Android系统启动-SystemServer下篇

花门楼前见秋草，岂能贫贱相看老。这篇文章主要讲述Android系统启动-SystemServer下篇相关的知识，希望能为你提供帮助。
copy from ：http://gityuan.com/2016/02/20/android-system-server-2/

基于android 6.0的源码剖析，分析Android启动过程的system_server进程

frameworks/base/services/java/com/android/server/ - SystemServer.javaframeworks/base/services/core/java/com/android/server/ - SystemServiceManager.java - ServiceThread.java - am/ActivityManagerService.javaframeworks/base/core/java/android/app/ - ActivityThread.java - LoadedApk.java - ContextImpl.java

一. SystemServer启动上篇文章Android系统启动-systemServer上篇从Zygote一路启动到SystemServer的过程。简单回顾下，在RuntimeInit.java中invokeStaticMain方法通过创建并抛出异常ZygoteInit.MethodAndArgsCaller，在ZygoteInit.java中的main()方法会捕捉该异常，并调用caller.run()，再通过反射便会调用到SystemServer.main()方法，该方法主要执行流程：

SystemServer.main SystemServer.run createSystemContext startBootstrapServices(); startCoreServices(); startOtherServices(); Looper.loop();

接下来，从其main方法说起。
1.1 SystemServer.main

public final class SystemServer { ... public static void main(String[] args) { //先初始化SystemServer对象，再调用对象的run()方法，【见小节1.2】 new SystemServer().run(); } }

1.2 SystemServer.run

private void run() { //当系统时间比1970年更早，就设置当前系统时间为1970年 if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) { SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME); }//变更虚拟机的库文件，对于Android 6.0默认采用的是libart.so SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary()); if (SamplingProfilerIntegration.isEnabled()) { ... }//清除vm内存增长上限，由于启动过程需要较多的虚拟机内存空间 VMRuntime.getRuntime().clearGrowthLimit(); //设置内存的可能有效使用率为0.8 VMRuntime.getRuntime().setTargetHeapUtilization(0.8f); // 针对部分设备依赖于运行时就产生指纹信息，因此需要在开机完成前已经定义 Build.ensureFingerprintProperty(); //访问环境变量前，需要明确地指定用户 Environment.setUserRequired(true); //确保当前系统进程的binder调用，总是运行在前台优先级(foreground priority) BinderInternal.disableBackgroundScheduling(true); android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_FOREGROUND); android.os.Process.setCanSelfBackground(false); // 主线程looper就在当前线程运行 Looper.prepareMainLooper(); //加载android_servers.so库，该库包含的源码在frameworks/base/services/目录下 System.loadLibrary("android_servers"); //检测上次关机过程是否失败，该方法可能不会返回[见小节1.2.1] performPendingShutdown(); //初始化系统上下文【见小节1.3】 createSystemContext(); //创建系统服务管理 mSystemServiceManager = new SystemServiceManager(mSystemContext); //将mSystemServiceManager添加到本地服务的成员sLocalServiceObjects LocalServices.addService(SystemServiceManager.class, mSystemServiceManager); //启动各种系统服务 try { startBootstrapServices(); // 启动引导服务【见小节1.4】 startCoreServices(); // 启动核心服务【见小节1.5】 startOtherServices(); // 启动其他服务【见小节1.6】 } catch (Throwable ex) { Slog.e("System", "************ Failure starting system services", ex); throw ex; }//用于debug版本，将log事件不断循环地输出到dropbox（用于分析） if (StrictMode.conditionallyEnableDebugLogging()) { Slog.i(TAG, "Enabled StrictMode for system server main thread."); } //一直循环执行 Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); }

