干货 | Trip.com APP 启动优化实践

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App的启动优化实践，从分析App启动的过程开始，在了解启动流程的基础上制定大的优化原则和小的具体方案，希望能对大家有所帮助。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"一、App启动的流程分析"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"想做启动优化，首先要了解清楚启动的各个流程，然后才能对各个环节去做针对性措施。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"借用WWDC对启动阶段的定义图："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.geekbang.org\/infoq\/ce\/cea0e917c4380ae7dc613e8cb63f7b63.png","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"1.1 System 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的几个生命周期调用："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"application:willFinishLaunchingWithOptions:"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"application:didFinishLaunchingWithOptions:"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"applicationDidBecomeActive:"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"scene:willConnectToSession:options:"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"sceneWillEnterForeground:"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"sceneDidBecomeActive:"}]}]}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"1.5 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总体原则"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"不管哪个流程，我们都想尽量遵循下面两个原则："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"删"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"删的原则是指，对App启动和运行不是必须的任务，或者跟首页渲染第一帧无关的任务，都从启动流程中删除。对于删除的任务，可以进行懒加载的形式，需要时再调用；也可以换到其他的时机去触发，比如首页渲染完之后。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"压"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"压的原则是指，对App启动和运行必须的任务，或者直接影响首页渲染第一帧的任务，都尽可能压缩其运行时间。至于做法，可以是优化方法内的实现，使其运行更快；也可以将方法执行的线程切换到子线程，以并发的形式降低其对整个启动过程的影响。"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.2 具体方案"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.1 减少动态库"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"动态库的加载在启动阶段是必须的，所以我们要尽量减少非必要的动态库。对此我们做了以下几点："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1）梳理所有动态库，将用不到的或者可以简单替代的动态库删除"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可以通过"},{"type":"codeinline","content":[{"type":"text","text":"otool -L 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启动任务并发"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"想象一下，如果"},{"type":"codeinline","content":[{"type":"text","text":"application:didFinishLaunchingWithOptions:"}]},{"type":"text","text":"里面执行的所有启动任务不作任何处理，那么代码框架将会很乱，你的优化也只能单点单点去做。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以我们将"},{"type":"codeinline","content":[{"type":"text","text":"application:didFinishLaunchingWithOptions:"}]},{"type":"text","text":"阶段所有方法任务化，一个任务做一种类型的事。任务拆分好之后，就可以根据任务之间的相关性，选择哪些任务是可以并发执行，哪些任务是必须有依赖关系前后执行。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"以前："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.geekbang.org\/infoq\/5c\/5cd64985aa766e62ec4baf9a031bc038.png","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"现在："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.geekbang.org\/infoq\/ef\/efefd0878a9060f7d46f99b6ac098584.png","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当然，任务的拆分颗粒度也很重要，拆分太粗的话，很难达到最优的组合，可能一个任务里的方法之间仍然有并行的空间。拆分太细的话，也有可能导致同一时间并发数太多，造成额外的线程切换开销。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.7 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首页数据的预加载和懒加载"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首页上有很多数据要加载，比如图片、上次缓存在本地的数据等等，这些数据的加载如果在写代码时不作特殊处理，那会在主线程执行，不知不觉就会有很多耗时。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1）预加载"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"对首页渲染必须的数据，比如一个icon，或者一个翻译的数据，我们通过在启动任务（之前提到的拆分的并发任务）中新增加一个预加载启动任务，专门负责在"},{"type":"codeinline","content":[{"type":"text","text":"application:didFinishLaunchingWithOptions:"}]},{"type":"text","text":" 的过程中并发执行数据的获取。因为获取数据大多比较耗时，所以放在子线程充分利用启动阶段的空闲。同时这类任务大多数是I\/O操作，并不会占用太多CPU资源。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"更进一步，其实可以对首页用到的资源在运行时作个标记，记录到磁盘，下次启动的时候读取这个记录，对用到的资源进行提前预加载，这样避免hard code很多资源名在代码中。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2）懒加载"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首页的数据往往很多，但并不是一开始要全部用到。可以对数据作区分，和第一屏展示无关的，使用懒加载，真正用到的时候再去加载。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.9 二进制重排"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1）"},{"type":"codeinline","content":[{"type":"text","text":"page fault"}]},{"type":"text","text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"由于虚拟内存的机制，应用启动时不会把所有数据加载到内存，而是以页为单位逐步从磁盘中加载，内存中的虚拟地址和磁盘中的物理地址有个映射关系。当程序执行时，如果发现要访问的东西不在内存里，就会触发一次"},{"type":"codeinline","content":[{"type":"text","text":"page fault"}]},{"type":"text","text":" ，去磁盘中加载新的一页。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"启动阶段有很多方法要调用，而这些方法在Mach-O中的位置又是在编译时确认的。如果有10个方法刚好在不同页，可能就要产生10次"},{"type":"codeinline","content":[{"type":"text","text":"page fault"}]},{"type":"text","text":" 。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"二进制重排要做的就是将启动阶段要用到的方法，在编译时提前确定，通过.order文件告诉编译器，这样这些方法会排布在Mach-O的最前面，之前的10次"},{"type":"codeinline","content":[{"type":"text","text":"page fault"}]},{"type":"text","text":" 很可能就变成一两次"},{"type":"codeinline","content":[{"type":"text","text":"page fault"}]},{"type":"text","text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过在Other C Flags中添加"},{"type":"codeinline","content":[{"type":"text","text":"-fsanitize-coverage=func,trace-pc-guard"}]},{"type":"text","text":" 再通过"},{"type":"codeinline","content":[{"type":"text","text":"__sanitizer_cov_trace_pc_guard"}]},{"type":"text","text":"记录启动阶段所有方法的调用，再将这些写入到.order文件中，在Xcode的"},{"type":"codeinline","content":[{"type":"text","text":"ORDER_FILE"}]},{"type":"text","text":" 设置中配置即可生效。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过测试，我们的二进制重排大概优化100-200ms。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.10 其他通用手段"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"针对启动任务和首页渲染阶段，通用的手段是通过instrument，profile出耗时长的任务，对任务针对性地做方法优化。如果有的方法是第三方库的，那就需要推进社区去更新。我们在做的过程中给Firebase和Google的一些SDK提了很多issue，对方开发人员配合很积极，对我们帮助很大。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"三、成果如何"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过长期的优化，以上手段全部用完之后，我们的启动时间从原来的2秒，优化到1秒以内。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"总结"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在优化启动时间的过程中，我们的收获不仅是对启动时间的优化，也对系统的启动机制有了更深的了解，同时优化了我们自己的代码，使其变得更加更加健壮和高性能。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"作者简介"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Shanks，携程移动开发专家，关注移动端基础技术。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文转载自：携程技术中心（ID：ctriptech）"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"原文链接："},{"type":"link","attrs":{"href":"https:\/\/mp.weixin.qq.com\/s\/smWjs2X8HWvcvKW_DSXYJA","title":"xxx","type":null},"content":[{"type":"text","text":"干货 | Trip.com APP 启动优化实践"}]}]}]}