activityThread之內容分析

 

 

2.讀Android源碼-冷啟動時的ActivityThread

1.Android ActivityThread工作原理

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2.讀Android源碼-冷啟動時的ActivityThread

 

前言：
應用冷啟動時需要創建進程，開啟主線程，實例化應用所需組件。
讀ActivityThread源碼有助於我們了解這個過程中，客戶端做的那些事。

冷啟動創建應用時，ActivityThread的主要方法：

1. main()
   -- 1. 開啟消息循環
   -- 2. 通知ActivityManagerService
   -- 3. 添加GCWatcher
2. handleBindApplication()
   -- 1. 創建LoadedApk
   -- 2. 創建Instrumentation
   -- 3. 創建Application
   -- 4. 通過Instrumentation調用Application的onCreate()方法

main()

main方法是一個應用創建的入口，他主要做了3件事

1. 開啟消息循環

調用Looper.prepareLoop() Looper.loop()，開啟主線程的消息循環，以便於ApplicationThread調用ActivityThread中的生命周期方法。

public static void main(String[] args) { ... Looper.prepareMainLooper(); ActivityThread thread = new ActivityThread(); thread.attach(false); if (sMainThreadHandler == null) { sMainThreadHandler = thread.getHandler(); } ... Looper.loop(); } 

2. 通知ActivityManagerService

調用ActivityThread.attach()方法，attach()方法在調用了attachApplication()將ApplicationThread這個Binder交給了ActivityManagerService，意味着ActivityManagerService可以通過ApplicationThread控制我們的應用，建立了服務器端對客戶端的通信渠道。

private void attach(boolean system){ ... final IActivityManager mgr = ActivityManager.getService(); try { mgr.attachApplication(mAppThread); } catch (RemoteException ex) { throw ex.rethrowFromSystemServer(); } ... } 

^{SDK26以后，去除了Native和Proxy，而是直接從ActivityManager(ServiceManager)中獲取ActivityManagerService的Binder對象進行通信}

3. 添加GCWatcher

在attach()方法中，添加了監聽dialvik內存使用情況得監聽者GcWatcher，當內存使用超過總容量的3/4，則打印Log進行記錄，並且調用ActivityManagerService的releaseSomeActivities()進行內存釋放操作，以防止內存溢出導致應用崩潰。

private void attach(boolean system){ ... BinderInternal.addGcWatcher(new Runnable() { @Override public void run() { if (!mSomeActivitiesChanged) { return; } Runtime runtime = Runtime.getRuntime(); long dalvikMax = runtime.maxMemory(); long dalvikUsed = runtime.totalMemory() - runtime.freeMemory(); if (dalvikUsed > ((3*dalvikMax)/4)) { if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024) + " total=" + (runtime.totalMemory()/1024) + " used=" + (dalvikUsed/1024)); mSomeActivitiesChanged = false; try { mgr.releaseSomeActivities(mAppThread); } catch (RemoteException e) { throw e.rethrowFromSystemServer(); } } } }); ... } 

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handleBindApplication()

^{ActivityManagerService=AMS}
handleBindApplication的被調用時機是:

1. 通過上面AMS.attachApplication()后，AMS獲得了控制應用的Binder對象ApplicationThread。
2. AMS進行了一系列操作后（這里先省略），調用了ApplicationThread的bindApplication()
3. bindApplication中通過消息機制，sendMessage到ActivityThread，調用了ActivityThread的handleBindApplication()

handleBindApplication是創建用於所需組件的入口，他主要做了4件事：

1. 創建LoadedApk

LoadedApk對象包含應用的所有信息

private void handleBindApplication(AppBindData data){ ... final LoadedApk pi = getPackageInfo(instrApp, data.compatInfo, appContext.getClassLoader(), false, true, false); ... } 

2. 創建Instrumentation

Instrumentation是應用組件的管家，組件的生命周期方法都需要通過它來調用，是客戶端與服務器端通信的最后一步。

private void handleBindApplication(AppBindData data){ ... final ContextImpl instrContext = ContextImpl.createAppContext(this, pi); try { final ClassLoader cl = instrContext.getClassLoader(); mInstrumentation = (Instrumentation) cl.loadClass(data.instrumentationName.getClassName()).newInstance(); } catch (Exception e) { throw new RuntimeException( "Unable to instantiate instrumentation " + data.instrumentationName + ": " + e.toString(), e); } ... } 

