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[原创] Activity 原生启动流程分析
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发表于: 2025-5-3 20:48
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在 Android 系统启动以后，系统已经启动了 Zygote，ServiceManager，SystemServer 等系统进程。
ServiceManager 进程中完成了 Binder 初始化；SystemServer 进程中 ActivityManagerService，WindowManagerService，PackageManagerService 等系统服务在 ServiceManager 中已经注册；最后启动了 Launcher 桌面应用。
Launcher 作为用户的交互界面，在用户点击 APP 图标的时候提供了打开应用的能力。不同的手机厂商可能会根据 Launcher 做一些定制，比如 miui 就是如此，但最终的原理是一致的。
应用安装的时候，通过 PackageManagerService 解析 apk 的 AndroidManifest.xml 文件，提取出这个 apk 的信息写入到 packages.xml 文件中，这些信息包括：权限、应用包名、icon、apk 的安装位置、版本、userID 等等。packages.xml 文件位于系统目录下/data/system/packages.xml。
当用户点击桌面上的应用图标后，Launcher 会通过 service_manager 向 AMS 服务发出请求，查询对应的 APP 信息，然后由 Zygote 创建目标 APP 进程。
先梳理一下大致的流程：
具体到代码实现中，分为几个步骤，首先启动步骤从 Launcher 开始：
Launcher.startActivitySafel -> Launcher.startActivity
Activity.startActivity
Activity.startActivityForResult - Instrumentation.execStartActivity - ActivityTaskManager.getService().startActivity
ActivityManagerNative.getDefault() 会返回一个 ActivityManagerProxy 作为 Launcher 中使用 ActivityTaskManager 的代理，该代理的 startActivity 会发送 START_ACTIVITY_TRANSACTION 来通知 ActivityTaskManager
完成上述过程后，进程从 Launcher 切换到 system_server 中的 ActivityManagerService，也就是 AMS。
startActivity - startActivityAsUser
ActivityStackSupervisor.startActivityMayWait - resolveActivity
PackageManagerService.resolveIntent() - queryIntentActivities()
获取到调用者的进程信息，通过 Intent.FLAG_ACTIVITY_FORWARD_RESULT 判断是否需要进行 startActivityForResult 处理。检查调用者是否有权限来调用指定的 Activity
Activity 有多种启动模式，对 launchMode 的处理，创建 Task 等操作。启动 Activity 所在进程，已存在则直接 onResume()，不存在则创建 Activity 并处理是否触发 onNewIntent()。
ActivityStackSupervisor.startActivityUncheckedLocked - startActivityLocked
ActivityStack.resumeTopActivityInnerLocked
ActivityStackSupervisor.startSpecificActivity
我们考虑后者的情况，程序将会往下调用 startProcessAsync 创建新进程：
startProcessAsync 会通过消息的方式让 ATMS 服务在处理该消息时创建对应的进程，调用目标为 ActivityManagerInternal::startProcess
而 ActivityManagerInternal::startProcess 调用ActivityManagerService::startProcessLocked 调用 ProcessList::startProcessLocked 调用 ProcessList::startProcess
如果目标进程是 top app，设置 flag 保证启动的最高优先级，并最终在 startProcess 中创建对应的目标进程，也就是 APP 的进程。
在进程创建成功后，将当前进程切换到新进程，并将 ActivityThread 类加载到新进程，调用 ActivityThread.main
Looper 会持续从消息队列中获取消息，然后处理指定的任务。其中，attach 函数调用时会发送 ATTACH_APPLICATION_TRANSACTION 通知 system_server 中的服务。
此时，应用的 ActivityThread 和 ApplicationThread 已经被创建，并创建了消息循环机制。当调用 ActivityThread.attach 时，内部会调用 ActivityManagerProxy.attachApplication ，通过 Binder 来调用 AMS 中的 attachApplication 函数，此时会把 ApplicationThread 传递过去。
attachApplication - attachApplicationLocked 主要有两个关键函数需要关注：
我们先关注 thread.bindApplication ，thread 就是刚刚由新进程传过来的。
函数先调用 bindApplication 向进程发送 H.BIND_APPLICATION 命令，进程收到该命令后，通过 handleBindApplication 处理：
handleBindApplication 初始化 context，然后初始化 Instrumentation 对象，创建 Application 对象，并调用该对象的 onCreate
初始化流程调用链为 makeApplication - newApplication :
然后是 makeApplicationInner 的细节
对于新创建的这个进程而言，当 callApplicationOnCreate 完成调用以后，这个进程的上下文，以及 Application 对象和 Instrumentation 对象都完成的创建和初始化。而在进程这波完成上述的初始化过程中，AMS 那边也没闲着，在发送完相应的命令以后， ActivityManagerService#attachApplicationLocked 继续往下调用 ActivityTaskManagerService.LocalService#attachApplication
可以注意到，最终这个函数将往下执行 ActivityTaskSupervisor#realStartActivityLocked 完成最后的步骤。而如果此前不需要创建新进程，那么刚打开 APP 的时候就会从这个地方开始恢复进程的状态了。
函数首先创建 Activity 事务，设置对应的 callback ，以及对应的生命周期 ActivityLifecycleItem，最终开始调度事务 lientLifecycleManager#scheduleTransaction。
可以看到，最终由 AMS 向进程发出 H.EXECUTE_TRANSACTION 命令，这个命令同样会被进程那边接受并处理：
