乾貨 | Trip.com APP 啓動優化實踐

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App的啓動優化實踐，從分析App啓動的過程開始，在瞭解啓動流程的基礎上制定大的優化原則和小的具體方案，希望能對大家有所幫助。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"一、App啓動的流程分析"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"想做啓動優化，首先要了解清楚啓動的各個流程，然後才能對各個環節去做針對性措施。"}]},{"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對啓動階段的定義圖："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.geekbang.org\/infoq\/ce\/cea0e917c4380ae7dc613e8cb63f7b63.png","alt":"圖片","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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文件，幸運是大部分是系統庫，且系統會在操作系統啓動時計算和緩存系統動態庫。"}]},{"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":"Apple爲了解決安全問題，引入"},{"type":"codeinline","content":[{"type":"text","text":"ASLR"}]},{"type":"text","text":"和"},{"type":"codeinline","content":[{"type":"text","text":"Code Sign"}]},{"type":"text","text":"，如果不作符號修正，程序將沒法正常運行，所以會有Rebase和Bind過程。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.geekbang.org\/infoq\/f0\/f0572ce87eb87cb3dda7b1ca67af8e80.png","alt":"圖片","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":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Rebase"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在鏡像內部調整指針的指向，其實就是將內部指針都加上偏移量（Slide=實際新地址-舊地址）"}]},{"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":"Bind"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"修正指外部的指針，比如上圖中malloc，這個符號不存在於我們App的Mach-O中，需要從外部的鏡像中獲取，這時候就需要Bind操作把這個關聯起來。"}]},{"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":"libSystem 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Init"}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Objc和Swift的初始化"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通過"},{"type":"codeinline","content":[{"type":"text","text":"_dyld_objc_notify_register"}]},{"type":"text","text":"註冊回調，在image加載完時初始化語言相關。"}]},{"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":"加載category"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在上面語言初始化完之後，會加載所有category，處理category的所有方法，協議和屬性等。"}]},{"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":"調用所有+load"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"也是通過向 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的幾個生命週期調用："}]},{"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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具體方案"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.1 減少動態庫"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"動態庫的加載在啓動階段是必須的，所以我們要儘量減少非必要的動態庫。對此我們做了以下幾點："}]},{"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）梳理所有動態庫，將用不到的或者可以簡單替代的動態庫刪除"}]},{"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":"可以通過"},{"type":"codeinline","content":[{"type":"text","text":"otool -L 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合併category"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"合併category，可以減少category加載時的耗時。不過這部分收益不大，並且也會影響編程習慣，所以我們並沒有投入很多時間，不再贅述。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.4 刪除+load"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"以前會有很多代碼爲了省事，加到了+load中，這部分很顯然佔用啓動時間，所以儘量要把這其中的代碼轉移，可以放到initialize中懶加載，或者放到啓動任務中併發執行，儘量減少這部分的影響。"}]},{"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":"Xcode調試時，可以通過正則添加所有+load方法的斷點"},{"type":"codeinline","content":[{"type":"text","text":"br s -r \"\\+\\[.+ load\\]$\""}]},{"type":"text","text":" ，然後使用"},{"type":"codeinline","content":[{"type":"text","text":"br 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啓動任務併發"}]},{"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":"裏面執行的所有啓動任務不作任何處理，那麼代碼框架將會很亂，你的優化也只能單點單點去做。"}]},{"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":"所以我們將"},{"type":"codeinline","content":[{"type":"text","text":"application:didFinishLaunchingWithOptions:"}]},{"type":"text","text":"階段所有方法任務化，一個任務做一種類型的事。任務拆分好之後，就可以根據任務之間的相關性，選擇哪些任務是可以併發執行，哪些任務是必須有依賴關係前後執行。"