摘要:上一节我们讲完了Android10.0的ActivityManagerService的启动流程,在AMS的最后启动了Launcher进程,今天我们就来看看Launcher的真正启动流程。
阅读本文大约需要花费50分钟。
文章的内容主要还是从源码进行分析,虽然又臭又长,但是如果想要学习Android系统源码,这是必要走的路,没有捷径。
相对于碎片学习,我更倾向于静下心来花费1个小时认真的学习一段内容。
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[Android取经之路] 的源码都基于Android-Q(10.0) 进行分析
[Android取经之路] 系列文章:
《系统启动篇》
《日志系统篇》
《Binder通信原理》:
上一节我们学习了AMS\ATM的启动流程,这一节主要来学习Launcher的启动流程。
在Android的中,桌面应用Launcher由Launcher演变到Launcher2,再到现在的Launcher3,Google也做了很多改动。
Launcher不支持桌面小工具动画效果,Launcher2添加了动画效果和3D初步效果支持,从Android 4.4 (KK)开始Launcher默认使用Launcher3, Launcher3加入了透明状态栏,增加overview模式,可以调整workspace上页面的前后顺序,可以动态管理屏幕数量,widget列表与app list分开显示等功能。
我们主要研究Launcher3的启动过程。
/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
/frameworks/base/core/java/com/android/internal/os/ZygoteServer.java
/frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java
/frameworks/base/core/java/com/android/internal/os/Zygote.java
/frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
/frameworks/base/services/java/com/android/server/SystemServer.java
/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
/frameworks/base/services/core/java/com/android/server/am/ProcessList.java
/frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
/frameworks/base/services/core/java/com/android/server/wm/ActivityStartController.java
/frameworks/base/services/core/java/com/android/server/wm/ActivityStarter.java
/frameworks/base/services/core/java/com/android/server/wm/ActivityStack.java
/frameworks/base/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
/frameworks/base/services/core/java/com/android/server/wm/RootActivityContainer.java
/frameworks/base/services/core/java/com/android/server/wm/ClientLifecycleManager.java
/frameworks/base/core/java/android/os/Process.java
/frameworks/base/core/java/android/os/ZygoteProcess.java
/frameworks/base/core/java/android/app/ActivityThread.java
/frameworks/base/core/java/android/app/Activity.java
/frameworks/base/core/java/android/app/ActivityManagerInternal.java
/frameworks/base/core/java/android/app/servertransaction/ClientTransaction.java
/frameworks/base/core/java/android/app/servertransaction/ClientTransaction.aidl
/frameworks/base/core/java/android/app/ClientTransactionHandler.java
/frameworks/base/core/java/android/app/servertransaction/TransactionExecutor.java
/frameworks/base/core/java/android/app/servertransaction/LaunchActivityItem.java
/frameworks/base/core/java/android/app/Instrumentation.java
/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
从上面的代码路径可以看出,Android10.0中 Activity的相关功能被放到了wm的目录中,在Android9.0中是在am目录中,Google 最终的目的是把activity 和window融合,在Android10中只是做了简单的代码路径的变更,正在的功能还要到后面的版本才能慢慢融合。
主要代码作用:
负责调用Activity和Application生命周期。
负责Activity管理和调度等工作。
ATM是Android10中新增内容
负责管理四大组件和进程,包括生命周期和状态切换。
是由ActivityTaskManagerService对外提供的一个抽象类,真正的实现是在 ActivityTaskManagerService#LocalService
管理应用程序进程中主线程的执行
负责所有Activity栈的管理
主要作用是执行ClientTransaction
生命周期的管理调用
Android启动流程图:
Launcher启动序列图:
内容较多,例如Zygote的fork流程,realStartActivityLocked启动Activity的中间过程,都没有列出,下一个章节会单独来讲这部分内容
上一节在AMS启动过程中,我们知道了AMS启动完成前,在systemReady()中会去调用startHomeOnAllDisplays()来启动Launcher,本次就从startHomeOnAllDisplays()函数入口,来看看Launcher是如何被启动起来的。
[ActivityManagerService.java]
public void systemReady(final Runnable goingCallback, TimingsTraceLog
traceLog) {
...
//启动Home Activity
mAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");
...
