---

知识回顾

启动第一个流程init

1，挂载文件系统，创建文件目录 调用selinux_setup权限安全相关
2，初始化内存空间 初始化属性服务 创建Epoll 注册监听子进程重启异常操作等，对子进程进行线程守护
3，startPropertyServic 开启属性服务 进行监听
4，LoadBootScripts 加载init.rc文件 进行解析 调用do_class_start 文件开启service
5，Service::Start函数->fork子进程->并且执行app_process文件，开启了zygote

Zygote的流程

1，startVm函数注册jvm startReg函数注册jni环境唤起 Zygote.main
2,forkSystemServer
3,preload预加载class 系统资源
4，调用runSelectLoop函数循环等待客户端连接
5，有客户端的连接后调用processOneCommand()函数 fork进程，初始化进程，创建ProcessState初始化binder
6，根据请求的targetClass 执行Main函数

前言

Android系统在启动的时候有两个非常重要的进程，Zygote & system_server。SystemServer是系统用来启动service的入口，比如我们常用的 AMS，WMS，PMS等都是由它创建的。
SystemServer主要是创建SystemServiceManager，对系统服务进行创建、启动以及管理。

---

源码分析

1.system_server

Zygote启动之后会调用ZygoteInit.java的main函数，会执行forkSystemServer

 private static Runnable forkSystemServer(String abiList, String socketName,
            ZygoteServer zygoteServer) {
       
       ……………………

        /* Hardcoded command line to start the system server */
        //准备 开启system_server的参数
        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 {
            //把参数包装成ZygoteArguments
            parsedArgs = new ZygoteArguments(args);
            Zygote.applyDebuggerSystemProperty(parsedArgs);
            Zygote.applyInvokeWithSystemProperty(parsedArgs);

            boolean profileSystemServer = SystemProperties.getBoolean(
                    "dalvik.vm.profilesystemserver", false);
            if (profileSystemServer) {
                parsedArgs.mRuntimeFlags |= Zygote.PROFILE_SYSTEM_SERVER;
            }

            /* Request to fork the system server process */
//            fork出来system_server 还是调用到native层com_android_internal_os_Zygote_nativeForkSystemServer
            pid = Zygote.forkSystemServer(
                    parsedArgs.mUid, parsedArgs.mGid,
                    parsedArgs.mGids,
                    parsedArgs.mRuntimeFlags,
                    null,
                    parsedArgs.mPermittedCapabilities,
                    parsedArgs.mEffectiveCapabilities);
        } catch (IllegalArgumentException ex) {
            throw new RuntimeException(ex);
        }

        /* For child process */
        if (pid == 0) {
            if (hasSecondZygote(abiList)) {
                waitForSecondaryZygote(socketName);
            }
            //关闭掉ServerSocket
            zygoteServer.closeServerSocket();
//这里我们看到返回的是一个Runnable 就可以联想到Zygote中的MethodAndArgsCaller
            return handleSystemServerProcess(parsedArgs);
        }

        return null;
    }
//fork最终会调用到Native层
//com_android_internal_os_Zygote_nativeForkSystemServer
//。文件目录/frameworks/base/core/jni/com_android_internal_os_Zygote.cpp。

static jint com_android_internal_os_Zygote_nativeForkSystemServer(
        JNIEnv* env, jclass, uid_t uid, gid_t gid, jintArray gids,
        jint runtime_flags, jobjectArray rlimits, jlong permitted_capabilities,
        jlong effective_capabilities) {
  std::vector<int> fds_to_close(MakeUsapPipeReadFDVector()),
                   fds_to_ignore(fds_to_close);

  fds_to_close.push_back(gUsapPoolSocketFD);

