本文主要是介绍ActivityManagerService源码分析（一），希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
前言：
AMS是Android系统服务中很重要的一个，他负责四大组件的启动、切换、调度、生命周期的管理等等，接下来我们根据AMS的启动来分析AMS的源码
1. SystemServer启动AMS
ActivityManagerService是在SystemServer.java中启动并注册的：
private void startBootstrapServices() {......// 启动AMS，见小节2.1mActivityManagerService = mSystemServiceManager.startService(ActivityManagerService.Lifecycle.class).getService();// 设置AMSmActivityManagerService.setSystemServiceManager(mSystemServiceManager);//安装App安装器mActivityManagerService.setInstaller(installer);......// 电源管理已经开启，在AMS中初始化PM，见小节3Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "InitPowerManagement");mActivityManagerService.initPowerManagement();Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);......// 设置应用实例，在系统进程开始的时候，见小节4mActivityManagerService.setSystemProcess();......}看源码可以看到（我没有贴出来），startBootstrapServices中启动并注册了很多其他的服务，比如：PowerManagerService，DisplayManagerService，LightsService，PackageManagerService，UserManagerService，SensorService(native)，这写服务彼此之间有依赖，所以都放在startBootstrapServices方法里面
2. 注册并启动
2.1 startService
文件：SystemServiceManager.java
public <T extends SystemService> T startService(Class<T> serviceClass) {try {final String name = serviceClass.getName();Slog.i(TAG, "Starting " + name);Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartService " + name);// 创建服务if (!SystemService.class.isAssignableFrom(serviceClass)) {throw new RuntimeException("Failed to create " + name+ ": service must extend " + SystemService.class.getName());}final T service;try {Constructor<T> constructor = serviceClass.getConstructor(Context.class);service = constructor.newInstance(mContext);} catch (InstantiationException ex) {throw new RuntimeException("Failed to create service " + name+ ": service could not be instantiated", ex);} catch (IllegalAccessException ex) {throw new RuntimeException("Failed to create service " + name+ ": service must have a public constructor with a Context argument", ex);} catch (NoSuchMethodException ex) {throw new RuntimeException("Failed to create service " + name+ ": service must have a public constructor with a Context argument", ex);} catch (InvocationTargetException ex) {throw new RuntimeException("Failed to create service " + name+ ": service constructor threw an exception", ex);}// 注册mServices.add(service);// 开始服务try {service.onStart();} catch (RuntimeException ex) {throw new RuntimeException("Failed to start service " + name+ ": onStart threw an exception", ex);}return service;} finally {Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);}}可以看出这方法的作用是创建并且开始一个服务，但是这个服务的类必须是SystemService的子类，于是我们需要传入带有ActivityManagerService的Lifecycle
2.2 Lifecycle
文件：SystemServiceManager.java
public static final class Lifecycle extends SystemService {private final ActivityManagerService mService;public Lifecycle(Context context) {super(context);// 构建一个新的AMS，见小节2.3mService = new ActivityManagerService(context);}@Overridepublic void onStart() {// 开始服务，2.1中的service.onStart()调用的就是它，见小节2.4mService.start();}public ActivityManagerService getService() {return mService;}}可以看出Lifecycle是继承SystemService的，并且在构造里构建了AMS，接下来我们来看看AMS的构建函数
2.3 AMS的构建函数