}
Launcher的启动由三部分启动:
SystemServer完成启动Launcher Activity的调用
Zygote()进行Launcher进程的Fork操作
进入ActivityThread的main(),完成最终Launcher的onCreate操作
接下来我们分别从源码部分来分析这三个启动过程。
4.1第一阶段SystemServer 启动HomeActivity的调用阶段
调用栈:
[ActivityTaskManagerService.java] startHomeOnAllDisplays()
说明:ActivityTaskManagerInternal是 ActivityTaskManagerService的一个抽象类,正在的实现是在ActivityTaskManagerService的LocalService,所以mAtmInternal.startHomeOnAllDisplays()最终调用的是ActivityTaskManagerService的startHomeOnAllDisplays()方法
源码:
public boolean startHomeOnAllDisplays(int userId, String reason) {
synchronized (mGlobalLock) {
//一路调用到 RootActivityContainer 的startHomeOnDisplay()方法,参考[4.2]
return mRootActivityContainer.startHomeOnAllDisplays(userId, reason);
}
}
4.2 [RootActivityContainer.java] startHomeOnDisplay()
说明:在[4.1]中,获取的displayId为DEFAULT_DISPLAY, 首先通过getHomeIntent 来构建一个category为CATEGORY_HOME的Intent,表明是Home Activity;然后通过resolveHomeActivity()从系统所用已安装的引用中,找到一个符合HomeItent的Activity,最终调用startHomeActivity()来启动Activity
源码:
boolean startHomeOnDisplay(int userId, String reason, int displayId, boolean allowInstrumenting,
boolean fromHomeKey) {
...
if (displayId == DEFAULT_DISPLAY) {
//构建一个category为CATEGORY_HOME的Intent,表明是Home Activity,参考[4.2.1]
homeIntent = mService.getHomeIntent();
//通过PKMS从系统所用已安装的引用中,找到一个符合HomeItent的Activity参考[4.2.2]
aInfo = resolveHomeActivity(userId, homeIntent);
}
...
//启动Home Activity,参考[4.3]
mService.getActivityStartController().startHomeActivity(homeIntent, aInfo, myReason,
displayId);
return true;
}
4.2.1 [ActivityTaskManagerService.java] getHomeIntent()
说明:构建一个category为CATEGORY_HOME的Intent,表明是Home Activity。
Intent.CATEGORY_HOME = "android.intent.category.HOME"
这个category会在Launcher3的 AndroidManifest.xml中配置,表明是Home Acivity
源码:
Intent getHomeIntent() {
Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);
intent.setComponent(mTopComponent);
intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
//不是生产模式,add一个CATEGORY_HOME
if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
intent.addCategory(Intent.CATEGORY_HOME);
}
return intent;
}
4.2.2 [RootActivityContainer.java] resolveHomeActivity()
说明:通过Binder跨进程通知PackageManagerService从系统所用已安装的引用中,找到一个符合HomeItent的Activity
源码:
ActivityInfo resolveHomeActivity(int userId, Intent homeIntent) {
final int flags = ActivityManagerService.STOCK_PM_FLAGS;
final ComponentName comp = homeIntent.getComponent(); //系统正常启动时,component为null
ActivityInfo aInfo = null;
...
if (comp != null) {
// Factory test.
aInfo = AppGlobals.getPackageManager().getActivityInfo(comp, flags, userId);
} else {
//系统正常启动时,走该流程
final String resolvedType =
homeIntent.resolveTypeIfNeeded(mService.mContext.getContentResolver());
//resolveIntent做了两件事:1.通过queryIntentActivities来查找符合HomeIntent需求Activities
// 2.通过chooseBestActivity找到最符合Intent需求的Activity信息
final ResolveInfo info = AppGlobals.getPackageManager()
.resolveIntent(homeIntent, resolvedType, flags, userId);
if (info != null) {
aInfo = info.activityInfo;
}
}
...
aInfo = new ActivityInfo(aInfo);
aInfo.applicationInfo = mService.getAppInfoForUser(aInfo.applicationInfo, userId);
return aInfo;
}
4.3 [ActivityStartController.java ] startHomeActivity()
说明:正在的启动Home Activity入口。obtainStarter() 方法返回的是 ActivityStarter 对象,它负责 Activity 的启动,一系列 setXXX() 方法传入启动所需的各种参数,最后的 execute() 是真正的启动逻辑。另外如果home activity处于顶层的resume activity中,则Home Activity 将被初始化,但不会被恢复。并将保持这种状态,直到有东西再次触发它。我们需要进行另一次恢复。
源码:
void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason, int displayId) {
....