LocalServices通过用静态Map变量sLocalServiceObjects，来保存以服务类名为key，以具体服务对象为value的Map结构。
1.2.1 performPendingShutdown[– > SystemServer.java]

private void performPendingShutdown() { final String shutdownAction = SystemProperties.get( ShutdownThread.SHUTDOWN_ACTION_PROPERTY, ""); if (shutdownAction != null & & shutdownAction.length() > 0) { boolean reboot = (shutdownAction.charAt(0) == ‘1‘); final String reason; if (shutdownAction.length() > 1) { reason = shutdownAction.substring(1, shutdownAction.length()); } else { reason = null; } // 当"sys.shutdown.requested"值不为空,则会重启或者关机 ShutdownThread.rebootOrShutdown(null, reboot, reason); } }

1.3 createSystemContext
[– > SystemServer.java]

private void createSystemContext() { //创建system_server进程的上下文信息 ActivityThread activityThread = ActivityThread.systemMain(); mSystemContext = activityThread.getSystemContext(); //设置主题 mSystemContext.setTheme(android.R.style.Theme_DeviceDefault_Light_DarkActionBar); }

理解Application创建过程已介绍过createSystemContext()过程，该过程会创建对象有ActivityThread，Instrumentation, ContextImpl，LoadedApk，Application。
1.4 startBootstrapServices
[– > SystemServer.java]

private void startBootstrapServices() { //阻塞等待与installd建立socket通道 Installer installer = mSystemServiceManager.startService(Installer.class); //启动服务ActivityManagerService mActivityManagerService = mSystemServiceManager.startService( ActivityManagerService.Lifecycle.class).getService(); mActivityManagerService.setSystemServiceManager(mSystemServiceManager); mActivityManagerService.setInstaller(installer); //启动服务PowerManagerService mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class); //初始化power management mActivityManagerService.initPowerManagement(); //启动服务LightsService mSystemServiceManager.startService(LightsService.class); //启动服务DisplayManagerService mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class); //Phase100: 在初始化package manager之前，需要默认的显示. mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY); //当设备正在加密时，仅运行核心 String cryptState = SystemProperties.get("vold.decrypt"); if (ENCRYPTING_STATE.equals(cryptState)) { mOnlyCore = true; } else if (ENCRYPTED_STATE.equals(cryptState)) { mOnlyCore = true; }//启动服务PackageManagerService mPackageManagerService = PackageManagerService.main(mSystemContext, installer, mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore); mFirstBoot = mPackageManagerService.isFirstBoot(); mPackageManager = mSystemContext.getPackageManager(); //启动服务UserManagerService，新建目录/data/user/ ServiceManager.addService(Context.USER_SERVICE, UserManagerService.getInstance()); AttributeCache.init(mSystemContext); //设置AMS mActivityManagerService.setSystemProcess(); //启动传感器服务 startSensorService(); }

该方法所创建的服务：ActivityManagerService, PowerManagerService, LightsService, DisplayManagerService， PackageManagerService， UserManagerService， sensor服务.
1.5 startCoreServices

private void startCoreServices() { //启动服务BatteryService，用于统计电池电量，需要LightService. mSystemServiceManager.startService(BatteryService.class); //启动服务UsageStatsService，用于统计应用使用情况 mSystemServiceManager.startService(UsageStatsService.class); mActivityManagerService.setUsageStatsManager( LocalServices.getService(UsageStatsManagerInternal.class)); mPackageManagerService.getUsageStatsIfNoPackageUsageInfo(); //启动服务WebViewUpdateService mSystemServiceManager.startService(WebViewUpdateService.class); }

启动服务BatteryService，UsageStatsService，WebViewUpdateService。
1.6 startOtherServices
该方法比较长，有近千行代码，逻辑很简单，主要是启动一系列的服务，这里就不具体列举源码了，在第四节直接对其中的服务进行一个简单分类。

