概述
该篇基于AndroidQ，主要介绍系统启动中的 AMS(ActivityManagerService)的启动过程。
AMS对四大组件(AndroidQ将activity移到了ActivityTaskManagerService中，但也和AMS相关联)进行管理和调度。同时，AMS也对进程、电池、内存、权限等进行管理。
AMS的启动过程 和 结束 部分，主要跟踪的代码过程，加以简单说明。代码中添加了注释，可做参考，有点长。如果只想简单了解下，可以直接看下最后的 简单总结 部分。
AMS相关目录结构
AMS代码主要在下面几个目录(AndroidQ上AMS相关部分功能移到了wm下)：
frameworks/base/core/java/android/app/
frameworks/base/services/core/java/com/android/server/am/
frameworks/base/services/core/java/com/android/server/wm/
下面具体看下几个重要文件
frameworks/base/core/java/android/app/下：
- Activity.java：所有Activity的父类。
- ActivityManager.java：AMS的客户端，提供给用户可调用的api。
- ActivityThread.java：应用进程的主线程类，一般即UI线程。
frameworks/base/services/core/java/com/android/server/am/下：
- ActiveServices.java：控制service的启动、重启等。
- ProcessRecord.java：记录每个进程的信息。
frameworks/base/services/core/java/com/android/server/wm/下：
- ActivityRecord.java：activity对象信息的记录。
- ActivityStack.java/ActivityStackSupervisor.java：管理activity生命周期及堆栈等。
- TaskRecord.java：任务栈记录，管理一个任务的应用activity
- ActivityTaskManagerService.java/ActivityTaskManagerInternal.java：管理activity的启动和调度。
文末附上了一个图片，是ActivityStack、ActivityStackSupervisor、TaskRecord、ActivityRecord、ProcessRecord之间的关系。
AMS的启动过程
系统启动、AMS起点之前
系统启动后Zygote进程第一个fork出SystemServer进程，进入到SystemServer:main()->run()->startBootstrapServices() 启动引导服务，进而完成AMS的启动。
下面是fork出SystemServer的过程，有不少地方需要进一步学习，了解下不做说明。ZygoteInit.java:main()->forkSystemServer()->Zygote.java:forkSystemServer()->nativeForkSystemServer()->com_android_internal_os_Zygote.cpp:com_android_internal_os_Zygote_nativeForkSystemServer()->ZygoteInit.java->handleSystemServerProcess()。
直接从SystemServer的run()看：
//frameworks/base/services/java/com/android/server/SystemServer.java
private void run() {
try {
createSystemContext();
}
try {
traceBeginAndSlog("StartServices");
startBootstrapServices();
startCoreServices();
startOtherServices();
SystemServerInitThreadPool.shutdown();
}
}
private void createSystemContext() {
ActivityThread activityThread = ActivityThread.systemMain();
//初始化系统context，并设置主题
mSystemContext = activityThread.getSystemContext();
mSystemContext.setTheme(DEFAULT_SYSTEM_THEME);
//初始化SystemUi context,并设置主题
final Context systemUiContext = activityThread.getSystemUiContext();
systemUiContext.setTheme(DEFAULT_SYSTEM_THEME);
}createSystemContext()创建了两个上下文，系统context和SystemUi context。这两个挺重要，会传入AMS中，这里就是它们创建的地方。
接下来看下上面创建两个上下文时的systemMain()，这个也很重要。
//ActivityThread.java
@UnsupportedAppUsage
public static ActivityThread systemMain() {
// The system process on low-memory devices do not get to use hardware
// accelerated drawing, since this can add too much overhead to the
// process.
if (!ActivityManager.isHighEndGfx()) {
ThreadedRenderer.disable(true);
} else {
ThreadedRenderer.enableForegroundTrimming();
}
ActivityThread thread = new ActivityThread();
thread.attach(true, 0);
return thread;
}
@UnsupportedAppUsage
ActivityThread() {
mResourcesManager = ResourcesManager.getInstance();
}
@UnsupportedAppUsage
private void attach(boolean system, long startSeq) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
.......