public ActivityManagerService(Context systemContext) {mContext = systemContext;mFactoryTest = FactoryTest.getMode();mSystemThread = ActivityThread.currentActivityThread();Slog.i(TAG, "Memory class: " + ActivityManager.staticGetMemoryClass());// 创建一个mHandlerThread线程，默认名是：ActivityManagermHandlerThread = new ServiceThread(TAG,android.os.Process.THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);mHandlerThread.start();// 创建一个基于ActivityManager线程的HandlermHandler = new MainHandler(mHandlerThread.getLooper());// 创建一个UiHandler线程mUiHandler = new UiHandler();// 用单例的方式创建一个名叫ActivityManager:kill的线程，并且创建一个killHandlerif (sKillHandler == null) {sKillThread = new ServiceThread(TAG + ":kill",android.os.Process.THREAD_PRIORITY_BACKGROUND, true /* allowIo */);sKillThread.start();// 用于杀死进程sKillHandler = new KillHandler(sKillThread.getLooper());}// 构建一个可以延时10秒的前台广播队列mFgBroadcastQueue = new BroadcastQueue(this, mHandler,"foreground", BROADCAST_FG_TIMEOUT, false);// 构建一个可以延时60秒的普通广播队列mBgBroadcastQueue = new BroadcastQueue(this, mHandler,"background", BROADCAST_BG_TIMEOUT, true);mBroadcastQueues[0] = mFgBroadcastQueue;mBroadcastQueues[1] = mBgBroadcastQueue;mServices = new ActiveServices(this);mProviderMap = new ProviderMap(this);mAppErrors = new AppErrors(mContext, this);// 新建一个data/system目录File dataDir = Environment.getDataDirectory();File systemDir = new File(dataDir, "system");systemDir.mkdirs();// 创建一个BatteryStatsService类mBatteryStatsService = new BatteryStatsService(systemDir, mHandler);// 把最新的数据写入硬盘mBatteryStatsService.scheduleWriteToDisk();mOnBattery = DEBUG_POWER ? true: mBatteryStatsService.getActiveStatistics().getIsOnBattery();mBatteryStatsService.getActiveStatistics().setCallback(this);// 创建进程统计服务类，并新建一个data/system/procstats目录mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats"));// 创建一个应用权限检查类，新建一个data/system/appops.xml文件，并注册对应的回调接口mAppOpsService = new AppOpsService(new File(systemDir, "appops.xml"), mHandler);mAppOpsService.startWatchingMode(AppOpsManager.OP_RUN_IN_BACKGROUND, null,new IAppOpsCallback.Stub() {@Override public void opChanged(int op, int uid, String packageName) {if (op == AppOpsManager.OP_RUN_IN_BACKGROUND && packageName != null) {if (mAppOpsService.checkOperation(op, uid, packageName)!= AppOpsManager.MODE_ALLOWED) {runInBackgroundDisabled(uid);}}}});mGrantFile = new AtomicFile(new File(systemDir, "urigrants.xml"));// 创建多用户控制器，user 0是第一个，同时也是唯一开机过程中运行的用户mUserController = new UserController(this);// 获取OpenGL版本，如果没有找到，则默认为0GL_ES_VERSION = SystemProperties.getInt("ro.opengles.version",ConfigurationInfo.GL_ES_VERSION_UNDEFINED);mTrackingAssociations = "1".equals(SystemProperties.get("debug.track-associations"));// 设置系统的一些默认配置信息mConfiguration.setToDefaults();mConfiguration.setLocales(LocaleList.getDefault());mConfigurationSeq = mConfiguration.seq = 1;// 初始化进程CPU跟踪器mProcessCpuTracker.init();// 解析/data/system/packages-compat.xml文件，当设备屏幕大小不满足APK所需要的大小，// 则从packages-compat.xml都去尺寸，用兼容的方式运行mCompatModePackages = new CompatModePackages(this, systemDir, mHandler);// 根据AMS传入规则，过滤一些IntentmIntentFirewall = new IntentFirewall(new IntentFirewallInterface(), mHandler);// 用来管理Activity栈mStackSupervisor = new ActivityStackSupervisor(this);// 解释怎样启动ActivitymActivityStarter = new ActivityStarter(this, mStackSupervisor);// 