  if (gUsapPoolEventFD != -1) {
    fds_to_close.push_back(gUsapPoolEventFD);
    fds_to_ignore.push_back(gUsapPoolEventFD);
  }
  //调用forkCommon函数，这个之前在Zygote中有跟踪过，这里就不跟了。调用fork并返回pid_t
  pid_t pid = ForkCommon(env, true,
                         fds_to_close,
                         fds_to_ignore);
  if (pid == 0) {
      SpecializeCommon(env, uid, gid, gids, runtime_flags, rlimits,
                       permitted_capabilities, effective_capabilities,
                       MOUNT_EXTERNAL_DEFAULT, nullptr, nullptr, true,
                       false, nullptr, nullptr);
  } else if (pid > 0) {
      ALOGI("System server process %d has been created", pid);
      gSystemServerPid = pid;
      int status;
      if (waitpid(pid, &status, WNOHANG) == pid) {//做一次安全检查
          ALOGE("System server process %d has died. Restarting Zygote!", pid);
          RuntimeAbort(env, __LINE__, "System server process has died. Restarting Zygote!");
      }

      if (UsePerAppMemcg()) {
          if (!SetTaskProfiles(pid, std::vector<std::string>{"SystemMemoryProcess"})) {
              ALOGE("couldn't add process %d into system memcg group", pid);
          }
      }
  }
  return pid;
}

private static Runnable handleSystemServerProcess(ZygoteArguments parsedArgs) {
    Os.umask(S_IRWXG | S_IRWXO);

    if (parsedArgs.mNiceName != null) {
        Process.setArgV0(parsedArgs.mNiceName);
    }

    final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
    if (systemServerClasspath != null) {
        if (performSystemServerDexOpt(systemServerClasspath)) {
            sCachedSystemServerClassLoader = null;
        }
        boolean profileSystemServer = SystemProperties.getBoolean(
                "dalvik.vm.profilesystemserver", false);
        if (profileSystemServer && (Build.IS_USERDEBUG || Build.IS_ENG)) {
            try {
                prepareSystemServerProfile(systemServerClasspath);
            } catch (Exception e) {
                Log.wtf(TAG, "Failed to set up system server profile", e);
            }
        }
    }

    if (parsedArgs.mInvokeWith != null) {//这里是Null
        String[] args = parsedArgs.mRemainingArgs;
        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;
        }

        WrapperInit.execApplication(parsedArgs.mInvokeWith,
                parsedArgs.mNiceName, parsedArgs.mTargetSdkVersion,
                VMRuntime.getCurrentInstructionSet(), null, args);

        throw new IllegalStateException("Unexpected return from WrapperInit.execApplication");
    } else {
        createSystemServerClassLoader();//创建SystemServer的ClassLoader
        ClassLoader cl = sCachedSystemServerClassLoader;//将创建好的ClassLoader赋值给cl
        if (cl != null) {
            Thread.currentThread().setContextClassLoader(cl);
        }
        //调用ZygoteInit.zygoteInit 和Zygote一样 创建ProcessState 打开binder 并调用RuntimeInit.applicationInit 返回startClass的Main函数的caller也 也就是执行com.android.server.SystemServer的main函数
        return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion,
                parsedArgs.mRemainingArgs, cl);
    }

}

2.SystemServer.main

main函数转头就掉了run函数，run函数中 创建了Looper、加载了android_server函数库、创建了SystemServiceManager(对服务进行创建、启动和管理)并且添加到LocalService（一个ArrayMap）中、startBootstrapServices(开启引导服务)、startCoreServices(开启核心服务)、startOtherServices(开启其他服务)、Looper开启。

public static void main(String[] args) {
    //转头就钓了run函数
    new SystemServer().run();
}



private void run() {
    try {
        traceBeginAndSlog("InitBeforeStartServices");

        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);

        if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
            Slog.w(TAG, "System clock is before 1970; setting to 1970.");
            SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
        }

        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");
        }

        if (!SystemProperties.get("persist.sys.language").isEmpty()) {
            final String languageTag = Locale.getDefault().toLanguageTag();