} else {
......
try {
mInstrumentation = new Instrumentation();
mInstrumentation.basicInit(this);
ContextImpl context = ContextImpl.createAppContext(
this, getSystemContext().mPackageInfo);
mInitialApplication = context.mPackageInfo.makeApplication(true, null);
mInitialApplication.onCreate();
}
......
}
.......
}ActivityThread是当前进程的主线程。SystemServer初始化时ActivityThread.systemMain()创建的是系统进程(SystemServer进程)的主线程。
构造函数是获取ResourcesManager的单例对象。
attach()这里走的是系统进程(应用启动也会走，那时system为false，走的时应用进程)，这里创建了几个重要的对象Instrumentation、Context、Application。
Instrumentation：很重要的一个基类，会优先实例化，允许检测系统与应用所有交互。应用中AndroidManifest.xml的标签可以定义其实现。
Context：上下文，应用运行环境的全局信息。这里创建的是一个LoadedApk(packagename是android，即framework-res.apk)，以此获取了Context对象。(具体可追踪ContextImpl.createAppContext())。
Application：保存应用的全局状态。
AMS查看起点
这里从startBootstrapServices()作为AMS启动的起点开始查看
//frameworks/base/services/java/com/android/server/SystemServer.java
private void startBootstrapServices() {
......
// TODO: Might need to move after migration to WM.
//part 0
ActivityTaskManagerService atm = mSystemServiceManager.startService(
ActivityTaskManagerService.Lifecycle.class).getService();
//part 1
mActivityManagerService = ActivityManagerService.Lifecycle.startService(
mSystemServiceManager, atm);
//part 2
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
//part 3
mActivityManagerService.setInstaller(installer);
// Now that the power manager has been started, let the activity manager
// initialize power management features.
//part 4
mActivityManagerService.initPowerManagement();
// Set up the Application instance for the system process and get started.
//part 5
mActivityManagerService.setSystemProcess();
// Complete the watchdog setup with an ActivityManager instance and listen for reboots
// Do this only after the ActivityManagerService is properly started as a system process
//part 6
watchdog.init(mSystemContext, mActivityManagerService);
}注意上面的几个部分(part0-part6)，是其中mActivityManagerService相关的，依次来具体看看，了解AMS的启动过程。
part 0：mSystemServiceManager.startService(ActivityTaskManagerService.Lifecycle.class).getService()
这句和ActivityManagerService.Lifecycle.startService()里执行过程(part 1中)是一样的，这里不详细说明，当看part 1部分就能知道。
这句创建了ActivityTaskManagerService对象，并调用了ActivityTaskManagerService中的start()方法启动服务。
ActivityTaskManagerService是Android 10新引入的变化，也是系统服务，用来管理Activity启动和调度，包括其容器(task、stacks、displays等)。这篇主要关于AMS的启动，因此ActivityTaskManagerService这里不赘述。
Android 10将原先AMS中对activity的管理和调度移到了ActivityTaskManagerService中，位置放到了wm下(见上面完整路径)，因此AMS负责四大组件中另外3个(service, broadcast, contentprovider)的管理和调度。
ActivityTaskManagerService.java上的注释说明：
System service for managing activities and their containers (task, stacks, displays,... ).
part 1：ActivityManagerService.Lifecycle.startService()
//ActivityManagerService.java
public static final class Lifecycle extends SystemService {
private final ActivityManagerService mService;
private static ActivityTaskManagerService sAtm;
public Lifecycle(Context context) {
super(context);
mService = new ActivityManagerService(context, sAtm);
}
public static ActivityManagerService startService(
SystemServiceManager ssm, ActivityTaskManagerService atm) {
sAtm = atm;
return ssm.startService(ActivityManagerService.Lifecycle.class).getService();
}
@Override
public void onStart() {
mService.start();
}
public ActivityManagerService getService() {
return mService;
}这里的Lifecycle是AMS的内部类。ActivityManagerService.Lifecycle.startService()最终返回的是mService，即创建的AMS对象。
接着来具体看下这个过程的实现，ActivityManagerService.Lifecycle.startService()进入SystemServiceManager类的startService()，继续看
//frameworks/base/services/core/java/com/android/server/SystemServiceManager.java
public <T extends SystemService> T startService(Class<T> serviceClass) {
try {
final String name = serviceClass.getName();
// Create the service.
