Zygote是所有应用的鼻祖，SystemServer和其他所有Dalivik虚拟机进程都是由Zygote fork而来。Zygote fork的第一个进程就是SystemServer，其在手机中的进程名为system_server。
回顾ZygoteInit的startSystemServer
public static void main(String argv[]) {
ZygoteServer zygoteServer = null;
...
try {
zygoteServer = new ZygoteServer(isPrimaryZygote);
if (startSystemServer) {
//fork system_server
Runnable r = forkSystemServer(abiList, zygoteSocketName, zygoteServer);
// {@code r == null} in the parent (zygote) process, and {@code r != null} in the
// child (system_server) process.
if (r != null) {
r.run(); //启动SystemServer.java的main()
return; //Android 8.0之前是通过抛异常的方式来启动，这里是直接return出去，用来清空栈，提高栈帧利用率
}
}
caller = zygoteServer.runSelectLoop(abiList);
} catch (Throwable ex) {
Log.e(TAG, "System zygote died with exception", ex);
throw ex;
} finally {
if (zygoteServer != null) {
zygoteServer.closeServerSocket();
}
}
if (caller != null) {
caller.run();
}
}
ZygoteInit#forkSystemServer
private static Runnable forkSystemServer(String abiList, String socketName,
ZygoteServer zygoteServer) {
......
//参数准备，uid和gid都是为1000
String args[] = {
"--setuid=1000",
"--setgid=1000",
"--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,"
+ "1024,1032,1065,3001,3002,3003,3006,3007,3009,3010",
"--capabilities=" + capabilities + "," + capabilities,
"--nice-name=system_server",
"--runtime-args",
"--target-sdk-version=" + VMRuntime.SDK_VERSION_CUR_DEVELOPMENT,
"com.android.server.SystemServer",
};
ZygoteArguments parsedArgs = null;
int pid;
try {
//将上面准备的参数，按照ZygoteArguments的风格进行封装
parsedArgs = new ZygoteArguments(args);
Zygote.applyDebuggerSystemProperty(parsedArgs);
Zygote.applyInvokeWithSystemProperty(parsedArgs);
//通过fork"分裂"出子进程system_server
/* Request to fork the system server process */
pid = Zygote.forkSystemServer(
parsedArgs.mUid, parsedArgs.mGid,
parsedArgs.mGids,
parsedArgs.mRuntimeFlags,
null,
parsedArgs.mPermittedCapabilities,
parsedArgs.mEffectiveCapabilities);
} catch (IllegalArgumentException ex) {
throw new RuntimeException(ex);
}
//进入子进程system_server
if (pid == 0) {
// 处理32_64和64_32的情况
if (hasSecondZygote(abiList)) {
waitForSecondaryZygote(socketName); //需要等待第二个Zygote创建完成
}
// fork时会copy socket，Zygote原有的socket需要关闭
zygoteServer.closeServerSocket();
// system server进程处理自己的工作
return handleSystemServerProcess(parsedArgs);
}
return null;
}
ZygoteInit#handleSystemServerProcess
private static Runnable handleSystemServerProcess(ZygoteArguments parsedArgs) {
if (parsedArgs.mNiceName != null) {
Process.setArgV0(parsedArgs.mNiceName); //设置当前进程名为"system_server"
}
final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
if (systemServerClasspath != null) {
//执行dex优化操作
if (performSystemServerDexOpt(systemServerClasspath)) {
sCachedSystemServerClassLoader = null;
}
...