管理最近任务列表mRecentTasks = new RecentTasks(this, mStackSupervisor);//创建一个统计进程使用CPU情况的线程，名叫CpuTrackermProcessCpuThread = new Thread("CpuTracker") {@Overridepublic void run() {while (true) {try {try {synchronized(this) {final long now = SystemClock.uptimeMillis();long nextCpuDelay = (mLastCpuTime.get()+MONITOR_CPU_MAX_TIME)-now;long nextWriteDelay = (mLastWriteTime+BATTERY_STATS_TIME)-now;//Slog.i(TAG, "Cpu delay=" + nextCpuDelay// + ", write delay=" + nextWriteDelay);if (nextWriteDelay < nextCpuDelay) {nextCpuDelay = nextWriteDelay;}if (nextCpuDelay > 0) {mProcessCpuMutexFree.set(true);this.wait(nextCpuDelay);}}} catch (InterruptedException e) {}updateCpuStatsNow();} catch (Exception e) {Slog.e(TAG, "Unexpected exception collecting process stats", e);}}}};// watchdog添加对AMS的监控Watchdog.getInstance().addMonitor(this);Watchdog.getInstance().addThread(mHandler);......这个方法会在main thread中被唤醒，但是它需要通过各个handers和其他thread通信，所以要注意明确looper。该构造函数，里面是初始化一些变量，及创建了一些线程，大部分我都进行了注释。
2.4 start
文件：ActivityManagerService.java
private void start() {// 移除所有的进程组Process.removeAllProcessGroups();// 开始监控进程的CPU使用情况mProcessCpuThread.start();// 注册电池统计服务mBatteryStatsService.publish(mContext);// 注册应用权限检测服务mAppOpsService.publish(mContext);Slog.d("AppOps", "AppOpsService published");// 注册LocalService服务LocalServices.addService(ActivityManagerInternal.class, new LocalService());}启动ProcessCpuThread，注册电池统计服务，应用权限检测服务和LocalService，其中LocalService继承了ActivityManagerInternal。
小结：创建AMS，启动AMS
3. 初始化PM
3. initPowerManagement
文件：ActivityManagerService.java
public void initPowerManagement() {// Activity堆栈管理器和电池统计服务初始化PMmStackSupervisor.initPowerManagement();mBatteryStatsService.initPowerManagement();mLocalPowerManager = LocalServices.getService(PowerManagerInternal.class);PowerManager pm = (PowerManager)mContext.getSystemService(Context.POWER_SERVICE);mVoiceWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "*voice*");// 该唤醒锁为不计数锁，即无论acquire()多少次，一次release()就可以解锁mVoiceWakeLock.setReferenceCounted(false);}小结：这主要是在AMS中初始化PM
4. 设置应用实例
4.1 setSystemProcess
文件：ActivityManagerService.java
public void setSystemProcess() {try {// 以下都是想ServiceManager注册服务ServiceManager.addService(Context.ACTIVITY_SERVICE, this, true); // 注册AMS自己ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats); // 注册进程统计服务ServiceManager.addService("meminfo", new MemBinder(this)); // 注册内存信息的服务ServiceManager.addService("gfxinfo", new GraphicsBinder(this)); // 注册输出渲染信息的服务ServiceManager.addService("dbinfo", new DbBinder(this)); // 注册输出数据库信息的服务// MONITOR_CPU_USAGE默认为trueif (MONITOR_CPU_USAGE) {ServiceManager.addService("cpuinfo", new CpuBinder(this)); // 输出进程使用CPU的情况}ServiceManager.addService("permission", new PermissionController(this)); // 注册权限管理ServiceManager.addService("processinfo", new ProcessInfoService(this)); // 注册进程信息// 查询名为android的应用信息ApplicationInfo info = mContext.getPackageManager().getApplicationInfo("android", STOCK_PM_FLAGS | MATCH_SYSTEM_ONLY);// 调用installSystemApplicationInfo ，见小节4.2mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());// synchronized (this) {// 创建一个ProcessRecord对象 ，见小节4.5ProcessRecord 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();}} catch (PackageManager.NameNotFoundException e) {throw new RuntimeException("Unable to find android system package", e);}}4.2 installSystemApplicationInfo