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);
} ......
startService(service);
return service;
}
}
public void startService(@NonNull final SystemService service) {
// Register it.
mServices.add(service);
// Start it.
long time = SystemClock.elapsedRealtime();
try {
service.onStart();
} catch (RuntimeException ex) {
......
}
warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart");
}SystemServiceManager中通过反射，调用了ActivityManagerService.Lifecycle的构造方法，然后startService(service) 中最终调用了service.onStart()，即ActivityManagerService.Lifecycle.onStart()。
题外话，这里有几个稍微注意下：
- isAssignableFrom与instanceof：
Class1.isAssignableFrom(Class2)：都是Class类型 表示类或接口，判断Class1是否是Class2的父类或父接口，或者相同。
也可以简单看作：父类.class.isAssignableFrom(子类.class)。
oo instanceof TypeName：oo是实例对象，TypeName是具体类名或接口名。判断oo是否是TypeName的子类或接口实现。
也可以简单看作：子类实例 instanceof 父类类型。 - warnIfTooLong()中，时间elapsedRealtime()是包含深度睡眠的设备启动时间，具体在Handler消息机制有提过。另外这里的warn时间是SERVICE_CALL_WARN_TIME_MS -- 50ms。
接着需要看两点：通过反射调用ActivityManagerService.Lifecycle的构造方法，主要new ActivityManagerService() 创建AMS对象，干了些什么需要了解；ActivityManagerService.Lifecycle.onStart()就是直接调用AMS的start()方法；
new ActivityManagerService()
// Note: This method is invoked on the main thread but may need to attach various
// handlers to other threads. So take care to be explicit about the looper.
public ActivityManagerService(Context systemContext, ActivityTaskManagerService atm) {
LockGuard.installLock(this, LockGuard.INDEX_ACTIVITY);
mInjector = new Injector();
//系统上下文，是在SystemServer进程fork出来后通过createSystemContext()创建的，即与SystemServer进程是一一致
mContext = systemContext;
mFactoryTest = FactoryTest.getMode();
//系统进程的主线程 sCurrentActivityThread，这里是systemMain()中创建的ActivityThread对象。即也与SystemServer一样的。
mSystemThread = ActivityThread.currentActivityThread();
mUiContext = mSystemThread.getSystemUiContext();
Slog.i(TAG, "Memory class: " + ActivityManager.staticGetMemoryClass());
mHandlerThread = new ServiceThread(TAG,
THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
mHandlerThread.start();
//处理AMS消息的handle
mHandler = new MainHandler(mHandlerThread.getLooper());
//UiHandler对应于Android中的Ui线程
mUiHandler = mInjector.getUiHandler(this);
mProcStartHandlerThread = new ServiceThread(TAG + ":procStart",
THREAD_PRIORITY_FOREGROUND, false /* allowIo */);
mProcStartHandlerThread.start();
mProcStartHandler = new Handler(mProcStartHandlerThread.getLooper());
mConstants = new ActivityManagerConstants(mContext, this, mHandler);
final ActiveUids activeUids = new ActiveUids(this, true /* postChangesToAtm */);
mProcessList.init(this, activeUids);
mLowMemDetector = new LowMemDetector(this);
mOomAdjuster = new OomAdjuster(this, mProcessList, activeUids);
// Broadcast policy parameters
final BroadcastConstants foreConstants = new BroadcastConstants(
Settings.Global.BROADCAST_FG_CONSTANTS);
foreConstants.TIMEOUT = BROADCAST_FG_TIMEOUT;//10s
final BroadcastConstants backConstants = new BroadcastConstants(
Settings.Global.BROADCAST_BG_CONSTANTS);
backConstants.TIMEOUT = BROADCAST_BG_TIMEOUT;//60s
final BroadcastConstants offloadConstants = new BroadcastConstants(
Settings.Global.BROADCAST_OFFLOAD_CONSTANTS);
offloadConstants.TIMEOUT = BROADCAST_BG_TIMEOUT;
// by default, no "slow" policy in this queue
offloadConstants.SLOW_TIME = Integer.MAX_VALUE;
mEnableOffloadQueue = SystemProperties.getBoolean(
"persist.device_config.activity_manager_native_boot.offload_queue_enabled", false);
//创建几种广播相关对象，前台广播、后台广播、offload暂不了解TODO。
mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
"foreground", foreConstants, false);
mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
"background", backConstants, true);
mOffloadBroadcastQueue = new BroadcastQueue(this, mHandler,
"offload", offloadConstants, true);
mBroadcastQueues[0] = mFgBroadcastQueue;
mBroadcastQueues[1] = mBgBroadcastQueue;
mBroadcastQueues[2] = mOffloadBroadcastQueue;
// 创建ActiveServices对象，管理 ServiceRecord
mServices = new ActiveServices(this);
// 创建ProviderMap对象，管理ContentProviderRecord
mProviderMap = new ProviderMap(this);
mPackageWatchdog = PackageWatchdog.getInstance(mUiContext);
mAppErrors = new AppErrors(mUiContext, this, mPackageWatchdog);
final File systemDir = SystemServiceManager.ensureSystemDir();
// TODO: Move creation of battery stats service outside of activity manager service.
