Android FrameWork（三）SystemServer（下）_systemserverinitthreadpool: shutdown requested

    上次说到，从Zygote.forkSystemServer()一直到SystemServer.main()。这篇博客，将从SystemServer的main方法开始说起。没看过SystemServer（一）的可以先去看一下：Android FrameWork之SystemServer（一）

 一.SystemServer.main()

    首先，SystemServer.java的路径如下：/frameworks/base/services/java/com/android/server/SystemServer.java。我们看一下其main()方法：

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

    非常简短的方法，创建一个SystemServerd对象，然后调用其run()方法。

二.SystemServer.run()

    run()方法是一个很长的方法，其实也还好，注释占了很大一部分篇幅，源码如下：

    private void run() {
        try {
            traceBeginAndSlog("InitBeforeStartServices");
            // If a device's clock is before 1970 (before 0), a lot of
            // APIs crash dealing with negative numbers, notably
            // java.io.File#setLastModified, so instead we fake it and
            // hope that time from cell towers or NTP fixes it shortly.
            if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
                Slog.w(TAG, "System clock is before 1970; setting to 1970.");
                SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
            }
 
            //
            // Default the timezone property to GMT if not set.
            //
            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 the system has "persist.sys.language" and friends set, replace them with
            // "persist.sys.locale". Note that the default locale at this point is calculated
            // using the "-Duser.locale" command line flag. That flag is usually populated by
            // AndroidRuntime using the same set of system properties, but only the system_server
            // and system apps are allowed to set them.
            //
            // NOTE: Most changes made here will need an equivalent change to
            // core/jni/AndroidRuntime.cpp
            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", "");
            }
 
            // The system server should never make non-oneway calls
            Binder.setWarnOnBlocking(true);
            // The system server should always load safe labels
            PackageItemInfo.setForceSafeLabels(true);
            // Deactivate SQLiteCompatibilityWalFlags until settings provider is initialized
            SQLiteCompatibilityWalFlags.init(null);
 
            // Here we go!
            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);
            }
 
            // In case the runtime switched since last boot (such as when
            // the old runtime was removed in an OTA), set the system
            // property so that it is in sync. We can | xq oqi't do this in
            // libnativehelper's JniInvocation::Init code where we already
            // had to fallback to a different runtime because it is
            // running as root and we need to be the system user to set
            // the property. http://b/11463182
            SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());
 
            // Mmmmmm... more memory!
            VMRuntime.getRuntime().clearGrowthLimit();
 
            // The system server has to run all of the time, so it needs to be
            // as efficient as possible with its memory usage.
            VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
 
            // Some devices rely on runtime fingerprint generation, so make sure
            // we've defined it before booting further.
            Build.ensureFingerprintProperty();
 
            // Within the system server, it is an error to access Environment paths without
            // explicitly specifying a user.
            Environment.setUserRequired(true);
 
            // Within the system server, any incoming Bundles should be defused
            // to avoid throwing BadParcelableException.
            BaseBundle.setShouldDefuse(true);
 
            // Within the system server, when parceling exceptions, include the stack trace
            Parcel.setStackTraceParceling(true);
 
            // Ensure binder calls into the system always run at foreground priority.
            BinderInternal.disableBackgroundScheduling(true);
 
            // Increase the number of binder threads in system_server
            BinderInternal.setMaxThreads(sMaxBinderThreads);
 
            // Prepare the main looper thread (this thread).
            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);
 
            // 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.setStartInfo(mRuntimeRestart,
                    mRuntimeStartElapsedTime, mRuntimeStartUptime);
            LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
            // Prepare the thread pool for init tasks that can be parallelized
            SystemServerInitThreadPool.get();
        } finally {
            traceEnd();  // InitBeforeStartServices
        }
 
        // Start services.
        try {
            traceBeginAndSlog("StartServices");
            startBootstrapServices();
            startCoreServices();
            startOtherServices();
            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);
            }
        }
 