这个函数最终会往下调用 ClientTransactionHandler#handleLaunchActivity，最为抽象类的方法，实际调用 ActivityThread#handleLaunchActivity ：
handleLaunchActivity 最终回调目标 Activity 的 onConfigurationChanged，初始化 WindowManagerService，调用 ActivityThread.performLaunchActivity。
callActivityOnCreate 中会回调 Activity.performCreate ，其中调用 Activity 的 onCreate 、Activity.setContentView、ActivityThread.performResumeActivity，performResumeActivity 最终会回调 onResume。
总之，到这里之后，新应用的进程算是创建完成了。
弯弯绕绕一大圈，有不少的同名函数，在整理这些资料的时候也是被绕晕了好几次了，希望最终写出来的流程没有太混乱吧。如果有哪里写的不对，还请师傅们多多指教。
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void startProcessAsync(ActivityRecord activity, boolean knownToBeDead, boolean isTop,String hostingType) { try { ... // 发布消息以启动进程，以避免在持有 ATMS 锁的情况下调用 AMS 可能出现死锁。 final Message m = PooledLambda.obtainMessage(ActivityManagerInternal::startProcess, mAmInternal, activity.processName, activity.info.applicationInfo, knownToBeDead, isTop, hostingType, activity.intent.getComponent()); mH.sendMessage(m); } finally { Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER); }}void startProcessAsync(ActivityRecord activity, boolean knownToBeDead, boolean isTop,String hostingType) { try { ... // 发布消息以启动进程，以避免在持有 ATMS 锁的情况下调用 AMS 可能出现死锁。 final Message m = PooledLambda.obtainMessage(ActivityManagerInternal::startProcess, mAmInternal, activity.processName, activity.info.applicationInfo, knownToBeDead, isTop, hostingType, activity.intent.getComponent()); mH.sendMessage(m); } finally { Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER); }}public static void main(String[] args) { ... //初始化当前进程的 Looper 对象 Looper.prepareMainLooper(); ... ActivityThread thread = new ActivityThread(); //此处创建Application thread.attach(false, startSeq); if (sMainThreadHandler == null) { sMainThreadHandler = thread.getHandler(); } if (false) { Looper.myLooper().setMessageLogging(new LogPrinter(Log.DEBUG, "ActivityThread")); } // 调用 Looper 的 loop 方法开启无限循环。 Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited");}public static void main(String[] args) { ... //初始化当前进程的 Looper 对象 Looper.prepareMainLooper(); ... ActivityThread thread = new ActivityThread(); //此处创建Application thread.attach(false, startSeq); if (sMainThreadHandler == null) { sMainThreadHandler = thread.getHandler(); } if (false) { Looper.myLooper().setMessageLogging(new LogPrinter(Log.DEBUG, "ActivityThread")); } // 调用 Looper 的 loop 方法开启无限循环。 Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited");}private boolean attachApplicationLocked(@NonNull IApplicationThread thread, int pid, int callingUid, long startSeq) { synchronized (mProcLock) { app.mState.setCurAdj(ProcessList.INVALID_ADJ); app.mState.setSetAdj(ProcessList.INVALID_ADJ); app.mState.setVerifiedAdj(ProcessList.INVALID_ADJ); mOomAdjuster.setAttachingSchedGroupLSP(app); app.mState.setForcingToImportant(null); updateProcessForegroundLocked(app, false, 0, false); app.mState.setHasShownUi(false); app.mState.setCached(false); app.setDebugging(false); app.setKilledByAm(false); app.setKilled(false); app.setUnlocked(StorageManager.isUserKeyUnlocked(app.userId)); } // 移除进程超时信息 mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app); final ProviderInfoList providerList = ProviderInfoList.fromList(providers); if (app.getIsolatedEntryPoint() != null) { thread.runIsolatedEntryPoint( app.getIsolatedEntryPoint(), app.getIsolatedEntryPointArgs()); } else if (instr2 != null) { thread.bindApplication(processName, appInfo, app.sdkSandboxClientAppVolumeUuid, app.sdkSandboxClientAppPackage, providerList, instr2.mClass, profilerInfo, instr2.mArguments, instr2.mWatcher, instr2.mUiAutomationConnection, testMode, mBinderTransactionTrackingEnabled, enableTrackAllocation, isRestrictedBackupMode || !normalMode, app.isPersistent(), new Configuration(app.getWindowProcessController().getConfiguration()), app.getCompat(), getCommonServicesLocked(app.isolated), mCoreSettingsObserver.getCoreSettingsLocked(), buildSerial, autofillOptions, contentCaptureOptions, app.getDisabledCompatChanges(), serializedSystemFontMap, app.getStartElapsedTime(), app.getStartUptime()); } else { thread.bindApplication(processName, appInfo, app.sdkSandboxClientAppVolumeUuid, app.sdkSandboxClientAppPackage, providerList, null, profilerInfo, null, null, null, testMode, mBinderTransactionTrackingEnabled, enableTrackAllocation, isRestrictedBackupMode || !normalMode, app.isPersistent(), new Configuration(app.getWindowProcessController().getConfiguration()), app.getCompat(), getCommonServicesLocked(app.isolated), mCoreSettingsObserver.getCoreSettingsLocked(), buildSerial, autofillOptions, contentCaptureOptions, app.getDisabledCompatChanges(), serializedSystemFontMap, app.getStartElapsedTime(), app.getStartUptime()); } if (normalMode) { try { // 最终调用ActivityTaskManagerService.LocalService#attachApplication() didSomething = mAtmInternal.attachApplication(app.getWindowProcessController()); } catch (Exception e) { } } return true;}private boolean attachApplicationLocked(@NonNull IApplicationThread thread, int pid, int callingUid, long startSeq) { synchronized (mProcLock) { app.mState.setCurAdj(ProcessList.INVALID_ADJ); app.mState.setSetAdj(ProcessList.INVALID_ADJ); app.mState.setVerifiedAdj(ProcessList.INVALID_ADJ); mOomAdjuster.setAttachingSchedGroupLSP(app); app.mState.setForcingToImportant(null); updateProcessForegroundLocked(app, false, 0, false); app.mState.setHasShownUi(false); app.mState.setCached(false); app.setDebugging(false); app.setKilledByAm(false); app.setKilled(false); app.setUnlocked(StorageManager.isUserKeyUnlocked(app.userId)); } // 移除进程超时信息 mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app); final ProviderInfoList providerList = ProviderInfoList.fromList(providers); if (app.getIsolatedEntryPoint() != null) { thread.runIsolatedEntryPoint( app.getIsolatedEntryPoint(), app.getIsolatedEntryPointArgs()); } else if (instr2 != null) { thread.bindApplication(processName, appInfo, app.sdkSandboxClientAppVolumeUuid, app.sdkSandboxClientAppPackage, providerList, instr2.mClass, profilerInfo, instr2.mArguments, instr2.mWatcher, instr2.mUiAutomationConnection, testMode, mBinderTransactionTrackingEnabled, enableTrackAllocation, isRestrictedBackupMode || !normalMode, app.isPersistent(), new Configuration(app.getWindowProcessController().getConfiguration()), app.getCompat(), getCommonServicesLocked(app.isolated), mCoreSettingsObserver.getCoreSettingsLocked(), buildSerial, autofillOptions, contentCaptureOptions, app.getDisabledCompatChanges(), serializedSystemFontMap, app.getStartElapsedTime(), app.getStartUptime()); } else { thread.bindApplication(processName, appInfo, app.sdkSandboxClientAppVolumeUuid, app.sdkSandboxClientAppPackage, providerList, null, profilerInfo, null, null, null, testMode, mBinderTransactionTrackingEnabled, enableTrackAllocation, isRestrictedBackupMode || !normalMode, app.isPersistent(), new