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本篇文章主要介绍 Android 开发中 SystemServer进程启动 部分知识点，通过阅读本篇文章，您将收获以下内容:
一、SystemServer 启动的服务有哪些
二、SystemServer启动总体流程概述
三、SystemServer 如何启动，是谁启动的？
四、 SystemServer 启动入门 main 方法
五、SystemServer Run 方法初始与启动
六、SystemServer 的引导服务有哪些
七、SystemServer 的核心服务有哪些
八、SystemServer 的其他服务有哪些
一、SystemServer 启动的服务有哪些
SystemServer 主要启动 ActivityManagerService、PackageManagerService、WindowManagerService、LightsService、LightsService、BatteryService、TelephonyRegistry、RecoverySystemService 等等,主要分三大类，后文会详细列举。
SystemServer 启动的服务 作用如下：
二、SystemServer启动总体流程概述
SystemServer 代码路径:
\alps\frameworks\base\services\java\com\android\server\SystemServer.java
三、SystemServer 如何启动，是谁启动的？
SystemServer是通过Zygote 启动的，在ZygoteInit.java类的（frameworks\base\core\java\com\android\internal\os\ZygoteInit.java） main方法中通过forkSystemServer启动。
public static void main(String argv[]) {
....
//设置变量区分是否启动SystemServer
boolean startSystemServer = false;
String socketName = "zygote";
String abiList = null;
boolean enableLazyPreload = false;
for (int i = 1; i < argv.length; i++) {
if ("start-system-server".equals(argv[i])) {
// 需要启动时候，将标志位设置为true
startSystemServer = true;
} else if ("--enable-lazy-preload".equals(argv[i])) {
enableLazyPreload = true;
}
... ...
if (startSystemServer) {
// 通过 Zygote fork 出 SystemServer
Runnable r = forkSystemServer(abiList, socketName, zygoteServer);
// {@code r == null} in the parent (zygote) process, and {@code r != null} in the
// child (system_server) process.
if (r != null) {
r.run();
return;
}
}四、 SystemServer 启动入门 main 方法
main 入口 通过 new SystemServer().run();开启SystemServer启动。
main 入口代码如下：
/**
* The main entry point from zygote.
*/
public static void main(String[] args) {
new SystemServer().run();
}通过Main入口,调用SystemServer 构造方法。
public SystemServer() {
// 检查工程模式.
mFactoryTestMode = FactoryTest.getMode();
// 判断是否是重启
mRuntimeRestart = "1".equals(SystemProperties.get("sys.boot_completed"));
mRuntimeStartElapsedTime = SystemClock.elapsedRealtime();
mRuntimeStartUptime = SystemClock.uptimeMillis();
}
private void run() {
... ...
}五、SystemServer Run 方法初始与启动
SystemServer Run 方法 代码
private void run() {
try {
traceBeginAndSlog("InitBeforeStartServices");
//初始化时间
if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
Slog.w(TAG, "System clock is before 1970; setting to 1970.");
SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
}
//设置默认时区
String timezoneProperty = SystemProperties.get("persist.sys.timezone");
if (timezoneProperty == null || timezoneProperty.isEmpty()) {
Slog.w(TAG, "Timezone not set; setting to GMT.");
SystemProperties.set("persist.sys.timezone", "GMT");
}
... ...
// 开始进入Android SystemServer
Slog.i(TAG, "Entered the Android system server!");
int uptimeMillis = (int) SystemClock.elapsedRealtime();
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, uptimeMillis);
if (!mRuntimeRestart) {
MetricsLogger.histogram(null, "boot_system_server_init", uptimeMillis);
}
... ...
//如果支持指纹，需初始化指纹ro.build.fingerprint
Build.ensureFingerprintProperty();
... ...
// 初始化 native services.
System.loadLibrary("android_servers");
// 检查最近一次关机是否失败
performPendingShutdown();
// 初始化 the system context.
createSystemContext();
// 创建 system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);
mSystemServiceManager.setStartInfo(mRuntimeRestart,
mRuntimeStartElapsedTime, mRuntimeStartUptime);
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
// 初始化SystemServer 线程池
SystemServerInitThreadPool.get();
} finally {
traceEnd(); // InitBeforeStartServices
}
... ...
// 开始启动 services.
try {
traceBeginAndSlog("StartServices");
// 1. 启动引导服务 详见分析六
startBootstrapServices();
// 2. 启动核心服务 详见分析七
startCoreServices();
// 3.启动其他服务 详见分析八
startOtherServices();
SystemServerInitThreadPool.shutdown();
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
traceEnd();
}
StrictMode.initVmDefaults(null);
}
六、SystemServer 的引导服务有哪些
SystemServer启动的常用引导服务有installed 、DeviceIdentifiersPolicyService、 ActivityManagerService.、PowerManagerService 、 RecoverySystemService 、 LightsService 、 PackageManagerService、UserManagerService、OverlayManagerService等。
startBootstrapServices代码部分如下：
/**
* Starts the small tangle of critical services that are needed to get
* the system off the ground. These services have complex mutual dependencies
* which is why we initialize them all in one place here. Unless your service
* is also entwined in these dependencies, it should be initialized in one of
* the other functions.