        // Loop forever.
        Looper.loop();
        throw new RuntimeException("Main thread loop unexpectedly exited");
    }

    run()方法主要做了哪些工作？让我们一起跟着源码和注释分析一下：

    （1）如果系统时间早于1970年，则设置系统时间为1970年

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

    （2）如果时区没有设置，设置时区为GMT(格林尼治标准时间)

if (timezoneProperty == null || timezoneProperty.isEmpty()) {
                Slog.w(TAG, "Timezone not set; setting to GMT.");
                SystemProperties.set("persist.sys.timezone", "GMT");
            }

    （3）设置语言，国家，地区等（只有system server或者系统app才能修改）

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", "");
            }

    （4）变更库文件，因为默认使用的是libart.so

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

    （5）清除内存增长上限，为启动过程提供更多的内存空间

VMRuntime.getRuntime().clearGrowthLimit();

    （6）设置内存可能的利用率为0.8

VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);

    （7）在开机完成前定义指纹信息

Build.ensureFingerprintProperty();

    （8）设置Binder的优先级和最大线程数

BinderInternal.disableBackgroundScheduling(true);
 
BinderInternal.setMaxThreads(sMaxBinderThreads);

    （9）准备主线程Looper

// Prepare the main looper thread (this thread).
            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);

    （10）初始化系统上下文

createSystemContext();

    （11）创建System Service Manager

mSystemServiceManager = new SystemServiceManager(mSystemContext);
            mSystemServiceManager.setStartInfo(mRuntimeRestart,
                    mRuntimeStartElapsedTime, mRuntimeStartUptime);
            LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);

     （12）启动各种系统服务

traceBeginAndSlog("StartServices");
            startBootstrapServices();
            startCoreServices();
            startOtherServices();
            SystemServerInitThreadPool.shutdown();

    （13）循环执行

// Loop forever.
        Looper.loop();

三.startBootstrapServices()

    做的主要工作是启动一些服务，例如我们常说的：ActivityManagerService, PowerManagerService,DisplayManagerService， PackageManagerService等。

/**
     * 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();
 
        // Wait for installd to finish starting up so that it has a chance to
        // create critical directories such as /data/user with the appropriate
        // permissions.  We need this to complete before we initialize other services.
        traceBeginAndSlog("StartInstaller");
        Installer installer = mSystemServiceManager.startService(Installer.class);
        traceEnd();
 
        // In some cases after launching an app we need to access device identifiers,
        // therefore register the device identifier policy before the activity manager.
        traceBeginAndSlog("DeviceIdentifiersPolicyService");
        mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class);
        traceEnd();
 
        // Activity manager runs the show.
        traceBeginAndSlog("StartActivityManager");
        mActivityManagerService = mSystemServiceManager.startService(
                ActivityManagerService.Lifecycle.class).getService();
        mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
        mActivityManagerService.setInstaller(installer);
        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");
        mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.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 = 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;
        }
 
        // Start the package manager.
        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();
                }
            }
        }
 
        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();
 
        // 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();
 
        // 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);
    }

四.startCoreServices

     启动一些核心的服务：BatteryService，UsageStatsService，WebViewUpdateService。

    /**
     * Starts some essential services that are not tangled up in the bootstrap process.
     */
    private void startCoreServices() {
        traceBeginAndSlog("StartBatteryService");
        // Tracks the battery level.  Requires LightService.
        mSystemServiceManager.startService(BatteryService.class);
        traceEnd();
 
        // Tracks application usage stats.
        traceBeginAndSlog("StartUsageService");
        mSystemServiceManager.startService(UsageStatsService.class);
        mActivityManagerService.setUsageStatsManager(
                LocalServices.getService(UsageStatsManagerInternal.class));
        traceEnd();
 
        // Tracks whether the updatable WebView is in a ready state and watches for update installs.
        if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_WEBVIEW)) {
            traceBeginAndSlog("StartWebViewUpdateService");
            mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class);
            traceEnd();
        }
 
        // Tracks cpu time spent in binder calls
        traceBeginAndSlog("StartBinderCallsStatsService");
        BinderCallsStatsService.start();
        traceEnd();
    }

    SystemServer还会启动一些其他的服务，代码太多，不再一一去看。

    最后，总结一下。System Server是zygote进程fork的第一个进程，是android 基本服务的提供者，FrameWork关键的系统服务全由此创建而来。可以说，整个android系统的业务都是围绕system server而展开。一旦SystemServer挂了，整个手机系统也就挂了。