Android系统启动流程-SystemServer分析

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SystemServer


  // 切换runtime,即dalvik 还是 art
  SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());

  Looper.prepareMainLooper();

  // 初始化native service
  System.loadLibrary("android_servers");

  // 初始化系统context.
  createSystemContext();

  //  创建 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();

  // 启动service
  startBootstrapServices();
  startCoreServices();
  startOtherServices();

  Looper.loop();

从上面的代码可以看出来,system_server主要做了下面这些事:

加载libandroid_servers.so

创建系统Context

创建SystemServiceManager,并添加到LocalServices中

依次启动启动服务,核心服务,和一些其他服务

在当前线程开启Looper机制

加载libandroid_servers.so

查看frameworks/base/services/Android.bp:


cc_library_shared {
    name: "libandroid_servers",
    defaults: ["libservices.core-libs"],
    whole_static_libs: ["libservices.core"],
}

可知libservices.core中的所有内容会链接到libandroid_servers中,而 libservices.core在frameworks/base/services/core/jni/下多个JNI文件:


cc_library_static {
    name: "libservices.core",
    defaults: ["libservices.core-libs"],

    srcs: [
        "BroadcastRadio/JavaRef.cpp",
        "BroadcastRadio/NativeCallbackThread.cpp",
        "BroadcastRadio/BroadcastRadioService.cpp",
        "BroadcastRadio/Tuner.cpp",
        "BroadcastRadio/TunerCallback.cpp",
        "BroadcastRadio/convert.cpp",
        "BroadcastRadio/regions.cpp",
        "com_android_server_AlarmManagerService.cpp",
        "com_android_server_adb_AdbDebuggingManager.cpp",
        "com_android_server_am_BatteryStatsService.cpp",
        "com_android_server_connectivity_Vpn.cpp",
        "com_android_server_ConsumerIrService.cpp",
        "com_android_server_devicepolicy_CryptoTestHelper.cpp",
        "com_android_server_HardwarePropertiesManagerService.cpp",
        "com_android_server_input_InputManagerService.cpp",
        "com_android_server_lights_LightsService.cpp",
        "com_android_server_location_GnssLocationProvider.cpp",
        "com_android_server_locksettings_SyntheticPasswordManager.cpp",
        "com_android_server_net_NetworkStatsService.cpp",
        "com_android_server_power_PowerManagerService.cpp",
        "com_android_server_security_VerityUtils.cpp",
        "com_android_server_SerialService.cpp",
        "com_android_server_storage_AppFuseBridge.cpp",
        "com_android_server_SystemServer.cpp",
        "com_android_server_TestNetworkService.cpp",
        "com_android_server_tv_TvUinputBridge.cpp",
        "com_android_server_tv_TvInputHal.cpp",
        "com_android_server_vr_VrManagerService.cpp",
        "com_android_server_UsbAlsaJackDetector.cpp",
        "com_android_server_UsbDeviceManager.cpp",
        "com_android_server_UsbDescriptorParser.cpp",
        "com_android_server_UsbMidiDevice.cpp",
        "com_android_server_UsbHostManager.cpp",
        "com_android_server_VibratorService.cpp",
        "com_android_server_PersistentDataBlockService.cpp",
        "com_android_server_GraphicsStatsService.cpp",
        "com_android_server_am_AppCompactor.cpp",
        "com_android_server_am_LowMemDetector.cpp",
        "onload.cpp",
        ":lib_networkStatsFactory_native",
    ],

    include_dirs: [
        "frameworks/base/libs",
        "frameworks/native/services",
        "system/gatekeeper/include",
    ],