*/
private void startBootstrapServices() {
Slog.i(TAG, "Reading configuration...");
final String TAG_SYSTEM_CONFIG = "ReadingSystemConfig";
traceBeginAndSlog(TAG_SYSTEM_CONFIG);
SystemServerInitThreadPool.get().submit(SystemConfig::getInstance, TAG_SYSTEM_CONFIG);
traceEnd();
// 启动 installed
traceBeginAndSlog("StartInstaller");
Installer installer = mSystemServiceManager.startService(Installer.class);
traceEnd();
//启动 设备标识符 服务
traceBeginAndSlog("DeviceIdentifiersPolicyService");
mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class);
traceEnd();
// 启动 AMS.
traceBeginAndSlog("StartActivityManager");
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
traceEnd();
//启动 PMS
traceBeginAndSlog("StartPowerManager");
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
traceEnd();
//初始化电源管理功能
traceBeginAndSlog("InitPowerManagement");
mActivityManagerService.initPowerManagement();
traceEnd();
// 启动 RecoverySystemService
traceBeginAndSlog("StartRecoverySystemService");
mSystemServiceManager.startService(RecoverySystemService.class);
traceEnd();
// 为启动事件添加记录
RescueParty.noteBoot(mSystemContext);
// 启动 LightsService 管理LEDs 和背光显示
traceBeginAndSlog("StartLightsService");
mSystemServiceManager.startService(LightsService.class);
traceEnd();
traceBeginAndSlog("StartSidekickService");
// Package manager isn't started yet; need to use SysProp not hardware feature
if (SystemProperties.getBoolean("config.enable_sidekick_graphics", false)) {
mSystemServiceManager.startService(WEAR_SIDEKICK_SERVICE_CLASS);
}
traceEnd();
// Display manager is needed to provide display metrics before package manager
// starts up.
traceBeginAndSlog("StartDisplayManager");
mDisplayManagerService = mSystemServiceManager.startService(LightsService.class);
traceEnd();
// We need the default display before we can initialize the package manager.
traceBeginAndSlog("WaitForDisplay");
mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
traceEnd();
// Only run "core" apps if we're encrypting the device.
String cryptState = SystemProperties.get("vold.decrypt");
if (ENCRYPTING_STATE.equals(cryptState)) {
Slog.w(TAG, "Detected encryption in progress - only parsing core apps");
mOnlyCore = true;
} else if (ENCRYPTED_STATE.equals(cryptState)) {
Slog.w(TAG, "Device encrypted - only parsing core apps");
mOnlyCore = true;
}
// 启动 PackageManagerService
if (!mRuntimeRestart) {
MetricsLogger.histogram(null, "boot_package_manager_init_start",
(int) SystemClock.elapsedRealtime());
}
traceBeginAndSlog("StartPackageManagerService");
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
mFirstBoot = mPackageManagerService.isFirstBoot();
mPackageManager = mSystemContext.getPackageManager();
traceEnd();
if (!mRuntimeRestart && !isFirstBootOrUpgrade()) {
MetricsLogger.histogram(null, "boot_package_manager_init_ready",
(int) SystemClock.elapsedRealtime());
}
// Manages A/B OTA dexopting. This is a bootstrap service as we need it to rename
// A/B artifacts after boot, before anything else might touch/need them.
// Note: this isn't needed during decryption (we don't have /data anyways).
if (!mOnlyCore) {
boolean disableOtaDexopt = SystemProperties.getBoolean("config.disable_otadexopt",
false);
if (!disableOtaDexopt) {
traceBeginAndSlog("StartOtaDexOptService");
try {
OtaDexoptService.main(mSystemContext, mPackageManagerService);
} catch (Throwable e) {
reportWtf("starting OtaDexOptService", e);
} finally {
traceEnd();
}
}
}
//启动多用户 UserManagerService
traceBeginAndSlog("StartUserManagerService");
mSystemServiceManager.startService(UserManagerService.LifeCycle.class);
traceEnd();
// 初始化属性缓存
traceBeginAndSlog("InitAttributerCache");
AttributeCache.init(mSystemContext);
traceEnd();
// Set up the Application instance for the system process and get started.
traceBeginAndSlog("SetSystemProcess");
mActivityManagerService.setSystemProcess();
traceEnd();
// DisplayManagerService needs to setup android.display scheduling related policies
// since setSystemProcess() would have overridden policies due to setProcessGroup
mDisplayManagerService.setupSchedulerPolicies();
/// M: CTA requirement - permission control @{
/*
* M: MOTA for CTA permissions handling
* This function is used for granting CTA permissions after OTA upgrade.