//返回一个 ActivityStarter 对象,它负责 Activity 的启动
//一系列 setXXX() 方法传入启动所需的各种参数,最后的 execute() 是真正的启动逻辑
//最后执行 ActivityStarter的execute方法
mLastHomeActivityStartResult = obtainStarter(intent, "startHomeActivity: " + reason)
.setOutActivity(tmpOutRecord)
.setCallingUid(0)
.setActivityInfo(aInfo)
.setActivityOptions(options.toBundle())
.execute(); //参考[4.3.1]
mLastHomeActivityStartRecord = tmpOutRecord[0];
final ActivityDisplay display =
mService.mRootActivityContainer.getActivityDisplay(displayId);
final ActivityStack homeStack = display != null ? display.getHomeStack() : null;
if (homeStack != null && homeStack.mInResumeTopActivity) {
//如果home activity 处于顶层的resume activity中,则Home Activity 将被初始化,但不会被恢复(以避免递归恢复),
//并将保持这种状态,直到有东西再次触发它。我们需要进行另一次恢复。
mSupervisor.scheduleResumeTopActivities();
}
}
4.3.1 [ActivityStarter.java] execute()
说明:在[4.3]中obtainStarter没有调用setMayWait的方法,因此mRequest.mayWait为false,走startActivity流程
源码:
int execute() {
...
if (mRequest.mayWait) {
return startActivityMayWait(...)
} else {
return startActivity(...) //参考[4.3.2]
}
...
}
4.3.2 [ActivityStarter.java] startActivity()
说明:延时布局,然后通过startActivityUnchecked()来处理启动标记 flag ,要启动的任务栈等,最后恢复布局
源码:
private int startActivity(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity, boolean restrictedBgActivity) {
...
try {
//延时布局
mService.mWindowManager.deferSurfaceLayout();
//调用 startActivityUnchecked ,一路调用到resumeFocusedStacksTopActivities(),参考[4.3.4]
result = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, doResume, options, inTask, outActivity, restrictedBgActivity);
} finally {
//恢复布局
mService.mWindowManager.continueSurfaceLayout();
}
...
}
4.3.3 [RootActivityContainer.java] resumeFocusedStacksTopActivities()
说明:获取栈顶的Activity,恢复它
源码:
boolean resumeFocusedStacksTopActivities(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
...
//如果秒表栈就是栈顶Activity,启动resumeTopActivityUncheckedLocked()
if (targetStack != null && (targetStack.isTopStackOnDisplay()
|| getTopDisplayFocusedStack() == targetStack)) {
result = targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
...
if (!resumedOnDisplay) {
// 获取 栈顶的 ActivityRecord
final ActivityStack focusedStack = display.getFocusedStack();
if (focusedStack != null) {
//最终调用startSpecificActivityLocked(),参考[4.3.4]
focusedStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}
}
}
}
4.3.4 [ActivityStackSupervisor.java] startSpecificActivityLocked()
说明:发布消息以启动进程,以避免在ATM锁保持的情况下调用AMS时可能出现死锁,最终调用到ATM的startProcess()
源码:
void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {
...
//发布消息以启动进程,以避免在ATM锁保持的情况下调用AMS时可能出现死锁
//最终调用到AMS的startProcess(),参考[4.3.5]
final Message msg = PooledLambda.obtainMessage(
ActivityManagerInternal::startProcess, mService.mAmInternal, r.processName,
r.info.applicationInfo, knownToBeDead, "activity", r.intent.getComponent());
mService.mH.sendMessage(msg);
...
}
4.3.5 [ActivityManagerService.java] startProcess()
说明:一路调用Process start(),最终到ZygoteProcess的attemptUsapSendArgsAndGetResult(),用来fork一个新的Launcher的进程
源码:
public void startProcess(String processName, ApplicationInfo info,
boolean knownToBeDead, String hostingType, ComponentName hostingName) {
..
