOM导致的崩溃。

![signature.png][]

我们试过了几种方法，没有一个解决了我们的问题：

*  使用`Bitmap.Config.ALPHA_8`（签名是不需要颜色的）
 *  捕获`OutOfMemoryError`，触发垃圾回收然后重试几次（从[GCUtils][] 获得的启发）
 *  我们没有考虑过将bitmap分配在堆内存之外，那个时候[Fresco][] 还没出现。

### 我们看待问题的方式是不对的 ###

bitmap的大小本身不是什么问题。当内存快要满了的时候，OOM随时随地都可能发生。尤其是在创建大对象的时候更容易发生，比如bitmap。OOM一般代表着更深层次的问题：内存泄漏。

### 什么是内存泄漏? ###

有些对象只有有限的生命周期。当它们的任务完成之后，它们将被垃圾回收。如果在对象的生命周期本该结束的时候，这个对象还被一系列的引用，这就会导致内存泄漏。随着泄漏的累积，app将消耗完内存。

比如，在`Activity.onDestroy()`被调用之后，view树以及相关的bitmap都应该被垃圾回收。如果一个正在运行的后台线程继续持有这个Activity的引用，那么相关的内存将不会被回收，这最终将导致`OutOfMemoryError崩溃。`

### 寻找内存泄漏 ###

寻找内存泄漏是一个人工操作的过程，在Raizlabs的 [Wrangling Dalvik][] 系列中描述得很清楚。

下面是关键的步骤：

1.  通过 [Bugsnag][], [Crashlytics][], 或者 [Developer Console][]了解OOM
2.  主动重现问题。你可能需要买或者借或者偷一个遭遇了崩溃的特殊设备（并不是所有的设备上都会发生内存泄漏！）。你还需要找出是什么串在一起导致了内存泄漏。  
    
3.  当OOM出现时进行堆转储(dump the heap)([这里介绍了如何做][Link 2]).
4.  使用MAT或YourKit内存检测工具检测内存的变化，并找出哪个对象应该被垃圾回收;
5.  从那个对象到GC roots推断最短的强引用路径;
6.  在路径中找出不存在的引用，并修复memory leak;

要是有一个库可以为你做完所有的事情，让你专注于修复内存泄漏的问题，那该有多好。

### LeakCanary介绍 ###

[LeakCanary][] 是一个开源的在debug版本中检测内存泄漏的java库。

让我们来看看一个cait的例子：

<table style="border-collapse:collapse; border-spacing:0px; border:1px rgb(51,51,51); width:847px; font-family:verdana,arial,sans-serif; font-size:11px; margin:0px!important; padding:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; min-height:auto!important; background:none!important"> 
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     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
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      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">}</code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">class&nbsp;Box&nbsp;{ </code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">&nbsp;&nbsp;</code> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">Cat&nbsp;hiddenCat;</code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">}</code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">class&nbsp;Docker&nbsp;{ </code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">&nbsp;&nbsp;</code> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">static&nbsp;Box&nbsp;container;</code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">}</code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important">
       &nbsp; 
     </div> 
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      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important; color:rgb(0,130,0)!important">//&nbsp;...</code> 
     </div> 
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       &nbsp; 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">Box&nbsp;box&nbsp;=&nbsp;</code> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important; color:rgb(0,102,153)!important">new</code>&nbsp; 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">Box();</code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">Cat&nbsp;schrodingerCat&nbsp;=&nbsp;</code> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important; color:rgb(0,102,153)!important">new</code>&nbsp; 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">Cat();</code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">box.hiddenCat&nbsp;=&nbsp;schrodingerCat;</code> 
     </div> 
     <div style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important"> 
      <code style="font-family:Consolas,&quot;Liberation Mono&quot;,Menlo,Courier,monospace; margin:0px; padding:0.2em 0px; line-height:normal; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:auto!important">Docker.container&nbsp;=&nbsp;box;</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

创建一个`RefWatcher`实例，然后给它一个对象让它观察：

当检测出泄漏的时候，你会自动得到一个漂亮的泄漏线索：

我们知道你的时间宝贵，因此我们让它非常好设置。只需几行代码，LeakCanary就能自动检测Activity的泄漏：

当内存不足时，会有一个通知和良好的展示界面：

![leaktrace.png][]

### 结论 ###

在启用LeakCanary之后，我们发现和修复了许多内存泄漏的问题。我们甚至发现了一些[ Android SDK中的泄漏][Android SDK]。

结果是非常令人惊奇的，我们现在减少了94%的oom崩溃问题。

![oom\_rate.png][oom_rate.png]

如果你想终结OOM崩溃，[现在就安装LeakCanary][LeakCanary]!

[LeakCanary_ Detect all memory leaks]: https://corner.squareup.com/2015/05/leak-canary.html
[Link 1]: https://corner.squareup.com/2010/07/smooth-signatures.html
[signature.png]: http://www.jcodecraeer.com/uploads/20150509/1431183030136174.png
[GCUtils]: https://android.googlesource.com/platform/packages/inputmethods/LatinIME/+/ics-mr1/java/src/com/android/inputmethod/latin/Utils.java
[Fresco]: https://github.com/facebook/fresco
[Wrangling Dalvik]: http://www.raizlabs.com/dev/2014/03/wrangling-dalvik-memory-management-in-android-part-1-of-2/
[Bugsnag]: https://bugsnag.com/
[Crashlytics]: https://try.crashlytics.com/
[Developer Console]: https://play.google.com/apps/publish/
[Link 2]: https://gist.github.com/pyricau/4726389fd64f3b7c6f32
[LeakCanary]: https://github.com/square/leakcanary
[leaktrace.png]: /images/20220721/bdb4b23e43874366ae511c997bb2ea13.png
[Android SDK]: https://github.com/square/leakcanary/blob/master/library/leakcanary-android/src/main/java/com/squareup/leakcanary/AndroidExcludedRefs.java
[oom_rate.png]: http://www.jcodecraeer.com/uploads/20150509/1431182925125282.png