mBatteryStatsService = new BatteryStatsService(systemContext, systemDir,
BackgroundThread.get().getHandler());
mBatteryStatsService.getActiveStatistics().readLocked();
mBatteryStatsService.scheduleWriteToDisk();
mOnBattery = DEBUG_POWER ? true
: mBatteryStatsService.getActiveStatistics().getIsOnBattery();
mBatteryStatsService.getActiveStatistics().setCallback(this);
mOomAdjProfiler.batteryPowerChanged(mOnBattery);
mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats"));
mAppOpsService = mInjector.getAppOpsService(new File(systemDir, "appops.xml"), mHandler);
mUgmInternal = LocalServices.getService(UriGrantsManagerInternal.class);
mUserController = new UserController(this);
mPendingIntentController = new PendingIntentController(
mHandlerThread.getLooper(), mUserController);
if (SystemProperties.getInt("sys.use_fifo_ui", 0) != 0) {
mUseFifoUiScheduling = true;
}
mTrackingAssociations = "1".equals(SystemProperties.get("debug.track-associations"));
mIntentFirewall = new IntentFirewall(new IntentFirewallInterface(), mHandler);
//得到ActivityTaskManagerService的对象，调用ATM.initialize
mActivityTaskManager = atm;
mActivityTaskManager.initialize(mIntentFirewall, mPendingIntentController,
DisplayThread.get().getLooper());
mAtmInternal = LocalServices.getService(ActivityTaskManagerInternal.class);
mProcessCpuThread = new Thread("CpuTracker") {
......
};
mHiddenApiBlacklist = new HiddenApiSettings(mHandler, mContext);
//加入Watchdog的监控
Watchdog.getInstance().addMonitor(this);
Watchdog.getInstance().addThread(mHandler);
// bind background threads to little cores
// this is expected to fail inside of framework tests because apps can't touch cpusets directly
// make sure we've already adjusted system_server's internal view of itself first
updateOomAdjLocked(OomAdjuster.OOM_ADJ_REASON_NONE);
try {
Process.setThreadGroupAndCpuset(BackgroundThread.get().getThreadId(),
Process.THREAD_GROUP_SYSTEM);
Process.setThreadGroupAndCpuset(
mOomAdjuster.mAppCompact.mCompactionThread.getThreadId(),
Process.THREAD_GROUP_SYSTEM);
} catch (Exception e) {
Slog.w(TAG, "Setting background thread cpuset failed");
}
}AMS的构造方法，主要完成一些对象的构造及变量的初始化，可以看下上面的注释。
- 三大组件的(service、broadcast、provider)管理和调度(activity移到了ActivityTaskManagerService中，但此处也绑定了ActivityTaskManagerService对象)。
- 监控内存、电池、权限(可以了解下appops.xml)以及性能相关的对象或变量。mLowMemDetector、mBatteryStatsService、mProcessStats、mAppOpsService、mProcessCpuThread等。
AMS的start()
private void start() {
//移除所有的进程组
removeAllProcessGroups();
//启动CPU监控线程
mProcessCpuThread.start();
//注册电池、权限管理相关服务
mBatteryStatsService.publish();
mAppOpsService.publish(mContext);
Slog.d("AppOps", "AppOpsService published");
LocalServices.addService(ActivityManagerInternal.class, new LocalService());
mActivityTaskManager.onActivityManagerInternalAdded();
mUgmInternal.onActivityManagerInternalAdded();
mPendingIntentController.onActivityManagerInternalAdded();
// Wait for the synchronized block started in mProcessCpuThread,
// so that any other access to mProcessCpuTracker from main thread
// will be blocked during mProcessCpuTracker initialization.
