第二步android系统启动:入口为init.rc(system\core\rootdir)
1./system/bin/service manager: Binder 守护进程;
2.Runtime;
3.Zygote :app-process/app-main;
4.Start VM;
5.Start server
6.Start android service:Register to service Manager
7.Start Launcher
第三步:应用程序启动:运行package Manager
1.Init进程
Android系统在启动时首先会启动Linux系统,引导加载Linux Kernel并启动init进程。Init进程是一个由内核启动的用户级进程,是Android系统的第一个进程。该进程的相关代码在system\core\init\init.c。在main函数中,有如下代码:
- open_devnull_stdio();
- log_init();
- INFO("reading config file\n");
- init_parse_config_file("/init.rc");
- /* pull the kernel commandline and ramdisk properties file in */
- import_kernel_cmdline(0);
- get_hardware_name(hardware, &revision);
- snprintf(tmp, sizeof(tmp), "/init.%s.rc", hardware);
- init_parse_config_file(tmp);
这里会加载解析init.rc和init.hardware.rc两个初始化脚本。*.rc文件定义了在init进程中需要启动哪些进程服务和执行哪些动作。其详细说明参见system\core\init\reademe.txt。init.rc见如下定义:
- service servicemanager /system/bin/servicemanager
- user system
- critical
- onrestart restart zygote
- onrestart restart media
- service vold /system/bin/vold
- socket vold stream 0660 root mount
- ioprio be 2
- service netd /system/bin/netd
- socket netd stream 0660 root system
- socket dnsproxyd stream 0660 root inet
- service debuggerd /system/bin/debuggerd
- service ril-daemon /system/bin/rild
- socket rild stream 660 root radio
- socket rild-debug stream 660 radio system
- user root
- group radio cache inet misc audio sdcard_rw
- service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
- socket zygote stream 666
- onrestart write /sys/android_power/request_state wake
- onrestart write /sys/power/state on
- onrestart restart media
- onrestart restart netd
- service drm /system/bin/drmserver
- user drm
- group system root inet
具体解析过程见system\core\init\Init_parser.c。解析所得服务添加到service_list中,动作添加到action_list中。
接下来在main函数中执行动作和启动进程服务:
- execute_one_command();
- restart_processes();
通常init过程需要创建一些系统文件夹并启动USB守护进程、Android Debug Bridge守护进程、Debug守护进程、ServiceManager进程、Zygote进程等。
2. ServiceManager进程
ServiceManager进程是所有服务的管理器。由init.rc对ServiceManager的描述service servicemanager /system/bin/servicemanager可知servicemanager进程从frameworks/base/cmds/servicemanager/service_manager.c启动。在main函数中有如下代码:
- int main(int argc, char **argv)
- {
- struct binder_state *bs;
- void *svcmgr = BINDER_SERVICE_MANAGER;
- bs = binder_open(128*1024);
- if (binder_become_context_manager(bs)) {
- LOGE("cannot become context manager (%s)\n", strerror(errno));
- return -1;
- }
- svcmgr_handle = svcmgr;
- binder_loop(bs, svcmgr_handler);
- return 0;
- }
首先调用binder_open()打开Binder设备(/dev/binder),调用binder_become_context_manager()把当前进程设置为ServiceManager。ServiceManager本身就是一个服务。
- int binder_become_context_manager(struct binder_state *bs)
- {
- return ioctl(bs->fd, BINDER_SET_CONTEXT_MGR, 0);
- }
最后binder_loop()进入循环状态,并设置svcmgr_handler回调函数等待添加、查询、获取服务等请求。
3. Zygote进程
Zygote进程用于产生其他进程。由init.rc对zygote的描述service zygot /system/bin/app_process可知zygote进程从platfrom\frameworks\base\cmds\app_process\App_main.cpp启动。在main函数中有如下代码:
- if (0 == strcmp("--zygote", arg)) {
- bool startSystemServer = (i < argc) ?
