android 开机启动流程分析（16）Launcher启动
系列文章解读&说明：
Android开机启动流程的分析主要分为以下部分：
（01）init之前启动说明
（02）init的启动流程分析
（03）init启动中关键进程 uevent & watchdog
（04）init启动中关键服务-属性服务
（05）SE Android 的解读
（06）init.rc解析流程
（07）action队列分析
（08）无限循环的处理
（09）bootchart 解读
（10）init 部分整体总结 --总结性说明{关键：思维导图重构 & 流程说明}
（11）Zygote启动分析
（12）SystemServer启动分析
（13）Zygote的分裂
（14）SystemServer WatchDog解读
（15）SystemServer部分服务解读
（16）Launcher启动
本模块分享的内容：Launcher启动
本章关键点总结 & 说明：
这里因为整体的导图太大，因此截取一部分 ，方便大家看的清楚：
在上图中关注➕“launcher启动”部分即可。同时，下面的图是开机启动流程分析 持续迭代的效果，可放大观看。
在SystemServer启动后，SystemServer又启动了AMS，同时在SystemServer中关键方法 startOtherServices 中
private void startOtherServices() {
//...
final AudioService audioServiceF = audioService;
mActivityManagerService.systemReady(new Runnable() {//这里会回调
@Override
public void run() {
Slog.i(TAG, "Making services ready");
mSystemServiceManager.startBootPhase(
SystemService.PHASE_ACTIVITY_MANAGER_READY);
try {
mActivityManagerService.startObservingNativeCrashes();
} catch (Throwable e) {
reportWtf("observing native crashes", e);
}
Slog.i(TAG, "WebViewFactory preparation");
WebViewFactory.prepareWebViewInSystemServer();
try {
startSystemUi(context);
} catch (Throwable e) {
reportWtf("starting System UI", e);
}
//...
try {
if (mmsServiceF != null) mmsServiceF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying MmsService running", e);
}
}
}); 1 这里专注AMS的SystemReady方法，实现如下：
public void systemReady(final Runnable goingCallback) {
synchronized(this) {
if (mSystemReady) {
// If we're done calling all the receivers, run the next "boot phase" passed in
// by the SystemServer
if (goingCallback != null) {
goingCallback.run();
}
return;
}
//...
/**startHomeActivityLocked调用栈
mStackSupervisor.startHomeActivity(intent, aInfo, reason);
moveHomeStackTaskToTop
startActivityLocked，这里接下来启动Activity的启动流程
*/
startHomeActivityLocked(mCurrentUserId, "systemReady");
//...
}
}这里在startHomeActivityLocked之后 便开始 执行 Activity的启动流程了,因为这里涉及的函数调用层数比较多，这里整理了一下startHomeActivityLocked的调用栈，如下所示：
/**startHomeActivityLocked调用栈*/
ActivityStackSupervisor:
mStackSupervisor.startHomeActivity(intent, aInfo, reason);
moveHomeStackTaskToTop->startActivityLocked，这里接下来启动Activity的启动流程
startActivityUncheckedLocked
resumeTopActivityLocked
-------------------------------------------------------
ActivityStack:->targetStack.startActivityLocked
mStackSupervisor.resumeTopActivitiesLocked
targetStack.resumeTopActivityLocked
resumeTopActivityInnerLocked
---------------------------------------
ActivityStackSupervisor:
mStackSupervisor.startSpecificActivityLocked
mService.getProcessRecordLocked
realStartActivityLocked
mService.startProcessLocked //创建 ActivityThread线程在这里，最后 调用的 startProcessLocked方法，目的就是 创建ActivityThread线程
2 创建ActivityThread线程流程如下：
mService.startProcessLocked //创建 ActivityThread线程
Process.start
startViaZygote
zygoteSendArgsAndGetResult3 最后在ActivityThread 启动后，执行main方法，分析如下：
public static void main(String[] args) {
SamplingProfilerIntegration.start();
CloseGuard.setEnabled(false);
Environment.initForCurrentUser();
// Set the reporter for event logging in libcore
EventLogger.setReporter(new EventLoggingReporter());
Security.addProvider(new AndroidKeyStoreProvider());
// Make sure TrustedCertificateStore looks in the right place for CA certificates
final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
TrustedCertificateStore.setDefaultUserDirectory(configDir);
Process.setArgV0("");
//创建looper对象，与本线程绑定，在activity或service或dialog中可以随便使用handler是这个线程在后台
Looper.prepareMainLooper();
//创建ActicityThread对象实例,当new ActivityThread()进行时，其成员变量ApplicationThread同时被创建
ActivityThread thread = new ActivityThread();
/**进行attach回调，调用栈如下：
mgr.attachApplication(mAppThread);
这里走的是binder通信->call AMS:attachApplication->attachApplicationLocked
*/
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
} 4 这里最为关键的一个步骤是attach，这里详细分析下：
private final boolean attachApplicationLocked(IApplicationThread thread, int pid) {
ProcessRecord app;
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
app = mPidsSelfLocked.get(pid);
}
} else {
app = null;
}
//...
app.makeActive(thread, mProcessStats);
//...
try {
//...
thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
app.instrumentationUiAutomationConnection, testMode, enableOpenGlTrace,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(mConfiguration), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked());
updateLruProcessLocked(app, false, null);
app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();
} catch (Exception e) {
// ...
return false;
}
//...
// See if the top visible activity is waiting to run in this process...
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {
//...
}
}
//...
return true;
}这里代码做了大部分的删减，主要表明这里做了4件事情，分别是
- PID->ProcessRecord
- thread->注册app记录
- thread与PID绑定
- call mStackSupervisor.attachApplicationLocked->realStartActivityLocked
通过attach，ActivityThread的ApplicationThread.scheduleResumeActivity触发显示，到此 Launcher 的Activity也就启动并显示出来了