Android系统启动-SystemServer下篇
frameworks/base/services/java/com/android/server/
- SystemServer.java
frameworks/base/services/core/java/com/android/server/
- SystemServiceManager.java
- ServiceThread.java
- am/ActivityManagerService.java
frameworks/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：
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 Phase500
PHASE_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 Phase550
PHASE_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 Phase600
PHASE_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 |
Service类别众多，其中表中加粗项是指博主挑选的较重要或者较常见的Service，并且在本博客中已经展开或者计划展开讲解的Service，当然如果有精力会讲解更多service，后续再更新。