private void startOtherServices() { ... SystemConfig.getInstance(); mContentResolver = context.getContentResolver(); // resolver ... mActivityManagerService.installSystemProviders(); //provider mSystemServiceManager.startService(AlarmManagerService.class); // alarm // watchdog watchdog.init(context, mActivityManagerService); inputManager = new InputManagerService(context); // input wm = WindowManagerService.main(...); // window inputManager.start(); //启动input mDisplayManagerService.windowManagerAndInputReady(); ... mSystemServiceManager.startService(MOUNT_SERVICE_CLASS); // mount mPackageManagerService.performBootDexOpt(); // dexopt操作 ActivityManagerNative.getDefault().showBootMessage(...); //显示启动界面 ... statusBar = new StatusBarManagerService(context, wm); //statusBar //dropbox ServiceManager.addService(Context.DROPBOX_SERVICE, new DropBoxManagerService(context, new File("/data/system/dropbox"))); mSystemServiceManager.startService(JobSchedulerService.class); //JobScheduler lockSettings.systemReady(); //lockSettings//phase480 和phase500 mSystemServiceManager.startBootPhase(SystemService.PHASE_LOCK_SETTINGS_READY); mSystemServiceManager.startBootPhase(SystemService.PHASE_SYSTEM_SERVICES_READY); ... // 准备好window, power, package, display服务 wm.systemReady(); mPowerManagerService.systemReady(...); mPackageManagerService.systemReady(); mDisplayManagerService.systemReady(...); //重头戏[见小节2.1] mActivityManagerService.systemReady(new Runnable() { public void run() { ... } }); }

SystemServer启动各种服务中最后的一个环节便是AMS.systemReady()，详见ActivityManagerService启动过程.
到此, System_server主线程的启动工作总算完成, 进入Looper.loop()状态,等待其他线程通过handler发送消息到主线再处理.
二、服务启动阶段SystemServiceManager的startBootPhase()贯穿system_server进程的整个启动过程：

文章图片

其中PHASE_BOOT_COMPLETED=1000，该阶段是发生在Boot完成和home应用启动完毕。系统服务更倾向于监听该阶段，而不是注册广播ACTION_BOOT_COMPLETED，从而降低系统延迟。
各个启动阶段所在源码的大致位置：

public final class SystemServer {private void startBootstrapServices() { ... //phase100 mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY); ... }private void startCoreServices() { ... }private void startOtherServices() { ... //phase480 & & 500 mSystemServiceManager.startBootPhase(SystemService.PHASE_LOCK_SETTINGS_READY); mSystemServiceManager.startBootPhase(SystemService.PHASE_SYSTEM_SERVICES_READY); ... mActivityManagerService.systemReady(new Runnable() { public void run() { //phase550 mSystemServiceManager.startBootPhase( SystemService.PHASE_ACTIVITY_MANAGER_READY); ... //phase600 mSystemServiceManager.startBootPhase( SystemService.PHASE_THIRD_PARTY_APPS_CAN_START); } } } }

接下来再说说简单每个阶段的大概完成的工作：
2.1 Phase0创建四大引导服务:

ActivityManagerService
PowerManagerService
LightsService
DisplayManagerService

2.2 Phase100进入阶段PHASE_WAIT_FOR_DEFAULT_DISPLAY=100回调服务
onBootPhase(100)

DisplayManagerService

然后创建大量服务下面列举部分:

PackageManagerService
WindowManagerService
InputManagerService
NetworkManagerService
DropBoxManagerService
FingerprintService
LauncherAppsService
…

2.3 Phase480进入阶段PHASE_LOCK_SETTINGS_READY=480回调服务
onBootPhase(480)

DevicePolicyManagerService

阶段480后马上就进入阶段500.
2.4 Phase500PHASE_SYSTEM_SERVICES_READY=500，进入该阶段服务能安全地调用核心系统服务.
onBootPhase(500)

AlarmManagerService
JobSchedulerService
NotificationManagerService
BackupManagerService
UsageStatsService
DeviceIdleController
TrustManagerService
UiModeManagerService
BluetoothService
BluetoothManagerService
EthernetService
WifiP2pService
WifiScanningService
WifiService
RttService

各大服务执行systemReady():

WindowManagerService.systemReady():
PowerManagerService.systemReady():
PackageManagerService.systemReady():
DisplayManagerService.systemReady():