            SystemProperties.set("persist.sys.locale", languageTag);
            SystemProperties.set("persist.sys.language", "");
            SystemProperties.set("persist.sys.country", "");
            SystemProperties.set("persist.sys.localevar", "");
        }

        Binder.setWarnOnBlocking(true);
        PackageItemInfo.forceSafeLabels();

        SQLiteGlobal.sDefaultSyncMode = SQLiteGlobal.SYNC_MODE_FULL;

        SQLiteCompatibilityWalFlags.init(null);

        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);
        }

        SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());

        VMRuntime.getRuntime().clearGrowthLimit();
        VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
        Build.ensureFingerprintProperty();
        Environment.setUserRequired(true);
        BaseBundle.setShouldDefuse(true);
        Parcel.setStackTraceParceling(true);
        BinderInternal.disableBackgroundScheduling(true);
        BinderInternal.setMaxThreads(sMaxBinderThreads);
        android.os.Process.setThreadPriority(
                android.os.Process.THREAD_PRIORITY_FOREGROUND);
        android.os.Process.setCanSelfBackground(false);
        Looper.prepareMainLooper();//创建消息的Looper
        Looper.getMainLooper().setSlowLogThresholdMs(
                SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS);
        //加载函数库 libandroid_servers.so
        System.loadLibrary("android_servers");

        if (Build.IS_DEBUGGABLE) {
            initZygoteChildHeapProfiling();
        }

        performPendingShutdown();

        // Initialize the system context.
        createSystemContext();//创建系统Context

        // Create the system service manager. 创建ServiceManager
        mSystemServiceManager = new SystemServiceManager(mSystemContext);
        mSystemServiceManager.setStartInfo(mRuntimeRestart,
                mRuntimeStartElapsedTime, mRuntimeStartUptime);
        //将SystemServiceManager添加到LocalServices中 LocalService 内部其实就是一个ArrayMap
        LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
        // Prepare the thread pool for init tasks that can be parallelized
        SystemServerInitThreadPool.get();
    } finally {
        traceEnd();  // InitBeforeStartServices
    }

    // Start services. 开启服务
    try {
        traceBeginAndSlog("StartServices");
        startBootstrapServices();//开启引导服务
        startCoreServices();//开启核心服务
        startOtherServices();//开启其他服务
        SystemServerInitThreadPool.shutdown();
    } catch (Throwable ex) {
        Slog.e("System", "******************************************");
        Slog.e("System", "************ Failure starting system services", ex);
        throw ex;
    } finally {
        traceEnd();
    }

    StrictMode.initVmDefaults(null);

    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);
        }
    }
    if (!VMRuntime.hasBootImageSpaces()) {
        Slog.wtf(TAG, "Runtime is not running with a boot image!");
    }

    // Loop forever.
    //loop启动
    Looper.loop();
    throw new RuntimeException("Main thread loop unexpectedly exited");
}

3,startBootstrapServices

开启了看门狗(用于监控system_server，一旦出现问题会杀死SystemServer，SystemServer撕掉会告诉Zygote Zygote接收到之后会杀死自己 然后告诉init init又会重启Zygote并且激活对应的onRestart)以及相当多的服务，其中有我们熟悉的Installer、ActivityTaskManagerService、ActivityManagerService、PowerManagerService、PackageManagerService等等，基本上就是通过startService方法

private void startBootstrapServices() {
    traceBeginAndSlog("StartWatchdog");
    final Watchdog watchdog = Watchdog.getInstance();
    watchdog.start();//开启看门狗
    traceEnd();