}
if (parsedArgs.mInvokeWith != null) {
String[] args = parsedArgs.mRemainingArgs;
//如果我们有一个非空系统服务器类路径，我们将不得不复制现有的参数并将类路径附加到它。
//当我们执行一个新进程时，ART将正确地处理类路径。
if (systemServerClasspath != null) {
String[] amendedArgs = new String[args.length + 2];
amendedArgs[0] = "-cp";
amendedArgs[1] = systemServerClasspath;
System.arraycopy(args, 0, amendedArgs, 2, args.length);
args = amendedArgs;
}
//启动应用进程
WrapperInit.execApplication(parsedArgs.mInvokeWith,
parsedArgs.mNiceName, parsedArgs.mTargetSdkVersion,
VMRuntime.getCurrentInstructionSet(), null, args);
throw new IllegalStateException("Unexpected return from WrapperInit.execApplication");
} else {
// 创建类加载器，并赋予当前线程
createSystemServerClassLoader();
ClassLoader cl = sCachedSystemServerClassLoader;
if (cl != null) {
Thread.currentThread().setContextClassLoader(cl);
}
//system_server进入此分支
return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion,
parsedArgs.mRemainingArgs, cl);
}
}
ZygoteInit.java#zygoteInit
public static final Runnable zygoteInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
if (RuntimeInit.DEBUG) {
Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");
}
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
RuntimeInit.redirectLogStreams(); //重定向log输出
RuntimeInit.commonInit();//通用的一些初始化
ZygoteInit.nativeZygoteInit();//zygote初始化
//应用初始化
return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
}
RuntimeInit.java#commonInit
配置log，时区，http userAgent等基础信息
protected static final void commonInit() {
LoggingHandler loggingHandler = new LoggingHandler();
// 设置默认的未捕捉异常处理方法
RuntimeHooks.setUncaughtExceptionPreHandler(loggingHandler);
Thread.setDefaultUncaughtExceptionHandler(new KillApplicationHandler(loggingHandler));
// 设置时区，通过属性读出中国时区为"Asia/Shanghai"
RuntimeHooks.setTimeZoneIdSupplier(() -> SystemProperties.get("persist.sys.timezone"));
//重置log配置
LogManager.getLogManager().reset();
new AndroidConfig();
//设置默认的HTTP User-agent格式,用于 HttpURLConnection
String userAgent = getDefaultUserAgent();
System.setProperty("http.agent", userAgent);
/*
* Wire socket tagging to traffic stats.
*/
//设置socket的tag，用于网络流量统计
NetworkManagementSocketTagger.install();
...
}
RuntimeInit.java#applicaitonInit
protected static Runnable applicationInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
// If the application calls System.exit(), terminate the process
// immediately without running any shutdown hooks. It is not possible to
// shutdown an Android application gracefully. Among other things, the
// Android runtime shutdown hooks close the Binder driver, which can cause
// leftover running threads to crash before the process actually exits.
//true代表应用程序退出时不调用AppRuntime.onExit(),否则会在退出前调用
nativeSetExitWithoutCleanup(true);
// We want to be fairly aggressive about heap utilization, to avoid
// holding on to a lot of memory that isn't needed.
//设置虚拟机的内存利用率参数值为0.75
VMRuntime.getRuntime().setTargetHeapUtilization(0.75f);
VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);
//解析参数
final Arguments args = new Arguments(argv);
// The end of of the RuntimeInit event (see #zygoteInit).
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
// Remaining arguments are passed to the start class's static main
//找到systemServer 的main方法
return findStaticMain(args.startClass, args.startArgs, classLoader);
}
RuntimeInit.java#findStaticMain()
protected static Runnable findStaticMain(String className, String[] argv,
ClassLoader classLoader) {
Class<?> cl;
try {
//拿到com.android.server.SystemServer 的类对象
cl = Class.forName(className, true, classLoader);
} catch (ClassNotFoundException ex) {
throw new RuntimeException(
"Missing class when invoking static main " + className,
ex);
}
Method m;
try {
//得到SystemServer的main()方法
m = cl.getMethod("main", new Class[] { String[].class });
} catch (NoSuchMethodException ex) {
throw new RuntimeException(
"Missing static main on " + className, ex);
} catch (SecurityException ex) {
throw new RuntimeException(
"Problem getting static main on " + className, ex);
}
int modifiers = m.getModifiers();
if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
throw new RuntimeException(
"Main method is not public and static on " + className);
}
/*
* This throw gets caught in ZygoteInit.main(), which responds
* by invoking the exception's run() method. This arrangement
* clears up all the stack frames that were required in setting
* up the process.
