之前讲Android的View的绘制原理和流程的时候，讲到过在Android调用setContentView之后，Android调用了一个prepreTravle的方法,这里面就提到了ActivityManagerService。
ActivityManagerService提供的主要功能：
（1）统一调度各应用程序的Activity
（2）内存管理
（3）进程管理
上一篇我们分析Android启动过程的文章中我们分析到了SystemServer，当时我们只是简单的描述了下，Android启动过程分析，我们还是来看一张启动的流程图，
System Server代码位于：//frameworks\base\services\java\com\android\server\SystemServer.java
我们来看一段启动的代码：
private void run() {
// 准备SystemServer运行环境:设置线程优先级，创建主线层Looper，ActivityThread和SystemContext
android.os.Process.setThreadPriority();
Looper.prepareMainLooper();
// 创建systemserver上进程的ActivityThread和SystemContext
createSystemContext();
// 增加SystemServiceManager：统一管理system services的创建，启动和生命周期，多用户切换
mSystemServiceManager = new SystemServiceManager(mSystemContext);
// Start services.
// 1.创建AMS
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
// Start the Power Manager service
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
// Start the package manager service
mPackageManagerService = PackageManagerService.main();
// 2.将SystemServer进程可加到AMS中调度管理
mActivityManagerService.setSystemProcess();
// 3.将相关provider运行在systemserver进程中：SettingsProvider
mActivityManagerService.installSystemProviders();
//
final Watchdog watchdog = Watchdog.getInstance();
watchdog.init(context, mActivityManagerService);
// Start Window Manager
wm = WindowManagerService.main();
// 4.直接保存wms对象，与WMS交互
mActivityManagerService.setWindowManager(wm);
// 5.通过WMS 弹出“正在启动应用”框
// R.string.android_upgrading_starting_apps
ActivityManagerNative.getDefault().showBootMessage();
// 6. AMS作为Framework核心，做好准备就绪后就开始启动应用层，和对AMS有依赖的服务
mActivityManagerService.systemReady(new Runnable(){
//启动SystemUI
startSystemUi(context);
//启动WatchDog监控核心服务状态
Watchdog.getInstance().start();
//
mmsServiceF.systemRunning();
});
// Loop forever.
Looper.loop();
}
上面的6个步骤就是SystemServer中关于AMS的调用，完成AMS的创建和系统的初始化，以及与WMS交互等流程。
一、ActivityManagerService 创建过程
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
通过SystemServiceManager这样一个模板类来创建运行在SystemServer中的Framework服务。并将创建的服务统一保存在队列管理。
public ActivityManagerService(Context systemContext) {
// 1.系统Context 和 ActivityThread （将systemserver进程作为应用进程管理）
mContext = systemContext;
mFactoryTest = FactoryTest.getMode();
mSystemThread = ActivityThread.currentActivityThread();
// 2.AMS工作的线程和Handler，处理显示相关的UiHandler ---》知识点HandlerThread和Handler
mHandlerThread = new ServiceThread(TAG,
android.os.Process.THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
mHandlerThread.start();
mHandler = new MainHandler(mHandlerThread.getLooper());
mUiHandler = new UiHandler();
// 3. 广播队列BroadcastQueue初始化：前台广播队列和后台广播队列
mFgBroadcastQueue = new BroadcastQueue(this, mHandler,"foreground", BROADCAST_FG_TIMEOUT, false);
mBgBroadcastQueue = new BroadcastQueue(this, mHandler,"background", BROADCAST_BG_TIMEOUT, true);
mBroadcastQueues[0] = mFgBroadcastQueue;
mBroadcastQueues[1] = mBgBroadcastQueue;
// 4. Service 和 Provider 管理
mServices = new ActiveServices(this);
mProviderMap = new ProviderMap(this);
// 5.系统数据存放目录：/data/system/
File dataDir = Environment.getDataDirectory();
File systemDir = new File(dataDir, "system");
systemDir.mkdirs();
// 电池状态信息，进程状态 和 应用权限管理
mBatteryStatsService = new BatteryStatsService(systemDir, mHandler);
mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats"));
mAppOpsService = new AppOpsService(new File(systemDir, "appops.xml"), mHandler);
// 6.多用户管理
mStartedUsers.put(UserHandle.USER_OWNER, new UserState(UserHandle.OWNER, true));
mUserLru.add(UserHandle.USER_OWNER);
updateStartedUserArrayLocked();
// 7.最近任务，Activity，Task管理
mRecentTasks = new RecentTasks(this);
mStackSupervisor = new ActivityStackSupervisor(this, mRecentTasks);
mTaskPersister = new TaskPersister(systemDir, mStackSupervisor, mRecentTasks);
// 创建一个新线程，用于监控和定时更新系统CPU信息，30分钟更新一次CPU和电池信息
mProcessCpuTracker.init();
mProcessCpuThread = new Thread("CpuTracker") {}
// 加入Watchdog监控起来
Watchdog.getInstance().addMonitor(this);
Watchdog.getInstance().addThread(mHandler);
}
二、将SystemServer进程可加到AMS中调度管理
mActivityManagerService.setSystemProcess();
mActivityManagerService将system扔到ams统一管理和调度
public void setSystemProcess() {
// 将服务加入到ServiceManager中
ServiceManager.addService(Context.ACTIVITY_SERVICE, this, true);
ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
ServiceManager.addService("meminfo", new MemBinder(this));
ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