* This should be placed after AMS is added to ServiceManager and before
* starting other services since granting permissions needs AMS instance
* to do permission checking.
*/
mPackageManagerService.onAmsAddedtoServiceMgr();
/// @}
// 启动 OverlayManagerService
traceBeginAndSlog("StartOverlayManagerService");
mSystemServiceManager.startService(new OverlayManagerService(mSystemContext, installer));
traceEnd();
// The sensor service needs access to package manager service, app ops
// service, and permissions service, therefore we start it after them.
// Start sensor service in a separate thread. Completion should be checked
// before using it.
mSensorServiceStart = SystemServerInitThreadPool.get().submit(() -> {
TimingsTraceLog traceLog = new TimingsTraceLog(
SYSTEM_SERVER_TIMING_ASYNC_TAG, Trace.TRACE_TAG_SYSTEM_SERVER);
traceLog.traceBegin(START_SENSOR_SERVICE);
startSensorService();
traceLog.traceEnd();
}, START_SENSOR_SERVICE);
}
七、SystemServer 的核心服务有哪些
SystemServer 核心服务 有 BatteryService 、UsageStatsService、WebViewUpdateService、BinderCallsStatsService4种核心服务。
startCoreServices 代码部分如下：
/**
* Starts some essential services that are not tangled up in the bootstrap process.
*/
private void startCoreServices() {
// 启动 BatteryService 管理电池服务（电压、电量、温度）
traceBeginAndSlog("StartBatteryService");
// Tracks the battery level. Requires LightService.
mSystemServiceManager.startService(BatteryService.class);
traceEnd();
// 启动 UsageStatsService 收集应用持久化数据的服务
traceBeginAndSlog("StartUsageService");
mSystemServiceManager.startService(UsageStatsService.class);
mActivityManagerService.setUsageStatsManager(
LocalServices.getService(UsageStatsManagerInternal.class));
traceEnd();
// 启动 WebViewUpdateService 监视 WebView 是否更新
if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_WEBVIEW)) {
traceBeginAndSlog("StartWebViewUpdateService");
mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class);
traceEnd();
}
//启动 CPU Binder 调度服务
traceBeginAndSlog("StartBinderCallsStatsService");
BinderCallsStatsService.start();
traceEnd();
}
八、SystemServer 的其他服务有哪些
startOtherServices 启动的服务主要有： KeyChainSystemService、TelecomLoaderService、AccountManagerService、ContentService、DropBoxManagerService、VibratorService、AlarmManagerService、Watchdog、 InputManagerService、WindowManagerService、IpConnectivityMetrics、NetworkWatchlistService、PinnerService等服务。
startOtherServices代码部分如下：
/**
* Starts a miscellaneous grab bag of stuff that has yet to be refactored
* and organized.
*/
private void startOtherServices() {
... ...
traceBeginAndSlog("StartKeyAttestationApplicationIdProviderService");
ServiceManager.addService("sec_key_att_app_id_provider",
new KeyAttestationApplicationIdProviderService(context));
traceEnd();
// 启动 KeyChainSystemService
traceBeginAndSlog("StartKeyChainSystemService");
mSystemServiceManager.startService(KeyChainSystemService.class);
traceEnd();
traceBeginAndSlog("StartSchedulingPolicyService");
ServiceManager.addService("scheduling_policy", new SchedulingPolicyService());
traceEnd();
// 启动 TelecomLoaderService
traceBeginAndSlog("StartTelecomLoaderService");
mSystemServiceManager.startService(TelecomLoaderService.class);
traceEnd();
traceBeginAndSlog("StartTelephonyRegistry");
telephonyRegistry = new TelephonyRegistry(context);
ServiceManager.addService("telephony.registry", telephonyRegistry);
traceEnd();
traceBeginAndSlog("StartEntropyMixer");
mEntropyMixer = new EntropyMixer(context);
traceEnd();
mContentResolver = context.getContentResolver();
// 启动 用户管理服务 ，必现在StartContentService 之前
traceBeginAndSlog("StartAccountManagerService");
mSystemServiceManager.startService(ACCOUNT_SERVICE_CLASS);
traceEnd();
// 启动 ContentService
traceBeginAndSlog("StartContentService");
mSystemServiceManager.startService(CONTENT_SERVICE_CLASS);
traceEnd();
// 安装系统Provider 例如 SettingProvider CantacttProvider
traceBeginAndSlog("InstallSystemProviders");
mActivityManagerService.installSystemProviders();
// Now that SettingsProvider is ready, reactivate SQLiteCompatibilityWalFlags