文件：ActivityThread.java
public void installSystemApplicationInfo(ApplicationInfo info, ClassLoader classLoader) {synchronized (this) {// 看SystemService中创建的ContextIml的installSystemApplicationInfo，见小节4.3getSystemContext().installSystemApplicationInfo(info, classLoader);// give ourselves a default profilermProfiler = new Profiler();}}4.3 ContextIml.installSystemApplicationInfo
文件：ContextImpl.java
void installSystemApplicationInfo(ApplicationInfo info, ClassLoader classLoader) {// 调用的是LoadeApk里面的installSystemApplicationInfo，见小节4.4mPackageInfo.installSystemApplicationInfo(info, classLoader);}4.4 LoadeApk.installSystemApplicationInfo
文件：LoadeApk.java
void installSystemApplicationInfo(ApplicationInfo info, ClassLoader classLoader) {// 断言只有packageName为android才能使用assert info.packageName.equals("android");mApplicationInfo = info;mClassLoader = classLoader;}将ApplicationInfo加入到LoadeApk中，因为SystemService创建LoadeApk时，PKMS并没有完成对手机中文件的解析
4.5 AMS进程管理
文件：ActivityManagerService.java
......synchronized (this) {// 调用进程管理函数，见4.6ProcessRecord app = newProcessRecordLocked(info, info.processName, false, 0);app.persistent = true;app.pid = MY_PID;app.maxAdj = ProcessList.SYSTEM_ADJ;// 将SystemServer对应的ApplicationThread保存到ProcessRecord中app.makeActive(mSystemThread.getApplicationThread(), mProcessStats);synchronized (mPidsSelfLocked) {// 根据ProcessRecord的pid，将ProcessRecord存在mPidsSelfLocked中mPidsSelfLocked.put(app.pid, app);}updateLruProcessLocked(app, false, null);updateOomAdjLocked();}......
4.6 newProcessRecordLocked
文件：ActivityManagerService.java
final ProcessRecord newProcessRecordLocked(ApplicationInfo info, String customProcess,boolean isolated, int isolatedUid) {String proc = customProcess != null ? customProcess : info.processName;BatteryStatsImpl stats = mBatteryStatsService.getActiveStatistics();final int userId = UserHandle.getUserId(info.uid);int uid = info.uid;// isolated为falseif (isolated) {......}// 创建一个进程记录对象，见小节4.7final ProcessRecord r = new ProcessRecord(stats, info, proc, uid);// 判断是否为常驻的进程if (!mBooted && !mBooting&& userId == UserHandle.USER_SYSTEM&& (info.flags & PERSISTENT_MASK) == PERSISTENT_MASK) {r.persistent = true;}// 将ProcessRecord保存在AMS里的mProcessNames里addProcessNameLocked(r);return r;}4.7 ProcessRecord
文件：ProcessRecord.java
ProcessRecord(BatteryStatsImpl _batteryStats, ApplicationInfo _info,String _processName, int _uid) {mBatteryStats = _batteryStats;info = _info;isolated = _info.uid != _uid;uid = _uid;userId = UserHandle.getUserId(_uid);processName = _processName;pkgList.put(_info.packageName, new ProcessStats.ProcessStateHolder(_info.versionCode));maxAdj = ProcessList.UNKNOWN_ADJ;curRawAdj = setRawAdj = ProcessList.INVALID_ADJ;curAdj = setAdj = verifiedAdj = ProcessList.INVALID_ADJ;persistent = false;removed = false;lastStateTime = lastPssTime = nextPssTime = SystemClock.uptimeMillis();}这主要是保存一些ProcessRecord里面的属性。
小结：第四节的主要作用就是将一些服务注册到ServiceManger中，包括AMS自己；然后将framework-res-.apk中applicationInfo信息加入到SystemServeice生成的LoadedApk中，同时构建SystemService对应的ProcessRecord，最后通过addProcessNameLocked(r)来把SystemService加入AMS的管理中来。
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