    header_libs: [
        "bionic_libc_platform_headers",
    ],
}

cc_defaults {
    name: "libservices.core-libs",
    shared_libs: [
        "libadb_pairing_server",
        "libadb_pairing_connection",
        "libandroid_runtime",
        "libandroidfw",
        "libaudioclient",
        "libbase",
        "libappfuse",
        "libbinder",
        "libcutils",
        "libcrypto",
        "liblog",
        "libhardware",
        "libhardware_legacy",
        "libhidlbase",
        "libkeystore_binder",
        "libmtp",
        "libnativehelper",
        "libutils",
        "libui",
        "libinput",
        "libinputflinger",
        "libinputflinger_base",
        "libinputservice",
        "libschedulerservicehidl",
        "libsensorservice",
        "libsensorservicehidl",
        "libstatshidl",
	"libgui",
        "libusbhost",
        "libtinyalsa",
        "libEGL",
        "libGLESv2",
        "libnetutils",
        "libhidlbase",
        "libutils",
        "libhwui",
        "libbpf_android",
        "libnetdbpf",
        "libnetdutils",
        "libpsi",
        "android.hardware.audio.common@2.0",
        "android.hardware.broadcastradio@1.0",
        "android.hardware.broadcastradio@1.1",
        "android.hardware.contexthub@1.0",
        "android.hardware.gnss@1.0",
        "android.hardware.gnss@1.1",
        "android.hardware.gnss@2.0",
        "android.hardware.gnss.measurement_corrections@1.0",
        "android.hardware.gnss.visibility_control@1.0",
        "android.hardware.input.classifier@1.0",
        "android.hardware.ir@1.0",
        "android.hardware.light@2.0",
        "android.hardware.power@1.0",
        "android.hardware.power@1.1",
        "android.hardware.power.stats@1.0",
        "android.hardware.thermal@1.0",
        "android.hardware.tv.input@1.0",
        "android.hardware.vibrator-cpp",
        "android.hardware.vibrator@1.0",
        "android.hardware.vibrator@1.1",
        "android.hardware.vibrator@1.2",
        "android.hardware.vibrator@1.3",
        "android.hardware.vr@1.0",
        "android.frameworks.schedulerservice@1.0",
        "android.frameworks.sensorservice@1.0",
        "android.frameworks.stats@1.0",
	"android.system.suspend@1.0",
        "suspend_control_aidl_interface-cpp",
    ],

    static_libs: [
        "android.hardware.broadcastradio@common-utils-1x-lib",
    ],

    product_variables: {
        arc: {
            shared_libs: [
                "libarcbridge",
                "libarcbridgeservice",
                "libarctimer",
                "libbase",
                "libcap",
                "libchrome",
                "libmojo",
            ],
        }
    }
}

因此,这个so其实包含了frameworks/base/services/core/jni/下的内容.并且依赖了一些基础的so文件.

创建SystemContext 和SystemUiContext


    private void createSystemContext() {
        ActivityThread activityThread = ActivityThread.systemMain();
        mSystemContext = activityThread.getSystemContext();
        mSystemContext.setTheme(DEFAULT_SYSTEM_THEME);

        final Context systemUiContext = activityThread.getSystemUiContext();
        systemUiContext.setTheme(DEFAULT_SYSTEM_THEME);
    }

笼统的说,这个方法主要就是为了创建SystemContext和SystemUiContext. SystemContext和SystemUiContext都是ContextImpl对象,并且都是单例. 这里创建的SystemContext与SystemUiContext共享相同的LoadedApk,即context中的packageInfo.

这里创建ActivityThread的时候,会判断机型,如果是低端机,就禁止使用Thread Renderer:


    public static ActivityThread systemMain() {
        // The system process on low-memory devices do not get to use hardware
        // accelerated drawing, since this can add too much overhead to the
        // process.
        if (!ActivityManager.isHighEndGfx()) {
            ThreadedRenderer.disable(true);
        } else {
            ThreadedRenderer.enableForegroundTrimming();
        }
        ActivityThread thread = new ActivityThread();
        thread.attach(true, 0);
        return thread;
    }

attach的过程如下:


   private void attach(boolean system, long startSeq) {
        sCurrentActivityThread = this;
        mSystemThread = system;
        if (!system) {
            // 非system进程时执行这个分支
            android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
                                                    UserHandle.myUserId());
            RuntimeInit.setApplicationObject(mAppThread.asBinder());
            final IActivityManager mgr = ActivityManager.getService();
            try {
                mgr.attachApplication(mAppThread, startSeq);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            }
            // Watch for getting close to heap limit.
            BinderInternal.addGcWatcher(new Runnable() {
                @Override public void run() {
                    if (!mSomeActivitiesChanged) {
                        return;
                    }
                    Runtime runtime = Runtime.getRuntime();
                    long dalvikMax = runtime.maxMemory();
                    long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();
                    if (dalvikUsed > ((3*dalvikMax)/4)) {
                        if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024)
                                + " total=" + (runtime.totalMemory()/1024)
                                + " used=" + (dalvikUsed/1024));
                        mSomeActivitiesChanged = false;
                        try {
                            ActivityTaskManager.getService().releaseSomeActivities(mAppThread);
                        } catch (RemoteException e) {
                            throw e.rethrowFromSystemServer();
                        }
                    }
                }
            });
        } else {
            // system_server进程时执行这个分支
            android.ddm.DdmHandleAppName.setAppName("system_process",
                    UserHandle.myUserId());
            try {
                mInstrumentation = new Instrumentation();
                mInstrumentation.basicInit(this);
                ContextImpl context = ContextImpl.createAppContext(
                        this, getSystemContext().mPackageInfo);
                mInitialApplication = context.mPackageInfo.makeApplication(true, null);
                mInitialApplication.onCreate();
            } catch (Exception e) {
                throw new RuntimeException(
                        "Unable to instantiate Application():" + e.toString(), e);
            }
        }