//同步操作,避免死锁
synchronized (ActivityManagerService.this) {
//调用startProcessLocked,然后到 Process的start,最终到ZygoteProcess的attemptUsapSendArgsAndGetResult()
//用来fork一个新的Launcher的进程,参考[4.3.6]
startProcessLocked(processName, info, knownToBeDead, 0 /* intentFlags */,
new HostingRecord(hostingType, hostingName),
false /* allowWhileBooting */, false /* isolated */,
true /* keepIfLarge */);
}
...
}
调用栈如下:
4.3.6 [ZygoteProcess.java] attemptZygoteSendArgsAndGetResult()
说明:通过Socket连接Zygote进程,把之前组装的msg发给Zygote,其中processClass ="android.app.ActivityThread",通过Zygote进程来Fork出一个新的进程,并执行 "android.app.ActivityThread"的main方法
源码:
private Process.ProcessStartResult attemptZygoteSendArgsAndGetResult(
ZygoteState zygoteState, String msgStr) throws ZygoteStartFailedEx {
try {
//传入的zygoteState为openZygoteSocketIfNeeded(),里面会通过abi来检查是第一个zygote还是第二个
final BufferedWriter zygoteWriter = zygoteState.mZygoteOutputWriter;
final DataInputStream zygoteInputStream = zygoteState.mZygoteInputStream;
zygoteWriter.write(msgStr); //把应用进程的一些参数写给前面连接的zygote进程,包括前面的processClass ="android.app.ActivityThread"
zygoteWriter.flush(); //进入Zygote进程,处于阻塞状态, 参考[4.4]
//从socket中得到zygote创建的应用pid,赋值给 ProcessStartResult的对象
Process.ProcessStartResult result = new Process.ProcessStartResult();
result.pid = zygoteInputStream.readInt();
result.usingWrapper = zygoteInputStream.readBoolean();
if (result.pid < 0) {
throw new ZygoteStartFailedEx("fork() failed");
}
return result;
} catch (IOException ex) {
zygoteState.close();
Log.e(LOG_TAG, "IO Exception while communicating with Zygote - "
+ ex.toString());
throw new ZygoteStartFailedEx(ex);
}
}
4.4 第二阶段Zygote fork一个Launcher进程的阶段
说明:Zygote的启动过程我们前面有详细讲到过。SystemServer的AMS服务向启动Home Activity发起一个fork请求,Zygote进程通过Linux的fork函数,孵化出一个新的进程。
由于Zygote进程在启动时会创建Java虚拟机,因此通过fork而创建的Launcher程序进程可以在内部获取一个Java虚拟机的实例拷贝。fork采用copy-on-write机制,有些类如果不做改变,甚至都不用复制,子进程可以和父进程共享这部分数据,从而省去不少内存的占用。
fork过程,参考下图:
Zygote的调用栈如下:
4.4.1 [ZygoteInit.java] main()
说明:Zygote先fork出SystemServer进程,接着进入循环等待,用来接收Socket发来的消息,用来fork出其他应用进程,比如Launcher
源码:
public static void main(String argv[]) {
...
Runnable caller;
....
if (startSystemServer) {
//Zygote Fork出的第一个进程 SystmeServer
Runnable r = forkSystemServer(abiList, zygoteSocketName, zygoteServer);
if (r != null) {
r.run();
return;
}
}
...
//循环等待fork出其他的应用进程,比如Launcher
//最终通过调用processOneCommand()来进行进程的处理,参考[4.4.2]
caller = zygoteServer.runSelectLoop(abiList);
...
if (caller != null) {
caller.run(); //执行返回的Runnable对象,进入子进程
}
}
4.4.2 [ZygoteConnection.java] processOneCommand()
说明:通过forkAndSpecialize()来fork出Launcher的子进程,并执行handleChildProc,进入子进程的处理
源码:
Runnable processOneCommand(ZygoteServer zygoteServer) {
int pid = -1;
...