SQLiteCompatibilityWalFlags.reset();
traceEnd();
// 启动 DropBoxManagerService
// 由于 依赖SettingsProvider，必须在InstallSystemProviders之后启动
traceBeginAndSlog("StartDropBoxManager");
mSystemServiceManager.startService(DropBoxManagerService.class);
traceEnd();
//启动 VibratorService 震动服务
traceBeginAndSlog("StartVibratorService");
vibrator = new VibratorService(context);
ServiceManager.addService("vibrator", vibrator);
traceEnd();
if (!isWatch) {
traceBeginAndSlog("StartConsumerIrService");
consumerIr = new ConsumerIrService(context);
ServiceManager.addService(Context.CONSUMER_IR_SERVICE, consumerIr);
traceEnd();
}
// 启动 AlarmManagerService
traceBeginAndSlog("StartAlarmManagerService");
if(!sMtkSystemServerIns.startMtkAlarmManagerService()){
mSystemServiceManager.startService(AlarmManagerService.class);
}
traceEnd();
// 初始化 看门狗
traceBeginAndSlog("InitWatchdog");
final Watchdog watchdog = Watchdog.getInstance();
watchdog.init(context, mActivityManagerService);
traceEnd();
//启动 InputManagerService
traceBeginAndSlog("StartInputManagerService");
inputManager = new InputManagerService(context);
traceEnd();
//启动 WindowManagerService
traceBeginAndSlog("StartWindowManagerService");
// WMS needs sensor service ready
ConcurrentUtils.waitForFutureNoInterrupt(mSensorServiceStart, START_SENSOR_SERVICE);
mSensorServiceStart = null;
wm = WindowManagerService.main(context, inputManager,
mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL,
!mFirstBoot, mOnlyCore, new PhoneWindowManager());
ServiceManager.addService(Context.WINDOW_SERVICE, wm, /* allowIsolated= */ false,
DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PROTO);
ServiceManager.addService(Context.INPUT_SERVICE, inputManager,
/* allowIsolated= */ false, DUMP_FLAG_PRIORITY_CRITICAL);
traceEnd();
traceBeginAndSlog("SetWindowManagerService");
mActivityManagerService.setWindowManager(wm);
traceEnd();
traceBeginAndSlog("WindowManagerServiceOnInitReady");
wm.onInitReady();
traceEnd();
// Start receiving calls from HIDL services. Start in in a separate thread
// because it need to connect to SensorManager. This have to start
// after START_SENSOR_SERVICE is done.
SystemServerInitThreadPool.get().submit(() -> {
TimingsTraceLog traceLog = new TimingsTraceLog(
SYSTEM_SERVER_TIMING_ASYNC_TAG, Trace.TRACE_TAG_SYSTEM_SERVER);
traceLog.traceBegin(START_HIDL_SERVICES);
startHidlServices();
traceLog.traceEnd();
}, START_HIDL_SERVICES);
if (!isWatch) {
traceBeginAndSlog("StartVrManagerService");
mSystemServiceManager.startService(VrManagerService.class);
traceEnd();
}
traceBeginAndSlog("StartInputManager");
inputManager.setWindowManagerCallbacks(wm.getInputMonitor());
inputManager.start();
traceEnd();
// TODO: Use service dependencies instead.
traceBeginAndSlog("DisplayManagerWindowManagerAndInputReady");
mDisplayManagerService.windowManagerAndInputReady();
traceEnd();
// Skip Bluetooth if we have an emulator kernel
// TODO: Use a more reliable check to see if this product should
// support Bluetooth - see bug 988521
if (isEmulator) {
Slog.i(TAG, "No Bluetooth Service (emulator)");
} else if (mFactoryTestMode == FactoryTest.FACTORY_TEST_LOW_LEVEL) {
Slog.i(TAG, "No Bluetooth Service (factory test)");
} else if (!context.getPackageManager().hasSystemFeature
(PackageManager.FEATURE_BLUETOOTH)) {
Slog.i(TAG, "No Bluetooth Service (Bluetooth Hardware Not Present)");
} else {
traceBeginAndSlog("StartBluetoothService");
mSystemServiceManager.startService(BluetoothService.class);
traceEnd();
}
// 启动 IpConnectivityMetrics
traceBeginAndSlog("IpConnectivityMetrics");
mSystemServiceManager.startService(IpConnectivityMetrics.class);
traceEnd();
// 启动 NetworkWatchlistService
traceBeginAndSlog("NetworkWatchlistService");
mSystemServiceManager.startService(NetworkWatchlistService.Lifecycle.class);
traceEnd();
// 启动 PinnerService
traceBeginAndSlog("PinnerService");
mSystemServiceManager.startService(PinnerService.class);
traceEnd();
} catch (RuntimeException e) {
至此，本篇已结束，如有不对的地方，欢迎您的建议与指正。同时期待您的关注，感谢您的阅读，谢谢！