*/
//把MethodAndArgsCaller的对象返回给ZygoteInit.main()
//这样做的好处是能清空栈，提高栈帧利用率。清除了设置进程所需的多有堆栈帧
return new MethodAndArgsCaller(m, argv);
}
static class MethodAndArgsCaller implements Runnable {
/** method to call */
private final Method mMethod;
/** argument array */
private final String[] mArgs;
public MethodAndArgsCaller(Method method, String[] args) {
mMethod = method;
mArgs = args;
}
public void run() {
try {
//根据传递进来的参数，可知此处通过反射机制调用的是
SystemServer.main()方法
mMethod.invoke(null, new Object[] { mArgs });
} catch (IllegalAccessException ex) {
throw new RuntimeException(ex);
} catch (InvocationTargetException ex) {
Throwable cause = ex.getCause();
if (cause instanceof RuntimeException) {
throw (RuntimeException) cause;
} else if (cause instanceof Error) {
throw (Error) cause;
}
throw new RuntimeException(ex);
}
}
}
SystemServer.java#main
main函数由Zygote进程fork后运行，作用是new 一个SystemServer对象，在调用该对象的run()方法
/* The main entry point from zygote.
*/
public static void main(String[] args) {
new SystemServer().run();
}
SystemServer.java#run
先初始化一些系统变量，加载类库，启动引导服务，核心服务，和其他服务。
private void run() {
try {
traceBeginAndSlog("InitBeforeStartServices");
// Record the process start information in sys props.
//从属性中读取system_server进程的一些信息
SystemProperties.set(SYSPROP_START_COUNT, String.valueOf(mStartCount));
SystemProperties.set(SYSPROP_START_ELAPSED, String.valueOf(mRuntimeStartElapsedTime));
SystemProperties.set(SYSPROP_START_UPTIME, String.valueOf(mRuntimeStartUptime));
EventLog.writeEvent(EventLogTags.SYSTEM_SERVER_START,
mStartCount, mRuntimeStartUptime, mRuntimeStartElapsedTime);
//如果一个设备的时钟是在1970年之前(0年之前)，
//那么很多api 都会因为处理负数而崩溃，尤其是java.io.File#setLastModified
//我把把时间设置为1970
if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
Slog.w(TAG, "System clock is before 1970; setting to 1970.");
SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
}
//如果时区不存在，设置时区为GMT
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");
}
//变更虚拟机的库文件，对于Android 10.0默认采用的是libart.so
SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());
// Mmmmmm... more memory!
//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();
...
//系统服务器必须一直运行，所以它需要尽可能高效地使用内存
//设置内存的可能有效使用率为0.8
VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
//一些设备依赖于运行时指纹生成，所以在进一步启动之前，请确保我们已经定义了它。
Build.ensureFingerprintProperty();
//访问环境变量前，需要明确地指定用户
//在system_server中，任何传入的包都应该被解除，以避免抛出BadParcelableException。
BaseBundle.setShouldDefuse(true);
//在system_server中，当打包异常时，信息需要包含堆栈跟踪
Parcel.setStackTraceParceling(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);
//设置system_server中binder线程的最大数量,最大值为31
BinderInternal.setMaxThreads(sMaxBinderThreads);
//准备主线程lopper，即在当前线程运行
android.os.Process.setThreadPriority(
android.os.Process.THREAD_PRIORITY_FOREGROUND);
android.os.Process.setCanSelfBackground(false);
Looper.prepareMainLooper();
Looper.getMainLooper().setSlowLogThresholdMs(
SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS);
//加载android_servers.so库，初始化native service
System.loadLibrary("android_servers");
// Debug builds - allow heap profiling.