- strcmp(argv[i], "--start-system-server") == 0 : false;
- setArgv0(argv0, "zygote");
- set_process_name("zygote");
- runtime.start("com.android.internal.os.ZygoteInit",
- startSystemServer);
- } else {
- set_process_name(argv0);
- runtime.mClassName = arg;
- // Remainder of args get passed to startup class main()
- runtime.mArgC = argc-i;
- runtime.mArgV = argv+i;
- LOGV("App process is starting with pid=%d, class=%s.\n",
- getpid(), runtime.getClassName());
- runtime.start();
- }
首先创建AppRuntime,即AndroidRuntime,建立了一个Dalvik虚拟机。通过这个runtime传递com.android.internal.os.ZygoteInit参数,从而由Dalvik虚拟机运行ZygoteInit.java的main(),开始创建Zygote进程。在其main()中,如下所示:
- registerZygoteSocket();
- EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
- SystemClock.uptimeMillis());
- preloadClasses();
- //cacheRegisterMaps();
- preloadResources();
- EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
- SystemClock.uptimeMillis());
- // Finish profiling the zygote initialization.
- SamplingProfilerIntegration.writeZygoteSnapshot();
- // Do an initial gc to clean up after startup
- gc();
- // If requested, start system server directly from Zygote
- if (argv.length != 2) {
- throw new RuntimeException(argv[0] + USAGE_STRING);
- }
- if (argv[1].equals("true")) {
- startSystemServer();
- } else if (!argv[1].equals("false")) {
- throw new RuntimeException(argv[0] + USAGE_STRING);
- }
首先通过registerZygoteSocket()登记端口,接着preloadClasses()装载相关类。这里大概要装载1000多个类,具体装载类见frameworks\base\preloaded-classes。这个文件有WritePreloadedClassFile类自动生成。分析该类的main函数,有如下一段筛选类的代码:
- // Preload classes that were loaded by at least 2 processes. Hopefully,
- // the memory associated with these classes will be shared.
- for (LoadedClass loadedClass : root.loadedClasses.values()) {
- Set<String> names = loadedClass.processNames();
- if (!Policy.isPreloadable(loadedClass)) {
- continue;
- }
- if (names.size() >= MIN_PROCESSES ||
- (loadedClass.medianTimeMicros() > MIN_LOAD_TIME_MICROS && names.size() > 1)) {
- toPreload.add(loadedClass);
- }
- }
- int initialSize = toPreload.size();
- System.out.println(initialSize
- + " classses were loaded by more than one app.");
- // Preload eligable classes from applications (not long-running
- // services).
- for (Proc proc : root.processes.values()) {
- if (proc.fromZygote() && !Policy.isService(proc.name)) {
- for (Operation operation : proc.operations) {
- LoadedClass loadedClass = operation.loadedClass;
- if (shouldPreload(loadedClass)) {
- toPreload.add(loadedClass);
- }
- }
- }
- }
其中MIN_LOAD_TIME_MICROS等于1250,当类的装载时间大于1.25ms,则需要预装载。
Policy.isPreloadable()定于如下:
- /**Reports if the given class should be preloaded. */
- public static boolean isPreloadable(LoadedClass clazz) {
- return clazz.systemClass && !EXCLUDED_CLASSES.contains(clazz.name);
- }
其中EXCLUDED_CLASSES如下定义:
- /**
- * Classes which we shouldn't load from the Zygote.
- */
- private static final Set<String> EXCLUDED_CLASSES
- = new HashSet<String>(Arrays.asList(
- // Binders
- "android.app.AlarmManager",
- "android.app.SearchManager",
- "android.os.FileObserver",
- "com.android.server.PackageManagerService$AppDirObserver",
- // Threads
- "android.os.AsyncTask",
- "android.pim.ContactsAsyncHelper",
- "java.lang.ProcessManager"
- ));
这几个Binders和Thread是不会被预加载的。
另外还有一些application需要装载,要求满足条件proc.fromZygote()且不是属于常驻内存的服务。SERVICES定义如下:
- /**
- * Long running services. These are restricted in their contribution to the
- * preloader because their launch time is less critical.