try {
mProcessCpuInitLatch.await();
} catch (InterruptedException e) {
Slog.wtf(TAG, "Interrupted wait during start", e);
Thread.currentThread().interrupt();
throw new IllegalStateException("Interrupted wait during start");
}
}start()主要：
- 移除所有进程组，复位进程后，启动CPU监控线程。mProcessCpuThread在前面构造函数中创建的线程。
- 注册电池、权限管理的相关服务
- LocalService只能本进程使用，不可跨进程。
part 2:mActivityManagerService.setSystemServiceManager(mSystemServiceManager)
ActivityManagerService.java:
public void setSystemServiceManager(SystemServiceManager mgr) {
mSystemServiceManager = mgr;
}很简单，将SystemServer.java中创建的SystemServiceManager对象mSystemServiceManager 设置到了AMS中。
part 3:mActivityManagerService.setInstaller(installer)
ActivityManagerService.java:
public void setInstaller(Installer installer) {
mInstaller = installer;
}同样，将SystemServer.java中创建的Installer对象installer设置到AMS中。
part 4:mActivityManagerService.initPowerManagement()
ActivityManagerService.java:
public void initPowerManagement() {
mActivityTaskManager.onInitPowerManagement();
mBatteryStatsService.initPowerManagement();
mLocalPowerManager = LocalServices.getService(PowerManagerInternal.class);
}在前面创建AMS过程，mActivityTaskManager、mBatteryStatsService对象已创建 相关服务已注册。这里初始化电源管理的功能。
part 5:mActivityManagerService.setSystemProcess()
public void setSystemProcess() {
try {
//注册服务activity
ServiceManager.addService(Context.ACTIVITY_SERVICE, this, /* allowIsolated= */ true,
DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PRIORITY_NORMAL | DUMP_FLAG_PROTO);
//注册服务procstats，进程状态
ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
//注册服务meminfo，内存信息
ServiceManager.addService("meminfo", new MemBinder(this), /* allowIsolated= */ false,
DUMP_FLAG_PRIORITY_HIGH);
//注册服务gfxinfo，图像信息
ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
//注册服务dbinfo，数据库信息
ServiceManager.addService("dbinfo", new DbBinder(this));
if (MONITOR_CPU_USAGE) {
//注册服务cpuinfo，cpu信息
ServiceManager.addService("cpuinfo", new CpuBinder(this),
/* allowIsolated= */ false, DUMP_FLAG_PRIORITY_CRITICAL);
}
//注册服务permission和processinfo，权限和进程信息
ServiceManager.addService("permission", new PermissionController(this));
ServiceManager.addService("processinfo", new ProcessInfoService(this));
//获取“android”应用的ApplicationInfo，并装载到mSystemThread
ApplicationInfo info = mContext.getPackageManager().getApplicationInfo(
"android", STOCK_PM_FLAGS | MATCH_SYSTEM_ONLY);
mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());
//创建ProcessRecord维护进程的相关信息
synchronized (this) {
ProcessRecord app = mProcessList.newProcessRecordLocked(info, info.processName,
false,
0,
new HostingRecord("system"));
app.setPersistent(true);
app.pid = MY_PID;//
app.getWindowProcessController().setPid(MY_PID);
app.maxAdj = ProcessList.SYSTEM_ADJ;
app.makeActive(mSystemThread.getApplicationThread(), mProcessStats);
mPidsSelfLocked.put(app);//
mProcessList.updateLruProcessLocked(app, false, null);
updateOomAdjLocked(OomAdjuster.OOM_ADJ_REASON_NONE);
}
} catch (PackageManager.NameNotFoundException e) {
throw new RuntimeException(
"Unable to find android system package", e);
}
// Start watching app ops after we and the package manager are up and running.