//Fork子进程,得到一个新的pid
/fork子进程,采用copy on write方式,这里执行一次,会返回两次
///pid=0 表示Zygote fork子进程成功
//pid > 0 表示子进程 的真正的PID
pid = Zygote.forkAndSpecialize(parsedArgs.mUid, parsedArgs.mGid, parsedArgs.mGids,
parsedArgs.mRuntimeFlags, rlimits, parsedArgs.mMountExternal, parsedArgs.mSeInfo,
parsedArgs.mNiceName, fdsToClose, fdsToIgnore, parsedArgs.mStartChildZygote,
parsedArgs.mInstructionSet, parsedArgs.mAppDataDir, parsedArgs.mTargetSdkVersion);
...
if (pid == 0) {
// in child, fork成功,第一次返回的pid = 0
...
//参考[4.4.3]
return handleChildProc(parsedArgs, descriptors, childPipeFd,
parsedArgs.mStartChildZygote);
} else {
//in parent
...
childPipeFd = null;
handleParentProc(pid, descriptors, serverPipeFd);
return null;
}
}
4.4.3 [ZygoteConnection.java] handleChildProc()
说明:进行子进程的操作,最终获得需要执行的ActivityThread的main()
源码:
private Runnable handleChildProc(ZygoteArguments parsedArgs, FileDescriptor[] descriptors,
FileDescriptor pipeFd, boolean isZygote) {
...
if (parsedArgs.mInvokeWith != null) {
...
throw new IllegalStateException("WrapperInit.execApplication unexpectedly returned");
} else {
if (!isZygote) {
// App进程将会调用到这里,执行目标类的main()方法
return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion,
parsedArgs.mRemainingArgs, null /* classLoader */);
} else {
return ZygoteInit.childZygoteInit(parsedArgs.mTargetSdkVersion,
parsedArgs.mRemainingArgs, null /* classLoader */);
}
}
}
zygoteInit 进行一些环境的初始化、启动Binder进程等操作:
public static final Runnable zygoteInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
RuntimeInit.commonInit(); //初始化运行环境
ZygoteInit.nativeZygoteInit(); //启动Binder线程池
//调用程序入口函数
return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
}
把之前传来的"android.app.ActivityThread" 传递给findStaticMain:
protected static Runnable applicationInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
...
// startClass: 如果AMS通过socket传递过来的是 ActivityThread
return findStaticMain(args.startClass, args.startArgs, classLoader);
}
通过反射,拿到ActivityThread的main()方法:
protected static Runnable findStaticMain(String className, String[] argv,
ClassLoader classLoader) {
Class cl;
try {
cl = Class.forName(className, true, classLoader);
} catch (ClassNotFoundException ex) {
throw new RuntimeException(
"Missing class when invoking static main " + className,
ex);
}
Method m;
try {
m = cl.getMethod("main", new Class[] { String[].class });
} catch (NoSuchMethodException ex) {
throw new RuntimeException(
"Missing static main on " + className, ex);
} catch (SecurityException ex) {
throw new RuntimeException(
"Problem getting static main on " + className, ex);
}
int modifiers = m.getModifiers();
if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
throw new RuntimeException(
"Main method is not public and static on " + className);
}
return new MethodAndArgsCaller(m, argv);
}
把反射得来的ActivityThread main()入口返回给ZygoteInit的main,通过caller.run()进行调用:
static class MethodAndArgsCaller implements Runnable {
/** method to call */
private final Method mMethod;
/** argument array */
private final String[] mArgs;
public MethodAndArgsCaller(Method method, String[] args) {
mMethod = method;
mArgs = args;
}
//调用ActivityThread的main()
public void run() {
try {
mMethod.invoke(null, new Object[] { mArgs });
} catch (IllegalAccessException ex) {
throw new RuntimeException(ex);
} catch (InvocationTargetException ex) {
Throwable cause = ex.getCause();
if (cause instanceof RuntimeException) {
throw (RuntimeException) cause;
} else if (cause instanceof Error) {
throw (Error) cause;
}
throw new RuntimeException(ex);
}
}
}
4.5 第三个阶段,Launcher在自己的进程中进行onCreate等后面的动作
从[4.4]可以看到,Zygote fork出了Launcher的进程,并把接下来的Launcher启动任务交给了ActivityThread来进行,接下来我们就从ActivityThread main()来分析Launcher的创建过程。
调用栈如下:
4.5.1 [ActivityThread.java] main()
说明:主线程处理, 创建ActivityThread对象,调用attach进行处理,最终进入Looper循环
源码:
public static void main(String[] args) {
// 安装选择性的系统调用拦截
AndroidOs.install();
...