- */
- // TODO: Generate this automatically from package manager.
- private static final Set<String> SERVICES = new HashSet<String>(Arrays.asList(
- "system_server",
- "com.google.process.content",
- "android.process.media",
- "com.android.bluetooth",
- "com.android.calendar",
- "com.android.inputmethod.latin",
- "com.android.phone",
- "com.google.android.apps.maps.FriendService", // pre froyo
- "com.google.android.apps.maps:FriendService", // froyo
- "com.google.android.apps.maps.LocationFriendService",
- "com.google.android.deskclock",
- "com.google.process.gapps",
- "android.tts"
- ));
preloaded-classes是在下载源码的时候生成,WritePreloadedClassFile类并没有被用到,但可以通过这个类了解Android系统对预加载类的默认要求,参考修改preloaded-classes文件,减少开机初始化时要预加载的类,提高开机速度。
最后(还在ZygoteInit.java的main函数里)来通过startSystemServer()启动SystemServer进程。见如下代码:
- /* Hardcoded command line to start the system server */
- String args[] = {
- "--setuid=1000",
- "--setgid=1000",
- "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,3001,3002,3003",
- "--capabilities=130104352,130104352",
- "--runtime-init",
- "--nice-name=system_server",
- "com.android.server.SystemServer",
- };
- ZygoteConnection.Arguments parsedArgs = null;
- int pid;
- try {
- parsedArgs = new ZygoteConnection.Arguments(args);
- /*
- * Enable debugging of the system process if *either* the command line flags
- * indicate it should be debuggable or the ro.debuggable system property
- * is set to "1"
- */
- int debugFlags = parsedArgs.debugFlags;
- if ("1".equals(SystemProperties.get("ro.debuggable")))
- debugFlags |= Zygote.DEBUG_ENABLE_DEBUGGER;
- /* Request to fork the system server process */
- pid = Zygote.forkSystemServer(
- parsedArgs.uid, parsedArgs.gid,
- parsedArgs.gids, debugFlags, null,
- parsedArgs.permittedCapabilities,
- parsedArgs.effectiveCapabilities)
Zygote包装了Linux的fork。forkSystemServer()调用forkAndSpecialize()(android4.1中是别的函数),最终穿过虚拟机调用platform\dalvik\vm\native\dalvik_system_Zygote.cpp中Dalvik_dalvik_system_Zygote_forkAndSpecialize()。由dalvik完成fork新的进程。
main()最后会调用runSelectLoopMode(),进入while循环,由peers创建新的进程。
4. SystemService进程
SystemService用于创建init.rc定义的服务之外的所有服务。在SystemServer.java (frameworks\base\services\java\com\android\server) 的main()的最后有如下代码:
- // 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);
- System.loadLibrary("android_servers");
- init1(args);
Init1()是在native空间实现的,用于启动native空间的服务,其实现在com_android_server_SystemServer.cpp中的android_server_SystemServer_init1():
- static void android_server_SystemServer_init1(JNIEnv* env, jobject clazz)
- {
- system_init();
- }
而system_init()(System_init.cpp (frameworks\base\cmds\system_server\library)文件中)服务初始化创建native层的各个服务:
- // Start the sensor service
- SensorService::instantiate();
- // On the simulator, audioflinger et al don't get started the
- // same way as on the device, and we need to start them here
- if (!proc->supportsProcesses()) {
- // Start the AudioFlinger
- AudioFlinger::instantiate();
- // Start the media playback service
- MediaPlayerService::instantiate();
- // Start the camera service
- CameraService::instantiate();
- // Start the audio policy service
- AudioPolicyService::instantiate();
- }
最后通过如下代码: (android4.1略有区别)
- LOGI("System server: starting Android services.\n");
- runtime->callStatic("com/android/server/SystemServer", "init2");
回到SystemServer.java,调用init2():
- public static final void init2() {
- Slog.i(TAG, "Entered the Android system server!");
- Thread thr = new ServerThread();
- thr.setName("android.server.ServerThread");
- thr.start();
- }
Init2启动一个线程,专门用来启动java空间的所有服务。如下代码所示启动部分服务:
- // Critical services...