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);
}
}
}
});
}这个方法 设置系统进程，AMS的setSystemProcess主要：
- 注册一些服务:activity、procstats、meminfo、gfxinfo、dbinfo、cpuinfo、permission、processinfo
关于服务的注册涉及binder相关内容，可以参考Binder机制 - 在起点部分，attach()过程获取Context对象时通过ContextImpl.createAppContext()创建了一个LoadedApk(packagename是android，即framework-res.apk)。
这里获取包名为“android”的应用的ApplicationInfo对象，并将该ApplicationInfo信息安装设置到SystemThread(系统进程主线程)。即可以理解，系统也是一个特殊的应用。 - 创建ProcessRecord维护进程的相关信息，这里MY_PID即为SystemServer进程ID。
- 启动 检测应用运行和交互。
part 6:watchdog.init(mSystemContext, mActivityManagerService)
初始化看门狗，AMS实列作为参数设置进入。
结束
这个过程，即系统完成启动，作为结束大致看下(已算不属于AMS的启动了，是在AMS启动之后)。我们平时接触比较多的，launcher、systemui都是在这个过程完成启动的，最后发送开机广播ACTION_BOOT_COMPLETED。
下面大致看下。
最开始讲过在SystemServer的run()中，有
traceBeginAndSlog("StartServices");
startBootstrapServices();
startCoreServices();
startOtherServices();上面讲到的都是startBootstrapServices()，AMS的启动在其中。最后，当引导服务、核心服务、其他服务都完成后，会调用AMS中的systemReady()方法。
SystemServer.java:
private void startOtherServices() {
mActivityManagerService.installSystemProviders();
// Now that SettingsProvider is ready, reactivate SQLiteCompatibilityWalFlags
SQLiteCompatibilityWalFlags.reset();
......
mActivityManagerService.systemReady(() -> {
......//goingCallback
}, BOOT_TIMINGS_TRACE_LOG);
}systemReady()
ActivityManagerService.java:
public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {
traceLog.traceBegin("PhaseActivityManagerReady");
synchronized(this) {
//第一次进入为false
if (mSystemReady) {
......
}
//关键服务等待systemReady，继续完成一些初始化或进一步的工作
mLocalDeviceIdleController
= LocalServices.getService(DeviceIdleController.LocalService.class);
mActivityTaskManager.onSystemReady();
// Make sure we have the current profile info, since it is needed for security checks.
mUserController.onSystemReady();
mAppOpsService.systemReady();
mSystemReady = true;
}
......
//mPidsSelfLocked中保留了当前正在运行的所有进程信息
ArrayList<ProcessRecord> procsToKill = null;
synchronized(mPidsSelfLocked) {
for (int i=mPidsSelfLocked.size()-1; i>=0; i--) {
ProcessRecord proc = mPidsSelfLocked.valueAt(i);
//已启动的进程，若进程没有FLAG_PERSISTENT标志，则会被加入到procsToKill中
if (!isAllowedWhileBooting(proc.info)){
if (procsToKill == null) {
procsToKill = new ArrayList<ProcessRecord>();
}
procsToKill.add(proc);
}
}
}
//关闭procsToKill中的所有进程
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);
mProcessList.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.
//到这里系统准备完毕
mProcessesReady = true;
}
Slog.i(TAG, "System now ready");
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_AMS_READY, SystemClock.uptimeMillis());
mAtmInternal.updateTopComponentForFactoryTest();
mAtmInternal.getLaunchObserverRegistry().registerLaunchObserver(mActivityLaunchObserver);
watchDeviceProvisioning(mContext);
retrieveSettings();
mUgmInternal.onSystemReady();
final PowerManagerInternal pmi = LocalServices.getService(PowerManagerInternal.class);
if (pmi != null) {
pmi.registerLowPowerModeObserver(ServiceType.FORCE_BACKGROUND_CHECK,
state -> updateForceBackgroundCheck(state.batterySaverEnabled));
updateForceBackgroundCheck(
pmi.getLowPowerState(ServiceType.FORCE_BACKGROUND_CHECK).batterySaverEnabled);
} else {
Slog.wtf(TAG, "PowerManagerInternal not found.");
}
//运行goingCallback，SystemServer调用时传入的
if (goingCallback != null) goingCallback.run();
// Check the current user here as a user can be started inside goingCallback.run() from
// other system services.