3. 創建Application

調用了LoadedApk.makeApplication()進行Application的創建

private void handleBindApplication(AppBindData data){ ... app = data.info.makeApplication(data.restrictedBackupMode, null); ... } 

• 先通過ContextImpl.createAppContext(）獲得Application的Context
• 再通過Instrumentation.newApplication()，用ClassLoder創建Applicaition
• 創建后Applicaition調用自身的attach(Context)方法，將Context與Applicaition綁定，完成創建

LoadedApk.class public Application makeApplication(boolean forceDefaultAppClass, Instrumentation instrumentation) { ... Application app = null; ... ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this); app = mActivityThread.mInstrumentation.newApplication( cl, appClass, appContext); ... return app; } 

4. 通過Instrumentation調用Application的onCreate()方法

private void handleBindApplication(AppBindData data){ ... mInstrumentation.callApplicationOnCreate(app); ... } 

更新中...

 1.Android ActivityThread工作原理

 

導讀

• 移動開發知識體系總章（Java基礎、Android、Flutter）
• Android Handler消息機制 、 Android中為什么主線程不會因為Looper.loop里的無限循環ANR?

通過前面的學習（復習）我們知道ActivityThread其實不是一個Thread，而是一個final類型的Java類，並且擁有main(String[] args) 方法。Android原生以Java語言為基礎，Java的JVM啟動的入口就是main(String[] args)。

    public static void main(String[] args) { Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain"); // Install selective syscall interception AndroidOs.install(); // CloseGuard defaults to true and can be quite spammy. We // disable it here, but selectively enable it later (via // StrictMode) on debug builds, but using DropBox, not logs. CloseGuard.setEnabled(false); Environment.initForCurrentUser(); // Make sure TrustedCertificateStore looks in the right place for CA certificates final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId()); TrustedCertificateStore.setDefaultUserDirectory(configDir); Process.setArgV0("<pre-initialized>"); Looper.prepareMainLooper(); // Find the value for {@link #PROC_START_SEQ_IDENT} if provided on the command line. // It will be in the format "seq=114" long startSeq = 0; if (args != null) { for (int i = args.length - 1; i >= 0; --i) { if (args[i] != null && args[i].startsWith(PROC_START_SEQ_IDENT)) { startSeq = Long.parseLong( args[i].substring(PROC_START_SEQ_IDENT.length())); } } } ActivityThread thread = new ActivityThread(); thread.attach(false, startSeq); if (sMainThreadHandler == null) { sMainThreadHandler = thread.getHandler(); } if (false) { Looper.myLooper().setMessageLogging(new LogPrinter(Log.DEBUG, "ActivityThread")); } // End of event ActivityThreadMain. Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); } 

以上為main方法中的全部代碼，我們關注以下幾點：

• Looper.prepareMainLooper();
• Looper.loop();
• thread.attach(false, startSeq);
• thread.getHandler();

Looper.prepareMainLooper();

主程序Looper的初始化工作

    public static void prepareMainLooper() { prepare(false); synchronized (Looper.class) { if (sMainLooper != null) { throw new IllegalStateException("The main Looper has already been prepared."); } sMainLooper = myLooper(); } } private static void prepare(boolean quitAllowed) { if (sThreadLocal.get() != null) { throw new RuntimeException("Only one Looper may be created per thread"); } sThreadLocal.set(new Looper(quitAllowed)); } public static @Nullable Looper myLooper() { return sThreadLocal.get(); } 

可以看到new Looper的時候傳了false

Looper.loop();

1.Looper就是字面意思（輪訓器），在loop方法中無限循環的去MessageQueue（消息隊列）中讀取消息。

2. MessageQueue則通過next方法無限循環的進行消息出隊，無消息時則會進入睡眠

執行thread.attach(false, startSeq);

通過thread.attach(false, startSeq);把ActivityThread 和主線程進行綁定。

執行thread.getHandler();