    Slog.i(TAG, "Reading configuration...");
    final String TAG_SYSTEM_CONFIG = "ReadingSystemConfig";
    traceBeginAndSlog(TAG_SYSTEM_CONFIG);
    SystemServerInitThreadPool.get().submit(SystemConfig::getInstance, TAG_SYSTEM_CONFIG);
    traceEnd();

    traceBeginAndSlog("StartInstaller");
    //开启Installer服务
    Installer installer = mSystemServiceManager.startService(Installer.class);
    traceEnd();

    traceBeginAndSlog("DeviceIdentifiersPolicyService");
    //开启设备标识符访问策略服务
    mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class);
    traceEnd();

    traceBeginAndSlog("UriGrantsManagerService");
    mSystemServiceManager.startService(UriGrantsManagerService.Lifecycle.class);
    traceEnd();

    // Activity manager runs the show.
    traceBeginAndSlog("StartActivityManager");
    //启动ActivityTaskManagerService、mActivityManagerService服务并关联systemServiceManager以及installer
    ActivityTaskManagerService atm = mSystemServiceManager.startService(
            ActivityTaskManagerService.Lifecycle.class).getService();
    mActivityManagerService = ActivityManagerService.Lifecycle.startService(
            mSystemServiceManager, atm);
    mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
    mActivityManagerService.setInstaller(installer);
    mWindowManagerGlobalLock = atm.getGlobalLock();
    traceEnd();

    // Power manager needs to be started early because other services need it.
    // Native daemons may be watching for it to be registered so it must be ready
    // to handle incoming binder calls immediately (including being able to verify
    // the permissions for those calls).
    traceBeginAndSlog("StartPowerManager");
    //开启PowerManagerService服务
    mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
    traceEnd();

    traceBeginAndSlog("StartThermalManager");
    mSystemServiceManager.startService(ThermalManagerService.class);
    traceEnd();

    // Now that the power manager has been started, let the activity manager
    // initialize power management features.
    traceBeginAndSlog("InitPowerManagement");
    mActivityManagerService.initPowerManagement();
    traceEnd();

    // Bring up recovery system in case a rescue party needs a reboot
    traceBeginAndSlog("StartRecoverySystemService");
    mSystemServiceManager.startService(RecoverySystemService.class);
    traceEnd();

    // Now that we have the bare essentials of the OS up and running, take
    // note that we just booted, which might send out a rescue party if
    // we're stuck in a runtime restart loop.
    RescueParty.noteBoot(mSystemContext);

    // Manages LEDs and display backlight so we need it to bring up the display.
    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(DisplayManagerService.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 = 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;
    }

    // Start the package manager.
    if (!mRuntimeRestart) {
        MetricsLogger.histogram(null, "boot_package_manager_init_start",
                (int) SystemClock.elapsedRealtime());
    }
    traceBeginAndSlog("StartPackageManagerService");
    try {
        Watchdog.getInstance().pauseWatchingCurrentThread("packagemanagermain");
        //创建PackageManagerService服务
        mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
                mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
    } finally {
        Watchdog.getInstance().resumeWatchingCurrentThread("packagemanagermain");
    }
    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 {
                Watchdog.getInstance().pauseWatchingCurrentThread("moveab");
                OtaDexoptService.main(mSystemContext, mPackageManagerService);
            } catch (Throwable e) {
                reportWtf("starting OtaDexOptService", e);
            } finally {
                Watchdog.getInstance().resumeWatchingCurrentThread("moveab");
                traceEnd();
            }
        }
    }

    traceBeginAndSlog("StartUserManagerService");
    mSystemServiceManager.startService(UserManagerService.LifeCycle.class);
    traceEnd();

    // Initialize attribute cache used to cache resources from packages.
    traceBeginAndSlog("InitAttributerCache");
    AttributeCache.init(mSystemContext);
    traceEnd();

    // Set up the Application instance for the system process and get started.
    traceBeginAndSlog("SetSystemProcess");
    mActivityManagerService.setSystemProcess();
    traceEnd();

    // Complete the watchdog setup with an ActivityManager instance and listen for reboots
    // Do this only after the ActivityManagerService is properly started as a system process
    traceBeginAndSlog("InitWatchdog");
    watchdog.init(mSystemContext, mActivityManagerService);
    traceEnd();