//如果是Debug版本，允许堆内存分析
if (Build.IS_DEBUGGABLE) {
initZygoteChildHeapProfiling();
}
//检测上次关机过程是否失败，这个调用可能不会返回
performPendingShutdown();
//初始化系统上下文
createSystemContext();
//创建系统服务管理--SystemServiceManager
mSystemServiceManager = new SystemServiceManager(mSystemContext);
mSystemServiceManager.setStartInfo(mRuntimeRestart,
mRuntimeStartElapsedTime, mRuntimeStartUptime);
//将mSystemServiceManager添加到本地服务的成员sLocalServiceObjects
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
// Prepare the thread pool for init tasks that can be parallelized
//为可以并行化的init任务准备线程池
SystemServerInitThreadPool.get();
} finally {
traceEnd(); // InitBeforeStartServices
}
// Start services.
//启动服务
try {
traceBeginAndSlog("StartServices");
startBootstrapServices(); // 启动引导服务
startCoreServices(); // 启动核心服务
startOtherServices(); // 启动其他服务
SystemServerInitThreadPool.shutdown(); //停止线程池
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
traceEnd();
}
//为当前的虚拟机初始化VmPolicy
StrictMode.initVmDefaults(null);
...
// Loop forever.
//死循环执行
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
SystemServer.java#createSystemContext
初始化系统上下文，该过程会创建对象有ActivityThread,Instrumentation,ContextImpl,LoadedAPk,Applicaiton
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(DEFAULT_SYSTEM_THEME);
//获取systemui上下文信息，并设置主题
final Context systemUiContext = activityThread.getSystemUiContext();
systemUiContext.setTheme(DEFAULT_SYSTEM_THEME);
}
SystemServer.java#startBootstrapServices
用来启动系统Boot级服务，有ActivityManager,PowerManagerService,LightsService,DisplayManagerService,PackageManagerService等
private void startBootstrapServices() {
traceBeginAndSlog("StartWatchdog");
//启动watchdog
//尽早启动watchdog，如果在早起启动时发生死锁，我们可以让system_server
//崩溃，从而进行详细分析
final Watchdog watchdog = Watchdog.getInstance();
watchdog.start();
traceEnd();
...
//添加PLATFORM_COMPAT_SERVICE，Platform compat服务被ActivityManagerService、PackageManagerService
//以及将来可能出现的其他服务使用。
traceBeginAndSlog("PlatformCompat");
ServiceManager.addService(Context.PLATFORM_COMPAT_SERVICE,
new PlatformCompat(mSystemContext));
traceEnd();
//阻塞等待installd完成启动，以便有机会创建具有适当权限的关键目录，如/data/user。
//我们需要在初始化其他服务之前完成此任务。
traceBeginAndSlog("StartInstaller");
Installer installer = mSystemServiceManager.startService(Installer.class);
traceEnd();
...
//启动服务ActivityManagerService,并为其设置mSystemServiceManager和installer
traceBeginAndSlog("StartActivityManager");
ActivityTaskManagerService atm = mSystemServiceManager.startService(
ActivityTaskManagerService.Lifecycle.class).getService();
mActivityManagerService = ActivityManagerService.Lifecycle.startService(mSystemServiceManager, atm);
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
mWindowManagerGlobalLock = atm.getGlobalLock();
traceEnd();
//启动服务PowerManagerService
//Power manager需要尽早启动，因为其他服务需要它。
//本机守护进程可能正在监视它的注册，
//因此它必须准备好立即处理传入的绑定器调用(包括能够验证这些调用的权限)
。
traceBeginAndSlog("StartPowerManager");
mPowerManagerService = mSystemServiceManager.startService(
PowerManagerService.class);
traceEnd();
...
//初始化power management
traceBeginAndSlog("InitPowerManagement");
mActivityManagerService.initPowerManagement();
traceEnd();
//启动recovery system，以防需要重新启动
traceBeginAndSlog("StartRecoverySystemService");
mSystemServiceManager.startService(RecoverySystemService.class);
traceEnd();
...