final int currentUserId = mUserController.getCurrentUserId();
......
final boolean bootingSystemUser = currentUserId == UserHandle.USER_SYSTEM;
if (bootingSystemUser) {
mSystemServiceManager.startUser(currentUserId);
}
synchronized (this) {
// Only start up encryption-aware persistent apps; once user is
// unlocked we'll come back around and start unaware apps
startPersistentApps(PackageManager.MATCH_DIRECT_BOOT_AWARE);//FLX
// Start up initial activity.
mBooting = true;
// Enable home activity for system user, so that the system can always boot. We don't
// do this when the system user is not setup since the setup wizard should be the one
// to handle home activity in this case.
if (UserManager.isSplitSystemUser() &&
Settings.Secure.getInt(mContext.getContentResolver(),
Settings.Secure.USER_SETUP_COMPLETE, 0) != 0) {
ComponentName cName = new ComponentName(mContext, SystemUserHomeActivity.class);
try {
AppGlobals.getPackageManager().setComponentEnabledSetting(cName,
PackageManager.COMPONENT_ENABLED_STATE_ENABLED, 0,
UserHandle.USER_SYSTEM);
} catch (RemoteException e) {
throw e.rethrowAsRuntimeException();
}
}
if (bootingSystemUser) {
//启动launcher的Activity.
mAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");
}
mAtmInternal.showSystemReadyErrorDialogsIfNeeded();
//发送一些广播ACTION_USER_STARTED ACTION_USER_STARTING
if (bootingSystemUser) {
......
traceLog.traceEnd(); // ActivityManagerStartApps
traceLog.traceEnd(); // PhaseActivityManagerReady
}
}
boolean isAllowedWhileBooting(ApplicationInfo ai) {
return (ai.flags&ApplicationInfo.FLAG_PERSISTENT) != 0;
}主要关注几步：
- 关键服务等继续完成一些初始化或进一步工作
- 已启动的进程，若进程没有FLAG_PERSISTENT标志，则会被kill掉
- 运行goingCallback，即调用时传入的
- 启动launcher的Activity，即桌面应用
- 发送一些广播ACTION_USER_STARTED ACTION_USER_STARTING。
注：开机向导在这里可以在这里跳过，注意 watchDeviceProvisioning(mContext)和Settings.Secure.USER_SETUP_COMPLETE属性。
goingCallback
//SystemServer.java:
traceBeginAndSlog("StartActivityManagerReadyPhase");
//启动阶段：550
mSystemServiceManager.startBootPhase(
SystemService.PHASE_ACTIVITY_MANAGER_READY);
traceEnd();
traceBeginAndSlog("StartObservingNativeCrashes");
try {
//监测Native Crash
mActivityManagerService.startObservingNativeCrashes();
} catch (Throwable e) {
reportWtf("observing native crashes", e);
}
traceEnd();
// No dependency on Webview preparation in system server. But this should
// be completed before allowing 3rd party
final String WEBVIEW_PREPARATION = "WebViewFactoryPreparation";
Future<?> webviewPrep = null;
if (!mOnlyCore && mWebViewUpdateService != null) {
webviewPrep = SystemServerInitThreadPool.get().submit(() -> {
Slog.i(TAG, WEBVIEW_PREPARATION);
TimingsTraceLog traceLog = new TimingsTraceLog(
SYSTEM_SERVER_TIMING_ASYNC_TAG, Trace.TRACE_TAG_SYSTEM_SERVER);
traceLog.traceBegin(WEBVIEW_PREPARATION);
ConcurrentUtils.waitForFutureNoInterrupt(mZygotePreload, "Zygote preload");
mZygotePreload = null;
//启动WebView相关
mWebViewUpdateService.prepareWebViewInSystemServer();
traceLog.traceEnd();
}, WEBVIEW_PREPARATION);
}
if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) {
traceBeginAndSlog("StartCarServiceHelperService");
mSystemServiceManager.startService(CAR_SERVICE_HELPER_SERVICE_CLASS);
traceEnd();
}
traceBeginAndSlog("StartSystemUI");
try {
//启动SystemUi
startSystemUi(context, windowManagerF);//FLX
} catch (Throwable e) {
reportWtf("starting System UI", e);
}
traceEnd();
// Wait for all packages to be prepared
mPackageManagerService.waitForAppDataPrepared();
//启动阶段：600
mSystemServiceManager.startBootPhase(
SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);
traceEnd();这里几个注意的
- startBootPhase，启动阶段。这里是550，600。这个表面大致启动的阶段，有助启动了解，具体看下面解释。
- 在550阶段，启动了SystemUi。
SystemService.java:
/*
* Boot Phases
*/
public static final int PHASE_WAIT_FOR_DEFAULT_DISPLAY = 100; // maybe should be a dependency?