    // DisplayManagerService needs to setup android.display scheduling related policies
    // since setSystemProcess() would have overridden policies due to setProcessGroup
    mDisplayManagerService.setupSchedulerPolicies();

    // Manages Overlay packages
    traceBeginAndSlog("StartOverlayManagerService");
    mSystemServiceManager.startService(new OverlayManagerService(mSystemContext, installer));
    traceEnd();

    traceBeginAndSlog("StartSensorPrivacyService");
    mSystemServiceManager.startService(new SensorPrivacyService(mSystemContext));
    traceEnd();

    if (SystemProperties.getInt("persist.sys.displayinset.top", 0) > 0) {
        // DisplayManager needs the overlay immediately.
        mActivityManagerService.updateSystemUiContext();
        LocalServices.getService(DisplayManagerInternal.class).onOverlayChanged();
    }

    // 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);
}

4,startService

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);

        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);
        } 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);
        }
        //通过反射创建传递过来的Service对象，调用startService
        startService(service);
        return service;
    } finally {
        Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
    }
}

public void startService(@NonNull final SystemService service) {
        //将service添加到mServices中去
        mServices.add(service);
        long time = SystemClock.elapsedRealtime();
        try {
            //调用service的onStart函数启动对应的service
            service.onStart();
        } catch (RuntimeException ex) {
            throw new RuntimeException("Failed to start service " + service.getClass().getName()
                    + ": onStart threw an exception", ex);
        }
        warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart");
    }

拓展知识

LoadApk

LoadApk：理解为apk文件加载到内存的一个java对象 framework-res.apk

context 对于Android context 大家是怎么理解的？

LocalServices.java: addServece方法中 ArrayMap和HashMap的区别？

ArrayMap k,v k是int类型的包装，k是从小到大依次排列。时间复杂度可以是存的是 O(1). 取的过程就是log(n map.size). put和 get
HashMap <k(Object),v > 时间复杂度 put和 get O(1). K是一个复合类型，计算hash值 假如现在的k是String类型，那么就需要遍历当前字符串 计算当前“jijs”字符串的hash值存储到对应的位置上去 对应时间复杂度O(k) k复杂增长
ArrayList ?

AMS、PMS是谁启动的？他们都是独立的进程吗？

他们是由system_server启动，不是独立进程，他们都运行在system_server进程中。

WatchDog 看门狗机制？

原理：是一个单例模式，有一个handlerChecker集合，根据handler进行监控，监控所有的service 假如长时间未响应，AMS handler sendMessage（MQ）时间戳

简述system_server的启动

Zygote调用forkSystemServer来创建system_server进程，调用到Java层SystemServer.java.Main，创建SystemServer的ActivityThread 创建framewok-res.apk的Application调用onCreate，调用startBootstrapServices、startCoreServices、startOtherServices创建各种各样的Service（AMS、PMS等）,并开启开门狗检测服务和线程，如果出现问题就会杀死system_server，system_server死亡之后会通知Zygote,
Zygote会杀死自己 通知init, init有线程守护，会重启Zygote 并执行对应的onRestart服务。

总结

1.system_server是在Zygote启动的时候fork出来的子进程，调用的是ZygoteInit.forkSystemServer,最终返回MethodAndArgsCaller包装的是com.android.server.SystemServer.Main。

2.SystemServer.Main函数直接调用了run函数，在run函数中调用了createSystemContext通过ActivityThread.systemMain创建了ActivityThread，设置了mSystemContext并且调用ActivityThread.attach 通过反射创建Application 执行onCreate函数.这里创建的app是framewok-res.apk，是给系统使用的 比如系统的对话框。将mSystemServiceManager添加到LocalService的mService(ArrayMap)中去接着调用startBootstrapServices、startCoreServices、startOtherServices开启了非常多的服务Installer、ATMS、AMS、PMS等。把他们添加到SystemServiceManager的mServices(ArrayList)中去。