接下来就绪AMS.systemReady方法.
2.5 Phase550PHASE_ACTIVITY_MANAGER_READY=550， AMS.mSystemReady=true, 已准备就绪,进入该阶段服务能广播Intent; 但是system_server主线程并没有就绪.
onBootPhase(550)

MountService
TelecomLoaderService
UsbService
WebViewUpdateService
DockObserver
BatteryService

接下来执行: (AMS启动native crash监控, 加载WebView，启动SystemUi等),如下

mActivityManagerService.startObservingNativeCrashes();
WebViewFactory.prepareWebViewInSystemServer();
startSystemUi(context);
networkScoreF.systemReady();
networkManagementF.systemReady();
networkStatsF.systemReady();
networkPolicyF.systemReady();
connectivityF.systemReady();
audioserviceF.systemReady();
Watchdog.getInstance().start();

2.6 Phase600PHASE_THIRD_PARTY_APPS_CAN_START=600
onBootPhase(600)

JobSchedulerService
NotificationManagerService
BackupManagerService
AppWidgetService
GestureLauncherService
DreamManagerService
TrustManagerService
VoiceInteractionManagerService

接下来,各种服务的systemRunning过程:
WallpaperManagerService、InputMethodManagerService、LocationManagerService、CountryDetectorService、NetworkTimeUpdateService、CommonTimeManagementService、TextServicesManagerService、AssetAtlasService、InputManagerService、TelephonyRegistry、MediaRouterService、MmsServiceBroker这些服务依次执行其systemRunning()方法。
2.7 Phase1000在经过一系列流程，再调用AMS.finishBooting()时，则进入阶段Phase1000。
到此，系统服务启动阶段完成就绪，system_server进程启动完成则进入Looper.loop()状态，随时待命，等待消息队列MessageQueue中的消息到来，则马上进入执行状态。
三、服务类别
system_server进程，从源码角度划分为引导服务、核心服务、其他服务3类。以下这些系统服务的注册过程, 见Android系统服务的注册方式

引导服务(7个)：ActivityManagerService、PowerManagerService、LightsService、DisplayManagerService、PackageManagerService、UserManagerService、SensorService；
核心服务(3个)：BatteryService、UsageStatsService、WebViewUpdateService；
其他服务(70个+)：AlarmManagerService、VibratorService等。

合计总大约80个系统服务：

`ActivityManagerService`	`PackageManagerService`	`WindowManagerService`
`PowerManagerService`	`BatteryService`	`BatteryStatsService`
`DreamManagerService`	`DropBoxManagerService`	`SamplingProfilerService`
`UsageStatsService`	`DiskStatsService`	`DeviceStorageMonitorService`
SchedulingPolicyService	`AlarmManagerService`	DeviceIdleController
ThermalObserver	JobSchedulerService	`AccessibilityManagerService`
DisplayManagerService	LightsService	`GraphicsStatsService`
StatusBarManagerService	NotificationManagerService	WallpaperManagerService
UiModeManagerService	AppWidgetService	LauncherAppsService
TextServicesManagerService	ContentService	LockSettingsService
InputMethodManagerService	InputManagerService	`MountService`
FingerprintService	TvInputManagerService	DockObserver
NetworkManagementService	NetworkScoreService	`NetworkStatsService`
NetworkPolicyManagerService	ConnectivityService	BluetoothService
WifiP2pService	WifiService	WifiScanningService
AudioService	MediaRouterService	VoiceInteractionManagerService
MediaProjectionManagerService	MediaSessionService
DevicePolicyManagerService	PrintManagerService	`BackupManagerService`
`UserManagerService`	AccountManagerService	`TrustManagerService`
`SensorService`	LocationManagerService	VibratorService
CountryDetectorService	GestureLauncherService	PersistentDataBlockService
EthernetService	WebViewUpdateService	ClipboardService
TelephonyRegistry	TelecomLoaderService	NsdService
UpdateLockService	SerialService	SearchManagerService
CommonTimeManagementService	AssetAtlasService	ConsumerIrService
MidiServiceCameraService	TwilightService	RestrictionsManagerService
MmsServiceBroker	RttService	UsbService