//主线程处理
Looper.prepareMainLooper();
...
//之前SystemServer调用attach传入的是true,这里到应用进程传入false就行
ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);
...
//一直循环,如果退出,说明程序关闭
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
调用ActivityThread的attach进行处理
private void attach(boolean system, long startSeq) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
//应用进程启动,走该流程
...
RuntimeInit.setApplicationObject(mAppThread.asBinder());
//获取AMS的本地代理类
final IActivityManager mgr = ActivityManager.getService();
try {
//通过Binder调用AMS的attachApplication方法,参考[4.5.2]
mgr.attachApplication(mAppThread, startSeq);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
...
} else {
//通过system_server启动ActivityThread对象
...
}
// 为 ViewRootImpl 设置配置更新回调,
当系统资源配置(如:系统字体)发生变化时,通知系统配置发生变化
ViewRootImpl.ConfigChangedCallback configChangedCallback
= (Configuration globalConfig) -> {
synchronized (mResourcesManager) {
...
}
};
ViewRootImpl.addConfigCallback(configChangedCallback);
}
4.5.2 [ActivityManagerService.java] attachApplication()
说明:清除一些无用的记录,最终调用ActivityStackSupervisor.java的 realStartActivityLocked(),进行Activity的启动
源码:
public final void attachApplication(IApplicationThread thread, long startSeq) {
synchronized (this) {
//通过Binder获取传入的pid信息
int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid, callingUid, startSeq);
Binder.restoreCallingIdentity(origId);
}
}
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid, int callingUid, long startSeq) {
...
//如果当前的Application记录仍然依附到之前的进程中,则清理掉
if (app.thread != null) {
handleAppDiedLocked(app, true, true);
}·
//mProcessesReady这个变量在AMS的 systemReady 中被赋值为true,
//所以这里的normalMode也为true
boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
...
//上面说到,这里为true,进入StackSupervisor的attachApplication方法
//去真正启动Activity
if (normalMode) {
...
//调用ATM的attachApplication(),最终层层调用到ActivityStackSupervisor.java的 realStartActivityLocked()
//参考[4.5.3]
didSomething = mAtmInternal.attachApplication(app.getWindowProcessController());
...
}
...
return true;
}
4.5.3 [ActivityStackSupervisor.java] realStartActivityLocked()
说明:真正准备去启动Activity,通过clientTransaction.addCallback把LaunchActivityItem的obtain作为回调参数加进去,再调用
ClientLifecycleManager.scheduleTransaction()得到
LaunchActivityItem的execute()方法进行最终的执行
参考上面的第三阶段的调用栈流程
调用栈如下:
源码:
boolean realStartActivityLocked(ActivityRecord r, WindowProcessController proc,
boolean andResume, boolean checkConfig) throws RemoteException {
// 直到所有的 onPause() 执行结束才会去启动新的 activity
if (!mRootActivityContainer.allPausedActivitiesComplete()) {
...
return false;
}
try {
// Create activity launch transaction.
// 添加 LaunchActivityItem
final ClientTransaction clientTransaction = ClientTransaction.obtain(
proc.getThread(), r.appToken);
//LaunchActivityItem.obtain(new Intent(r.intent)作为回调参数
clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
System.identityHashCode(r), r.info,
// TODO: Have this take the merged configuration instead of separate global
// and override configs.
mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), r.compat,
r.launchedFromPackage, task.voiceInteractor, proc.getReportedProcState(),
r.icicle, r.persistentState, results, newIntents,
dc.isNextTransitionForward(), proc.createProfilerInfoIfNeeded(),
r.assistToken));
...
// 设置生命周期状态
final ActivityLifecycleItem lifecycleItem;
if (andResume) {
lifecycleItem = ResumeActivityItem.obtain(dc.isNextTransitionForward());
} else {
lifecycleItem = PauseActivityItem.obtain();
}
clientTransaction.setLifecycleStateRequest(lifecycleItem);
// Schedule transaction.