Configuration(app.getWindowProcessController().getConfiguration()), app.getCompat(), getCommonServicesLocked(app.isolated), mCoreSettingsObserver.getCoreSettingsLocked(), buildSerial, autofillOptions, contentCaptureOptions, app.getDisabledCompatChanges(), serializedSystemFontMap, app.getStartElapsedTime(), app.getStartUptime()); } if (normalMode) { try { // 最终调用ActivityTaskManagerService.LocalService#attachApplication() didSomething = mAtmInternal.attachApplication(app.getWindowProcessController()); } catch (Exception e) { } } return true;}private void handleBindApplication(AppBindData data) { // 初始化context final ContextImpl appContext = ContextImpl.createAppContext(this, data.info); // 初始化Instrumentation if (ii != null) { initInstrumentation(ii, data, appContext); } else { mInstrumentation = new Instrumentation(); mInstrumentation.basicInit(this); } Application app; try { // 初始化Application // 调用LoadedApk#makeApplicationInner() app = data.info.makeApplicationInner(data.restrictedBackupMode, null); mInstrumentation.onCreate(data.instrumentationArgs); // 回调Application#onCreate() mInstrumentation.callApplicationOnCreate(app); } finally { }}private void handleBindApplication(AppBindData data) { // 初始化context final ContextImpl appContext = ContextImpl.createAppContext(this, data.info); // 初始化Instrumentation if (ii != null) { initInstrumentation(ii, data, appContext); } else { mInstrumentation = new Instrumentation(); mInstrumentation.basicInit(this); } Application app; try { // 初始化Application // 调用LoadedApk#makeApplicationInner() app = data.info.makeApplicationInner(data.restrictedBackupMode, null); mInstrumentation.onCreate(data.instrumentationArgs); // 回调Application#onCreate() mInstrumentation.callApplicationOnCreate(app); } finally { }}private void handleBindApplication(AppBindData data) { // 初始化context final ContextImpl appContext = ContextImpl.createAppContext(this, data.info); // 初始化Instrumentation if (ii != null) { initInstrumentation(ii, data, appContext); } else { mInstrumentation = new Instrumentation(); mInstrumentation.basicInit(this); } Application app; try { // 初始化Application // 调用LoadedApk#makeApplicationInner() app = data.info.makeApplicationInner(data.restrictedBackupMode, null); mInstrumentation.onCreate(data.instrumentationArgs); // 回调Application#onCreate() mInstrumentation.callApplicationOnCreate(app); } finally { }}public Application makeApplication(boolean forceDefaultAppClass,Instrumentation instrumentation) { if (mApplication != null) { return mApplication; } String appClass = mApplicationInfo.className; java.lang.ClassLoader cl = getClassLoader(); //此时新建一个 Application 的 ContextImpl 对象， ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this); //通过在 handleBindApplication 创建的 mInstrumentation 对象新建一个 Application 对象，同时进行 attach。 app = mActivityThread.mInstrumentation.newApplication(cl, appClass, appContext); appContext.setOuterContext(app);}public Application newApplication(ClassLoader cl, String className, Context context) { return newApplication(cl.loadClass(className), context);}Instrumentation类：static public Application newApplication(Class<?> clazz, Context context) { //实例化 Application Application app = (Application)clazz.newInstance(); // Application 和 context绑定 app.attach(context); return app;}//attach 就是将新建的 ContextImpl 赋值到 mBase，这个 ContextImpl 对象就是所有Application 内 Context 的具体实现，同时赋值一些其他的信息如 mLoadedApk。