ServiceManager.addService("dbinfo", new DbBinder(this));
// 设置application info LoadedApkinfo 有关 framework-res.apk
ApplicationInfo info = mContext.getPackageManager().getApplicationInfo(
"android", STOCK_PM_FLAGS);
mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());
//给SystemServer进程创建ProcessRecord，adj值，就是将SystemServer进程加入到AMS进程管理机制中，跟应用进程一致
synchronized (this) {
ProcessRecord app = newProcessRecordLocked(info, info.processName, false, 0);
app.persistent = true;
app.pid = MY_PID;
app.maxAdj = ProcessList.SYSTEM_ADJ;
app.makeActive(mSystemThread.getApplicationThread(), mProcessStats);
synchronized (mPidsSelfLocked) {
mPidsSelfLocked.put(app.pid, app);
}
updateLruProcessLocked(app, false, null);
updateOomAdjLocked();
}
}
这一步就是给SystemServer进程创建ProcessRecord，adj值，就是将SystemServer进程加入到AMS进程管理。
三、创建运行在SystemServer进程中Provider
mActivityManagerService.installSystemProviders();
取出进程名为"system"，user_id为SYSTEM_UID的进程信息 ，生成运行在system进程中的providerInfo，并交给上下文的Provider。这段代码的任务就是查询与安装Content Provider并且发布，其中查询出来的provider为SettingsProvider
public final void installSystemProviders() {
List<ProviderInfo> providers;
synchronized (this) {
//取出进程名为"system"，user_id为SYSTEM_UID的进程信息
ProcessRecord app = mProcessNames.get("system", Process.SYSTEM_UID);
//生成运行在system进程中的providerInfo，表示一个Content Provider。
providers = generateApplicationProvidersLocked(app);
if (providers != null) {
for (int i=providers.size()-1; i>=0; i--) {
ProviderInfo pi = (ProviderInfo)providers.get(i);
//过滤掉非系统apk
if ((pi.applicationInfo.flags&ApplicationInfo.FLAG_SYSTEM) == 0) {
Slog.w(TAG, "Not installing system proc provider " + pi.name
+ ": not system .apk");
providers.remove(i);
}
}
}
}
if (providers != null) {
//安装provider
mSystemThread.installSystemProviders(providers);
}
//监听Settings数据库变化。
mCoreSettingsObserver = new CoreSettingsObserver(this);
//mUsageStatsService.monitorPackages();
四、 AMS systemReady过程
mActivityManagerService.systemReady();
发送ACTION_PRE_BOOT_COMPLETE方法，清理启动的persistent进程，读取Settings配置，运行runnable接口，启动SystemUI，启动persistent应用程序，启动home，发送ACTION_BOOT_COMPLETE广播
public void systemReady(final Runnable goingCallback) {
synchronized(this) {
if (mSystemReady) {
goingCallback.run();
}
……
// 1.升级相关处理：发送PRE_BOOT_COMPLETED广播 等待升级处理完成才能继续
// Check to see if there are any update receivers to run.
if (!mDidUpdate) {
// 等待升级完成，否则直接返回
if (mWaitingUpdate) {
return;
}
// 发送PRE_BOOT_COMPLETED广播
final ArrayList<ComponentName> doneReceivers = new ArrayList<ComponentName>();
mWaitingUpdate = deliverPreBootCompleted(new Runnable() {
// 等待所有接收PRE_BOOT_COMPLETED广播者处理完毕
public void run() {
synchronized (ActivityManagerService.this) {
mDidUpdate = true;
}
showBootMessage(mContext.getText(
R.string.android_upgrading_complete),
false);
// 将系统版本号和处理过的广播写入文件：/data/system/called_pre_boots.dat文件
writeLastDonePreBootReceivers(doneReceivers);
// 继续systemReady流程
systemReady(goingCallback);
}
}, doneReceivers, UserHandle.USER_OWNER);
if (mWaitingUpdate) {
return;
}
mDidUpdate = true;
}
mSystemReady = true;
}
// 2. 收集已经启动的进程并杀死，除过persistent常驻进程
ArrayList<ProcessRecord> procsToKill = null;
synchronized(mPidsSelfLocked) {
for (int i=mPidsSelfLocked.size()-1; i>=0; i--) {
ProcessRecord proc = mPidsSelfLocked.valueAt(i);
if (!isAllowedWhileBooting(proc.info)){
if (procsToKill == null) {
procsToKill = new ArrayList<ProcessRecord>();
}
procsToKill.add(proc);
}
}
}
synchronized(this) {
if (procsToKill != null) {
for (int i=procsToKill.size()-1; i>=0; i--) {
ProcessRecord proc = procsToKill.get(i);
Slog.i(TAG, "Removing system update proc: " + proc);
removeProcessLocked(proc, true, false, "system update done");
}
}
// Now that we have cleaned up any update processes, we
// are ready to start launching real processes and know that
// we won't trample on them any more.
mProcessesReady = true;
}
// 3.系统准备好后回调传入的Runnable：
if (goingCallback != null) goingCallback.run();
// 4. 发送账户启动的广播，涉及多用户
long ident = Binder.clearCallingIdentity();
Intent intent = new Intent(Intent.ACTION_USER_STARTED);
broadcastIntentLocked(intent);
intent = new Intent(Intent.ACTION_USER_STARTING);
broadcastIntentLocked(intent);
Binder.restoreCallingIdentity(ident);
// 5. 启动桌面Home Activity
mBooting = true;
startHomeActivityLocked(mCurrentUserId, "systemReady");
mStackSupervisor.resumeTopActivitiesLocked();
}
参考：
http://www.cnblogs.com/bastard/p/5770573.html