- try {
- Slog.i(TAG, "Entropy Service");
- ServiceManager.addService("entropy", new EntropyService());
- Slog.i(TAG, "Power Manager");
- power = new PowerManagerService();
- ServiceManager.addService(Context.POWER_SERVICE, power);
- Slog.i(TAG, "Activity Manager");
- context = ActivityManagerService.main(factoryTest);
- Slog.i(TAG, "Telephony Registry");
- ServiceManager.addService("telephony.registry", new TelephonyRegistry(context));
- AttributeCache.init(context);
- Slog.i(TAG, "Package Manager");
- // Only run "core" apps if we're encrypting the device.
- String cryptState = SystemProperties.get("vold.decrypt");
- boolean onlyCore = false;
- if (ENCRYPTING_STATE.equals(cryptState)) {
- Slog.w(TAG, "Detected encryption in progress - only parsing core apps");
- onlyCore = true;
- } else if (ENCRYPTED_STATE.equals(cryptState)) {
- Slog.w(TAG, "Device encrypted - only parsing core apps");
- onlyCore = true;
- }
- pm = PackageManagerService.main(context,
- factoryTest != SystemServer.FACTORY_TEST_OFF,
- onlyCore);
- boolean firstBoot = false;
- try {
- firstBoot = pm.isFirstBoot();
- } catch (RemoteException e) {
- }
- ActivityManagerService.setSystemProcess();
- mContentResolver = context.getContentResolver();
- // The AccountManager must come before the ContentService
- try {
- Slog.i(TAG, "Account Manager");
- ServiceManager.addService(Context.ACCOUNT_SERVICE,
- new AccountManagerService(context));
- } catch (Throwable e) {
- Slog.e(TAG, "Failure starting Account Manager", e);
- }
- Slog.i(TAG, "Content Manager");
- ContentService.main(context,
- factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL);
- Slog.i(TAG, "System Content Providers");
- ActivityManagerService.installSystemProviders();
- Slog.i(TAG, "Lights Service");
- lights = new LightsService(context);
- Slog.i(TAG, "Battery Service");
- battery = new BatteryService(context, lights);
- ServiceManager.addService("battery", battery);
- Slog.i(TAG, "Vibrator Service");
- ServiceManager.addService("vibrator", new VibratorService(context));
- // only initialize the power service after we have started the
- // lights service, content providers and the battery service.