/**
* After receiving this boot phase, services can obtain lock settings data.
*/
public static final int PHASE_LOCK_SETTINGS_READY = 480;
/**
* After receiving this boot phase, services can safely call into core system services
* such as the PowerManager or PackageManager.
*/
public static final int PHASE_SYSTEM_SERVICES_READY = 500;
/**
* After receiving this boot phase, services can safely call into device specific services.
*/
public static final int PHASE_DEVICE_SPECIFIC_SERVICES_READY = 520;
/**
* After receiving this boot phase, services can broadcast Intents.
*/
public static final int PHASE_ACTIVITY_MANAGER_READY = 550;
/**
* After receiving this boot phase, services can start/bind to third party apps.
* Apps will be able to make Binder calls into services at this point.
*/
public static final int PHASE_THIRD_PARTY_APPS_CAN_START = 600;
/**
* After receiving this boot phase, services can allow user interaction with the device.
* This phase occurs when boot has completed and the home application has started.
* System services may prefer to listen to this phase rather than registering a
* broadcast receiver for ACTION_BOOT_COMPLETED to reduce overall latency.
*/
public static final int PHASE_BOOT_COMPLETED = 1000;当桌面启动完成后，发送开机广播ACTION_BOOT_COMPLETED。(这里不赘述，可以从Launcher的resume阶段开始，调用AMS.finishBooting()方法发送)
简单总结
大致总结下AMS的启动。
- 系统启动后Zygote进程第一个fork出SystemServer进程
- SystemServer->run()->createSystemContext()：创建了系统的ActivityThread对象，运行环境mSystemContext、systemUiContext。
- SystemServer->run()->startBootstrapServices()->ActivityManagerService.Lifecycle.startService()：AMS在引导服务启动方法中，通过构造函数
new ActivityManagerService()进行了一些对象创建和初始化(除activity外3大组件的管理和调度对象创建；内存、电池、权限、性能、cpu等的监控等相关对象创建)，start()启动服务(移除进程组、启动cpu线程、注册权限、电池等服务)。 - SystemServer->run()->startBootstrapServices()->setSystemServiceManager()、setInstaller()、initPowerManagement()、setSystemProcess()：AMS创建后进行了一系列相关的初始化和设置。
setSystemProcess()：将framework-res.apk的信息加入到SystemServer进程的LoadedApk中，并创建了SystemServer进程的ProcessRecord，加入到mPidsSelfLocked，由AMS统一管理。 - SystemServer->run()->startOtherServices()：AMS启动后的后续工作，主要调用systemReady()和运行调用时传入的goingCallback。
systemReady()/goingCallback：各种服务或进程等AMS启动完成后需进一步完成的工作及系统相关初始化。 桌面应用在systemReady()方法中启动，systemui在goingCallback中完成。当桌面应用启动完成后，发送开机广播ACTION_BOOT_COMPLETED，到此为止。
最后附上一个图片，网上不少地方可以看见，几个类的关系很清晰。
善始者实繁，克终者盖寡。 ---不足或不对的地方欢迎指正。
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