public static void main(String argv[]) {...if (startSystemServer) {startSystemServer(abiList, socketName, zygoteServer);}...}

  /*** Prepare the arguments and fork for the system server process.*/private static boolean startSystemServer(String abiList, String socketName, ZygoteServer zygoteServer)throws Zygote.MethodAndArgsCaller, RuntimeException {.../* Hardcoded command line to start the system server */String args[] = {"--setuid=1000","--setgid=1000","--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1032,3001,3002,3003,3006,3007,3009,3010","--capabilities=" + capabilities + "," + capabilities,"--nice-name=system_server","--runtime-args","com.android.server.SystemServer",};ZygoteConnection.Arguments parsedArgs = null;int pid;try {parsedArgs = new ZygoteConnection.Arguments(args);ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);//Zygote fork SystemServer进程pid = Zygote.forkSystemServer(parsedArgs.uid, parsedArgs.gid,parsedArgs.gids,parsedArgs.debugFlags,null,parsedArgs.permittedCapabilities,parsedArgs.effectiveCapabilities);} catch (IllegalArgumentException ex) {throw new RuntimeException(ex);}/* For child process *///fork出来的进程pid == 0表示当前是在SystemServer进程中运行if (pid == 0) {if (hasSecondZygote(abiList)) {waitForSecondaryZygote(socketName);}//SystemServer进程不需要Socket，关闭Socket，此Socket是Zygote等待接受AMS创建进程请求的zygoteServer.closeServerSocket();handleSystemServerProcess(parsedArgs);}return true;}

/*** Finish remaining work for the newly forked system server process.*/private static void handleSystemServerProcess(ZygoteConnection.Arguments parsedArgs)throws Zygote.MethodAndArgsCaller {...if (parsedArgs.invokeWith != null) {...} else {ClassLoader cl = null;if (systemServerClasspath != null) {cl = createPathClassLoader(systemServerClasspath, parsedArgs.targetSdkVersion);Thread.currentThread().setContextClassLoader(cl);}/** Pass the remaining arguments to SystemServer.*/ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);}/* should never reach here */}

public static final void zygoteInit(int targetSdkVersion, String[] argv,ClassLoader classLoader) throws Zygote.MethodAndArgsCaller {if (RuntimeInit.DEBUG) {Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");}Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");RuntimeInit.redirectLogStreams();RuntimeInit.commonInit();//启动binder线程池ZygoteInit.nativeZygoteInit();//调用SystemServer中的main方法RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);}

 /* Hardcoded command line to start the system server */String args[] = {"--setuid=1000","--setgid=1000","--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1032,3001,3002,3003,3006,3007,3009,3010","--capabilities=" + capabilities + "," + capabilities,"--nice-name=system_server","--runtime-args","com.android.server.SystemServer",//这就是SystemServer全类名};

/*** The main entry point from zygote.*/public static void main(String[] args) {new SystemServer().run();}

private void run() {try {     ...//创建SystemServer进程中的LooperLooper.prepareMainLooper();// Initialize native services.System.loadLibrary("android_servers");// Check whether we failed to shut down last time we tried.// This call may not return.performPendingShutdown();// Initialize the system context.createSystemContext();// Create the system service manager.mSystemServiceManager = new SystemServiceManager(mSystemContext);mSystemServiceManager.setRuntimeRestarted(mRuntimeRestart);LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);// Prepare the thread pool for init tasks that can be parallelizedSystemServerInitThreadPool.get();} finally {traceEnd();  // InitBeforeStartServices}// Start services.try {traceBeginAndSlog("StartServices");//启动引导服务startBootstrapServices();//启动核心服务startCoreServices();//启动其他服务startOtherServices();SystemServerInitThreadPool.shutdown();} catch (Throwable ex) {Slog.e("System", "******************************************");Slog.e("System", "************ Failure starting system services", ex);throw ex;} finally {traceEnd();}// For debug builds, log event loop stalls to dropbox for analysis.if (StrictMode.conditionallyEnableDebugLogging()) {Slog.i(TAG, "Enabled StrictMode for system server main thread.");}if (!mRuntimeRestart && !isFirstBootOrUpgrade()) {int uptimeMillis = (int) SystemClock.elapsedRealtime();MetricsLogger.histogram(null, "boot_system_server_ready", uptimeMillis);final int MAX_UPTIME_MILLIS = 60 * 1000;if (uptimeMillis > MAX_UPTIME_MILLIS) {Slog.wtf(SYSTEM_SERVER_TIMING_TAG,"SystemServer init took too long. uptimeMillis=" + uptimeMillis);}}// Loop forever.Looper.loop();throw new RuntimeException("Main thread loop unexpectedly exited");}