- power.init(context, lights, ActivityManagerService.self(), battery);
- Slog.i(TAG, "Alarm Manager");
- alarm = new AlarmManagerService(context);
- ServiceManager.addService(Context.ALARM_SERVICE, alarm);
- Slog.i(TAG, "Init Watchdog");
- Watchdog.getInstance().init(context, battery, power, alarm,
- ActivityManagerService.self());
- Slog.i(TAG, "Window Manager");
- wm = WindowManagerService.main(context, power,
- factoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL,
- !firstBoot);
- ServiceManager.addService(Context.WINDOW_SERVICE, wm);
- ActivityManagerService.self().setWindowManager(wm);
- // Skip Bluetooth if we have an emulator kernel
- // TODO: Use a more reliable check to see if this product should
- // support Bluetooth - see bug 988521
- if (SystemProperties.get("ro.kernel.qemu").equals("1")) {
- Slog.i(TAG, "No Bluetooh Service (emulator)");
- } else if (factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL) {
- Slog.i(TAG, "No Bluetooth Service (factory test)");
- } else {
- Slog.i(TAG, "Bluetooth Service");
- bluetooth = new BluetoothService(context);
- ServiceManager.addService(BluetoothAdapter.BLUETOOTH_SERVICE, bluetooth);
- bluetooth.initAfterRegistration();
- bluetoothA2dp = new BluetoothA2dpService(context, bluetooth);
- ServiceManager.addService(BluetoothA2dpService.BLUETOOTH_A2DP_SERVICE,
- bluetoothA2dp);
- bluetooth.initAfterA2dpRegistration();
- int airplaneModeOn = Settings.System.getInt(mContentResolver,
- Settings.System.AIRPLANE_MODE_ON, 0);
- int bluetoothOn = Settings.Secure.getInt(mContentResolver,
- Settings.Secure.BLUETOOTH_ON, 0);
- if (airplaneModeOn == 0 && bluetoothOn != 0) {
- bluetooth.enable();
- }
- }
- } catch (RuntimeException e) {
- Slog.e("System", "******************************************");
- Slog.e("System", "************ Failure starting core service", e);
- }
并且把这些服务添加到ServiceManager中,以便管理和进程间通讯。
在该线程后半部分,ActivityManagerService会等待AppWidget、WallPaper、IMM等systemReady后调用自身的systemReady()。
- Slog.i(TAG, "Content Manager");
- ContentService.main(context,
- factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL);
- ((ActivityManagerService)ServiceManager.getService("activity"))
- .setWindowManager(wm);
- // Skip Bluetooth if we have an emulator kernel
- // TODO: Use a more reliable check to see if this product should
- // support Bluetooth - see bug 988521
- if (SystemProperties.get("ro.kernel.qemu").equals("1")) {
- Slog.i(TAG, "Registering null Bluetooth Service (emulator)");
- ServiceManager.addService(BluetoothAdapter.BLUETOOTH_SERVICE, null);
- } else if (factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL) {
- Slog.i(TAG, "Registering null Bluetooth Service (factory test)");
- ServiceManager.addService(BluetoothAdapter.BLUETOOTH_SERVICE, null);
- } else {
- Slog.i(TAG, "Bluetooth Service");
- bluetooth = new BluetoothService(context);
- ServiceManager.addService(BluetoothAdapter.BLUETOOTH_SERVICE, bluetooth);
- bluetooth.initAfterRegistration();
- bluetoothA2dp = new BluetoothA2dpService(context, bluetooth);
- ServiceManager.addService(BluetoothA2dpService.BLUETOOTH_A2DP_SERVICE,
- bluetoothA2dp);
- int bluetoothOn = Settings.Secure.getInt(mContentResolver,
- Settings.Secure.BLUETOOTH_ON, 0);
- if (bluetoothOn > 0) {
- bluetooth.enable();
- }
- }
而在ActivityManagerService的systemReady()最后会执行如下代码:
- mMainStack.resumeTopActivityLocked(null);
由于Activity管理栈为空,因此启动Launcher。
- // Find the first activity that is not finishing.
- ActivityRecord next = topRunningActivityLocked(null);
- // Remember how we'll process this pause/resume situation, and ensure
- // that the state is reset however we wind up proceeding.
- final boolean userLeaving = mUserLeaving;
- mUserLeaving = false;
- if (next == null) {
- // There are no more activities! Let's just start up the
- // Launcher...
- if (mMainStack) {
- return mService.startHomeActivityLocked();
- }
- }
在startHomeActivityLocked()中创建一个带Category为CATEGORY_HOME的Intent,由此去启动相应Activity,即Launcher。
- Intent intent = new Intent(
- mTopAction,
- mTopData != null ? Uri.parse(mTopData) : null);
- intent.setComponent(mTopComponent);
- if (mFactoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL) {
- intent.addCategory(Intent.CATEGORY_HOME);
- }
这样,Android系统便启动起来进入到待机界面。