        ViewRootImpl.ConfigChangedCallback configChangedCallback
                = (Configuration globalConfig) -> {
            synchronized (mResourcesManager) {
                // We need to apply this change to the resources immediately, because upon returning
                // the view hierarchy will be informed about it.
                if (mResourcesManager.applyConfigurationToResourcesLocked(globalConfig,
                        null /* compat */)) {
                    updateLocaleListFromAppContext(mInitialApplication.getApplicationContext(),
                            mResourcesManager.getConfiguration().getLocales());

                    // This actually changed the resources! Tell everyone about it.
                    if (mPendingConfiguration == null
                            || mPendingConfiguration.isOtherSeqNewer(globalConfig)) {
                        mPendingConfiguration = globalConfig;
                        sendMessage(H.CONFIGURATION_CHANGED, globalConfig);
                    }
                }
            }
        };
        ViewRootImpl.addConfigCallback(configChangedCallback);
    }

ActiviyThread的主要作用是:

管理应用进程的主线程执行

调度,执行activity,broadcast和其他操作

attach的这个操作会创建一个AppContext(其实也是ContextImpl对象),并通过LoadedApk创建一个默认的Application(android.app.Application).

创建SystemServiceManager

创建SystemServiceManager,然后将其添加到一个Map中,后续统一处理.

启动各种服务

分成三类服务:

BootStrap

Core

Other

所有服务均是SystemService的实现类,通过SystemServiceManager启动服务的时候,会调用service的onStart()方法启动服务.

Bootstrap Service

WatchDog 其实就是一个Thread对象,当启动过程中发生死锁,可以使system_server崩溃

Installer 使用之前创建的SystemServiceManager对象启动Installer Service. Installer service在启动的时候会通过Binder机制请求installd(一个守护进程,用于安装apk)

DeviceIdentifiersPolicyService 定义访问设备标识符的策略

UriGrantsManagerService.LifeCyle 管理Uri授权

ActivityTaskManagerService.Lifecycle 管理Activity和Activity的容器,比如task, stacks, displays等

ActivityManagerService

PowerManagerService

ThermalManagerService

RecoverySystemService

LightsService

SidekickService

DisplayManagerService

UserManagerService

OverlayManagerService

SensorPrivacyService

Core Service

BatteryService

UsageStatsService

WebViewUpdateService

CachedDeviceStateService

BinderCallsStatsService.LifeCycle

RollbackManagerService

BugreportManagerService

GpuService

Other Service

VibratorService

DynamicSystemService

NetworkManagementService

IpSecService

NetworkStatsService

NetworkPolicyManagerService

ConnectivityService

NsdService

WindowManagerService

SerialService

NetworkTimeUpdateService

InputManagerService

ConsumerIrService

HardwarePropertiesManagerService

UiModeManagerService

ContentCaptureService

AttentionService

SystemCaptionsManagerService

AdbService

PermissionPolicyService ...

在启动Other类服务的最后阶段会执行mActivityManagerService.systemReady() 这个方法中会执行一些方法的systemReady方法,并启动System UI.

启动System UI


    private static void startSystemUi(Context context, WindowManagerService windowManager) {
        Intent intent = new Intent();
        intent.setComponent(new ComponentName("com.android.systemui",
                "com.android.systemui.SystemUIService"));
        intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
        //Slog.d(TAG, "Starting service: " + intent);
        context.startServiceAsUser(intent, UserHandle.SYSTEM);
        windowManager.onSystemUiStarted();
    }

有关System UI相关的内容可以参考:

SystemUI

实现System UI