final void attach(Context context) { mBase = base; mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;}private void handleBindApplication(AppBindData data) { // 初始化context final ContextImpl appContext = ContextImpl.createAppContext(this, data.info); // 初始化Instrumentation if (ii != null) { initInstrumentation(ii, data, appContext); } else { mInstrumentation = new Instrumentation(); mInstrumentation.basicInit(this); } Application app; try { // 初始化Application // 调用LoadedApk#makeApplicationInner() app = data.info.makeApplicationInner(data.restrictedBackupMode, null); mInstrumentation.onCreate(data.instrumentationArgs); // 回调Application#onCreate() mInstrumentation.callApplicationOnCreate(app); } finally { }}public Application makeApplication(boolean forceDefaultAppClass,Instrumentation instrumentation) { if (mApplication != null) { return mApplication; } String appClass = mApplicationInfo.className; java.lang.ClassLoader cl = getClassLoader(); //此时新建一个 Application 的 ContextImpl 对象， ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this); //通过在 handleBindApplication 创建的 mInstrumentation 对象新建一个 Application 对象，同时进行 attach。 app = mActivityThread.mInstrumentation.newApplication(cl, appClass, appContext); appContext.setOuterContext(app);}public Application newApplication(ClassLoader cl, String className, Context context) { return newApplication(cl.loadClass(className), context);}Instrumentation类：static public Application newApplication(Class<?> clazz, Context context) { //实例化 Application Application app = (Application)clazz.newInstance(); // Application 和 context绑定 app.attach(context); return app;}//attach 就是将新建的 ContextImpl 赋值到 mBase，这个 ContextImpl 对象就是所有Application 内 Context 的具体实现，同时赋值一些其他的信息如 mLoadedApk。final void attach(Context context) { mBase = base; mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;}public Application makeApplicationInner(boolean forceDefaultAppClass, Instrumentation instrumentation) { return makeApplicationInner(forceDefaultAppClass, instrumentation, false);}private Application makeApplicationInner(boolean forceDefaultAppClass, Instrumentation instrumentation, boolean allowDuplicateInstances) { if (mApplication != null) { return mApplication; } synchronized (sApplications) { final Application cached = sApplications.get(mPackageName); if (cached != null) { if (!allowDuplicateInstances) { mApplication = cached; return cached; } } } Application app = null; final String myProcessName = Process.myProcessName(); String appClass = mApplicationInfo.getCustomApplicationClassNameForProcess( myProcessName); try { final java.lang.ClassLoader cl = getClassLoader(); if (!mPackageName.equals("android")) { initializeJavaContextClassLoader(); } // 初始化Application的上下文 ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this); // 创建Application实例 app = mActivityThread.mInstrumentation.newApplication( cl, appClass, appContext); appContext.setOuterContext(app); } catch (Exception e) { } mActivityThread.mAllApplications.add(app); mApplication = app; if (!allowDuplicateInstances) { synchronized (sApplications) { sApplications.put(mPackageName, app); } } if (instrumentation != null) { try { // 回调Application#onCreate() instrumentation.callApplicationOnCreate(app); } catch (Exception e) { } } return app;}public Application makeApplicationInner(boolean forceDefaultAppClass, Instrumentation instrumentation) { return makeApplicationInner(forceDefaultAppClass, instrumentation, false);}private Application makeApplicationInner(boolean forceDefaultAppClass, Instrumentation instrumentation, boolean allowDuplicateInstances) { if (mApplication != null) { return mApplication; } synchronized (sApplications) { final Application cached = sApplications.get(mPackageName);[培训]Windows内核深度攻防：从Hook技术到Rootkit实战！