//启动服务LightsService
//管理led和显示背光，所以我们需要它来打开显示
traceBeginAndSlog("StartLightsService");
mSystemServiceManager.startService(LightsService.class);
traceEnd();
...
//启动服务DisplayManagerService
//显示管理器需要在包管理器之前提供显示指标
traceBeginAndSlog("StartDisplayManager");
mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);
traceEnd();
// Boot Phases: Phase100: 在初始化package manager之前，需要默认的显示.
traceBeginAndSlog("WaitForDisplay");
mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
traceEnd();
//当设备正在加密时，仅运行核心
String cryptState = VoldProperties.decrypt().orElse("");
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;
}
...
//启动服务PackageManagerService
traceBeginAndSlog("StartPackageManagerService");
try {
Watchdog.getInstance().pauseWatchingCurrentThread("packagemanagermain");
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
} finally {
Watchdog.getInstance().resumeWatchingCurrentThread("packagemanagermain");
}
...
//启动服务UserManagerService，新建目录/data/user/
traceBeginAndSlog("StartUserManagerService");
mSystemServiceManager.startService(UserManagerService.LifeCycle.class);
traceEnd();
// Set up the Application instance for the system process and get started.
//为系统进程设置应用程序实例并开始。
//设置AMS
traceBeginAndSlog("SetSystemProcess");
mActivityManagerService.setSystemProcess();
traceEnd();
//使用一个ActivityManager实例完成watchdog设置并监听重启，
//只有在ActivityManagerService作为一个系统进程正确启动后才能这样做
traceBeginAndSlog("InitWatchdog");
watchdog.init(mSystemContext, mActivityManagerService);
traceEnd();
//传感器服务需要访问包管理器服务、app ops服务和权限服务，
//因此我们在它们之后启动它。
//在单独的线程中启动传感器服务。在使用它之前应该检查完成情况。
mSensorServiceStart = SystemServerInitThreadPool.get().submit(() -> {
TimingsTraceLog traceLog = new TimingsTraceLog(
SYSTEM_SERVER_TIMING_ASYNC_TAG, Trace.
TRACE_TAG_SYSTEM_SERVER);
traceLog.traceBegin(START_SENSOR_SERVICE);
startSensorService(); //启动传感器服务
traceLog.traceEnd();
}, START_SENSOR_SERVICE);
}
SystemServerManager.java$statService()
/**
* Creates and starts a system service. The class must be a subclass of
* {@link com.android.server.SystemService}.
*
* @param serviceClass A Java class that implements the SystemService interface.
* @return The service instance, never null.
* @throws RuntimeException if the service fails to start.
*/
@SuppressWarnings("unchecked")
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);
// 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); //1
} 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);
}
startService(service);
return service;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
}
}
public void startService(@NonNull final SystemService service) {
// Register it.
mServices.add(service); //2
// Start it.
long time = SystemClock.elapsedRealtime();
try {
service.onStart(); //3
} catch (RuntimeException ex) {
throw new RuntimeException("Failed to start service " + service.getClass().getName()
+ ": onStart threw an exception", ex);
}
warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart");
}
通过反射创建SystemService，然后将服务添加到mServices中，这里mServices是一个存储SystemService类型的ArrayList。然后调用服务的onStart函数启动并返回。
我们看看PackageManagerService，它是通过另外一种方式启动的，直接调用了PackageManagerService的main函数:
public static PackageManagerService main(Context context, Installer installer,
boolean factoryTest, boolean onlyCore) {
// Self-check for initial settings.