// 重点关注:调用 ClientLifecycleManager.scheduleTransaction(),得到上面addCallback的LaunchActivityItem的execute()方法
//参考[4.5.4]
mService.getLifecycleManager().scheduleTransaction(clientTransaction);
} catch (RemoteException e) {
if (r.launchFailed) {
// 第二次启动失败,finish activity
stack.requestFinishActivityLocked(r.appToken, Activity.RESULT_CANCELED, null,
"2nd-crash", false);
return false;
}
// 第一次失败,重启进程并重试
r.launchFailed = true;
proc.removeActivity(r);
throw e;
}
} finally {
endDeferResume();
}
...
return true;
}
4.5.4 [TransactionExecutor.java] execute()
说明:执行之前realStartActivityLocked()中的
clientTransaction.addCallback
源码:
[TransactionExecutor.java]
public void execute(ClientTransaction transaction) {
...
// 执行 callBack,参考上面的调用栈,执行回调方法,
//最终调用到ActivityThread的handleLaunchActivity()参考[4.5.5]
executeCallbacks(transaction);
// 执行生命周期状态
executeLifecycleState(transaction);
mPendingActions.clear();
}
4.5.5 [ActivityThread.java] handleLaunchActivity()
说明:主要干了两件事,第一件:初始化WindowManagerGlobal;第二件:调用performLaunchActivity方法
源码:
[ActivityThread.java]
public Activity handleLaunchActivity(ActivityClientRecord r,
PendingTransactionActions pendingActions, Intent customIntent) {
...
//初始化WindowManagerGlobal
WindowManagerGlobal.initialize();
...
//调用performLaunchActivity,来处理Activity,参考[4.5.6]
final Activity a = performLaunchActivity(r, customIntent);
..
return a;
}
4.5.6 [ActivityThread.java] performLaunchActivity()
说明:获取ComponentName、Context,反射创建Activity,设置Activity的一些内容,比如主题等; 最终调用callActivityOnCreate()来执行Activity的onCreate()方法
源码:
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
// 获取 ComponentName
ComponentName component = r.intent.getComponent();
...
// 获取 Context
ContextImpl appContext = createBaseContextForActivity(r);
Activity activity = null;
try {
// 反射创建 Activity
java.lang.ClassLoader cl = appContext.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state != null) {
r.state.setClassLoader(cl);
}
} catch (Exception e) {
...
}
try {
// 获取 Application
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
if (activity != null) {
...
//Activity的一些处理
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window, r.configCallback,
r.assistToken);
if (customIntent != null) {
activity.mIntent = customIntent;
}
...
int theme = r.activityInfo.getThemeResource();
if (theme != 0) {
// 设置主题
activity.setTheme(theme);
}
activity.mCalled = false;
// 执行 onCreate()
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
...
r.activity = activity;
}
//当前状态为ON_CREATE
r.setState(ON_CREATE);
...
} catch (SuperNotCalledException e) {
throw e;
} catch (Exception e) {
...
}
return activity;
}
callActivityOnCreate先执行activity onCreate的预处理,再去调用Activity的onCreate,最终完成Create创建后的内容处理
public void callActivityOnCreate(Activity activity, Bundle icicle,
PersistableBundle persistentState) {
prePerformCreate(activity); //activity onCreate的预处理
activity.performCreate(icicle, persistentState);//执行onCreate()
postPerformCreate(activity); //activity onCreate创建后的一些信息处理
}
performCreate()主要调用Activity的onCreate()
final void performCreate(Bundle icicle, PersistableBundle persistentState) {
...
if (persistentState != null) {
onCreate(icicle, persistentState);
} else {
onCreate(icicle);
}
...
}
至此,看到了我们最熟悉的Activity的onCreate(),Launcher的启动完成,Launcher被真正创建起来。
看到onCreate()后,进入到我们最熟悉的Activity的入口,Launcher的启动告一段落。整个Android的启动流程,我们也完整的分析完成。
Launcher的启动经过了三个阶段:
第一个阶段:SystemServer完成启动Launcher Activity的调用
第二个阶段:Zygote()进行Launcher进程的Fork操作
第三个阶段:进入ActivityThread的main(),完成最终Launcher的onCreate操作
下一节会来分析一下Android的进程创建过程以及Zygote的fork流程。
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