}]},{"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":"圖片","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":"現在："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.geekbang.org\/infoq\/ef\/efefd0878a9060f7d46f99b6ac098584.png","alt":"圖片","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":"當然，任務的拆分顆粒度也很重要，拆分太粗的話，很難達到最優的組合，可能一個任務裏的方法之間仍然有並行的空間。拆分太細的話，也有可能導致同一時間併發數太多，造成額外的線程切換開銷。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.7 I\/O處理"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"尤其要注意啓動階段的I\/O，一般出現於讀取磁盤中的文件，比如配置文件等。"}]},{"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":"使用 Instrument→App Launch 去查看啓動過程就會發現，如果主線程執行出現很多灰色的塊，那就是I\/O，找到這些I\/O產生的方法，儘量在子線程併發執行，避免阻塞主線程。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.8 首頁數據的預加載和懶加載"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首頁上有很多數據要加載，比如圖片、上次緩存在本地的數據等等，這些數據的加載如果在寫代碼時不作特殊處理，那會在主線程執行，不知不覺就會有很多耗時。"}]},{"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）預加載"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對首頁渲染必須的數據，比如一個icon，或者一個翻譯的數據，我們通過在啓動任務（之前提到的拆分的併發任務）中新增加一個預加載啓動任務，專門負責在"},{"type":"codeinline","content":[{"type":"text","text":"application:didFinishLaunchingWithOptions:"}]},{"type":"text","text":" 的過程中併發執行數據的獲取。因爲獲取數據大多比較耗時，所以放在子線程充分利用啓動階段的空閒。同時這類任務大多數是I\/O操作，並不會佔用太多CPU資源。"}]},{"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":"更進一步，其實可以對首頁用到的資源在運行時作個標記，記錄到磁盤，下次啓動的時候讀取這個記錄，對用到的資源進行提前預加載，這樣避免hard code很多資源名在代碼中。"}]},{"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）懶加載"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首頁的數據往往很多，但並不是一開始要全部用到。可以對數據作區分，和第一屏展示無關的，使用懶加載，真正用到的時候再去加載。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.9 二進制重排"}]},{"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":"由於虛擬內存的機制，應用啓動時不會把所有數據加載到內存，而是以頁爲單位逐步從磁盤中加載，內存中的虛擬地址和磁盤中的物理地址有個映射關係。當程序執行時，如果發現要訪問的東西不在內存裏，就會觸發一次"},{"type":"codeinline","content":[{"type":"text","text":"page fault"}]},{"type":"text","text":" ，去磁盤中加載新的一頁。"}]},{"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":"啓動階段有很多方法要調用，而這些方法在Mach-O中的位置又是在編譯時確認的。如果有10個方法剛好在不同頁，可能就要產生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":"二進制重排要做的就是將啓動階段要用到的方法，在編譯時提前確定，通過.order文件告訴編譯器，這樣這些方法會排布在Mach-O的最前面，之前的10次"},{"type":"codeinline","content":[{"type":"text","text":"page fault"}]},{"type":"text","text":" 很可能就變成一兩次"},{"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":"通過在Other C Flags中添加"},{"type":"codeinline","content":[{"type":"text","text":"-fsanitize-coverage=func,trace-pc-guard"}]},{"type":"text","text":" 再通過"},{"type":"codeinline","content":[{"type":"text","text":"__sanitizer_cov_trace_pc_guard"}]},{"type":"text","text":"記錄啓動階段所有方法的調用，再將這些寫入到.order文件中，在Xcode的"},{"type":"codeinline","content":[{"type":"text","text":"ORDER_FILE"}]},{"type":"text","text":" 設置中配置即可生效。"}]},{"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":"通過測試，我們的二進制重排大概優化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":"針對啓動任務和首頁渲染階段，通用的手段是通過instrument，profile出耗時長的任務，對任務針對性地做方法優化。如果有的方法是第三方庫的，那就需要推進社區去更新。我們在做的過程中給Firebase和Google的一些SDK提了很多issue，對方開發人員配合很積極，對我們幫助很大。"}]},{"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":"通過長期的優化，以上手段全部用完之後，我們的啓動時間從原來的2秒，優化到1秒以內。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"總結"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在優化啓動時間的過程中，我們的收穫不僅是對啓動時間的優化，也對系統的啓動機制有了更深的瞭解，同時優化了我們自己的代碼，使其變得更加更加健壯和高性能。"}]},{"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":"作者簡介"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Shanks，攜程移動開發專家，關注移動端基礎技術。"}]},{"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":"本文轉載自：攜程技術中心（ID：ctriptech）"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"原文鏈接："},{"type":"link","attrs":{"href":"https:\/\/mp.weixin.qq.com\/s\/smWjs2X8HWvcvKW_DSXYJA","title":"xxx","type":null},"content":[{"type":"text","text":"乾貨 | Trip.com APP 啓動優化實踐"}]}]}]}