PackageManagerServiceCompilerMapping.checkProperties();
PackageManagerService m = new PackageManagerService(context, installer,
factoryTest, onlyCore);
m.enableSystemUserPackages();
ServiceManager.addService("package", m);
final PackageManagerNative pmn = m.new PackageManagerNative();
ServiceManager.addService("package_native", pmn);
return m;
}
创建PackageMangerService实例，然后注册到ServiceManager中。ServiceManager用来管理系统中的各种Service，用系统C/S架构中的Binder机制通信，Client端要使用某个Service，则需要先到ServiceManager查询Service的相关信息，然后根据Service的相关信息与Service所在的进程建立通讯通路，这样Client端就可以使用Service了。
SystemServer.java#startCoreServices
启动核心服务BatteryService,WebViewUpdateService等
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));
//启动服务WebViewUpdateService
//跟踪可更新的WebView是否处于就绪状态，并监视更新安装
if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_WEBVIEW)) {
mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class);
}
//启动CachedDeviceStateService，跟踪和缓存设备状态
mSystemServiceManager.startService(CachedDeviceStateService.class);
//启动BinderCallsStatsService, 跟踪在绑定器调用中花费的cpu时间
traceBeginAndSlog("StartBinderCallsStatsService");
mSystemServiceManager.startService(BinderCallsStatsService.LifeCycle.class);
traceEnd();
//启动LooperStatsService，跟踪处理程序中处理消息所花费的时间。
traceBeginAndSlog("StartLooperStatsService");
mSystemServiceManager.startService(LooperStatsService.Lifecycle.class);
traceEnd();
//启动RollbackManagerService，管理apk回滚
mSystemServiceManager.startService(RollbackManagerService.class);
//启动BugreportManagerService，捕获bugreports的服务
mSystemServiceManager.startService(BugreportManagerService.class);
//启动GpuService，为GPU和GPU驱动程序提供服务。
mSystemServiceManager.startService(GpuService.class);
}
SystemServer.java#startOtherServices
这里面启动的服务太多，大体流程如下
private void startOtherServices() {
...
//启动TelecomLoaderService，通话相关核心服务
mSystemServiceManager.startService(TelecomLoaderService.class);
//启动TelephonyRegistry
telephonyRegistry = new TelephonyRegistry(context);
ServiceManager.addService("telephony.registry", telephonyRegistry);
...
//启动AlarmManagerService，时钟管理
mSystemServiceManager.startService(new AlarmManagerService(context));
...
//启动InputManagerService
inputManager = new InputManagerService(context);
ServiceManager.addService(Context.INPUT_SERVICE, inputManager,
/* allowIsolated= */ false, DUMP_FLAG_PRIORITY_CRITICAL);
...
inputManager.setWindowManagerCallbacks(wm.getInputManagerCallback());
inputManager.start();
...
//Phase480:在接收到此启动阶段后，服务可以获得锁设置数据
mSystemServiceManager.startBootPhase(SystemService.PHASE_LOCK_SETTINGS_READY);
//Phase500:在接收到这个启动阶段之后，服务可以安全地调用核心系统服务，
//如PowerManager或PackageManager。
mSystemServiceManager.startBootPhase(SystemService.PHASE_SYSTEM_SERVICES_READY);
mActivityManagerService.systemReady(() -> {
//Phase550:在接收到此引导阶段后，服务可以广播意图。
mSystemServiceManager.startBootPhase(
SystemService.PHASE_ACTIVITY_MANAGER_READY);
//Phase600:在接收到这个启动阶段后，服务可以启动/绑定到第三方应用程序。
//此时，应用程序将能够对服务进行绑定调用。
mSystemServiceManager.startBootPhase(
SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);
}
}
总结
- Zygote启动后fork的第一个进程为SystemServer,在手机中的进程别名为"system_server"，主要用来启动系统中的服务
- Zygote fork后，进入SystemServer的main()
- SystemServer在启动过程中，先初始化一些系统变量，加载类库，创建Context对象，创建SystemServiceManager对象等候再启动服务
- 启动的服务分为 引导服务(Boot Service)、核心服务(Core Service)和其他服务(Other Service)三大类，共90多个服务
- SystemServer在启动服务前，会尝试与Zygote建立Socket通信，通信成功后才去启动服务
- 启动的服务都单独运行在SystemServer的各自线程中，同属于SystemServer进程
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