源码篇——安卓启动流程

首先说到的是安卓的四层架构：

 APPLICTION,

APPLICATION FRAMEWORK,

LIBRARICB+ANDROID RUNTIME,

LINUX KERNEL

android启动

当引导程序启动Linux内核后，会加载各种驱动和数据结构，当有了驱动以后，开始启动Android系统同时会加载用户级别的第一个进程init（system\core\init.c）代码如下：

    int main(int argc, char **argv){    // 创建文件夹 挂载    mount("tmpfs", "/dev", "tmpfs", 0, "mode=0755");    mkdir("/dev/pts", 0755);    // 打卡日志    log_init();    INFO("reading config file\n");    // 加载init.rc配置文件    init_parse_config_file("/init.rc");} 

加载init.rc文件，会启动一个Zygote进程，此进程是Android系统的一个母进程，用来启动Android的其他服务进程，代码：

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-serversocket zygote stream 666onrestart write /sys/android_power/request_state wakeonrestart write /sys/power/state ononrestart restart mediaonrestart restart netd

从c++代码调到java代码：

    int main(int argc, const char* const argv[]){    ...    // Android运行时环境    AppRuntime runtime;    ...    // Next arg is startup classname or "--zygote"    if (i < argc) {        arg = argv[i++];        if (0 == strcmp("--zygote", arg)) {            bool startSystemServer = (i < argc) ?                     strcmp(argv[i], "--start-system-server") == 0 : false;            setArgv0(argv0, "zygote");            set_process_name("zygote");            // 启动java代码            runtime.start("com.android.internal.os.ZygoteInit",         ...}

ZygoteInit.java 代码：

public static void main(String argv[]) { try { VMRuntime.getRuntime().setMinimumHeapSize(5 * 1024 * 1024);

        // 加载Android依赖的类        preloadClasses();        //cacheRegisterMaps();        preloadResources();        ...        if (argv[1].equals("true")) {            // 启动系统服务            startSystemServer();        } else if (!argv[1].equals("false")) {       ...}private static boolean startSystemServer()     ...        args = new String[] {            "--setuid=1000",            "--setgid=1000",            "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,3001,3002,3003,3006",            "--capabilities=130104352,130104352",            "--rlimit=8,",            "--runtime-init",            "--nice-name=system_server",            "com.android.server.SystemServer",      ...        /* Request to fork the system server process */        // 母进程开始分叉服务 启动SystemServer        pid = Zygote.forkSystemServer(                parsedArgs.uid, parsedArgs.gid,                parsedArgs.gids, debugFlags, rlimits,                parsedArgs.permittedCapabilities,                parsedArgs.effectiveCapabilities);    ..}

SystemServer.java 代码

public static void main(String[] args) {    ...     // 加载jni库    System.loadLibrary("android_servers");    // 调用native方法    init1(args);}native public static void init1(String[] args);

SystemServer 对应的c++代码 comandroidserver_SystemServer.cpp 代码如下：

// 类似java的抽象方法extern "C" int system_init();static void android_server_SystemServer_init1(JNIEnv* env, jobject clazz){       // 转调    system_init();}/* * JNI registration. */static JNINativeMethod gMethods[] = {    /* name, signature, funcPtr */     // 函数指针 把init1方法映射到android_server_SystemServer_init1    { "init1", "([Ljava/lang/String;)V", (void*) android_server_SystemServer_init1 },};

systeminit 的实现方法在Systeminit.cpp 代码如下：

extern "C" status_t system_init(){    ...    // 启动硬件的服务    if (strcmp(propBuf, "1") == 0) {        // Start the SurfaceFlinger        SurfaceFlinger::instantiate();    }    AndroidRuntime* runtime = AndroidRuntime::getRuntime();    LOGI("System server: starting Android services.\n");    // 启动完硬件服务后，又回到Systemserver的init2方法    runtime->callStatic("com/android/server/SystemServer", "init2");    ...}

SystemServer 的init2方法代码：

public static final void init2() {        Slog.i(TAG, "Entered the Android system server!");        Thread thr = new ServerThread();        thr.setName("android.server.ServerThread");        thr.start();    }

ServerThread的run方法：

public void run() { ... // 开启Android各种服务并且添加到ServiceManager去管理 Slog.i(TAG, "Device Policy"); devicePolicy = new DevicePolicyManagerService(context); ServiceManager.addService(Context.DEVICEPOLICYSERVICE, ottle =

    ...    // We now tell the activity manager it is okay to run third party    // code.  It will call back into us once it has gotten to the state    // where third party code can really run (but before it has actually    // started launching the initial applications), for us to complete our    // initialization.    // 各种服务开启后调用ActivityManagerService.systemReady    ((ActivityManagerService)ActivityManagerNative.getDefault())            .systemReady(new Runnable() {        public void run() {            Slog.i(TAG, "Making services ready");

ActivityMangerService的systemReady的方法：

public void systemReady(final Runnable goingCallback) {        ...        // 打开第一个Activity            mMainStack.resumeTopActivityLocked(null);        }    }

ActivityStack的resumeTopActivityLocked方法

final boolean resumeTopActivityLocked(ActivityRecord prev) {        // Find the first activity that is not finishing.        // 没有已经打开的Activity next为 null        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) {                // 启动lucher应用的锁屏界面                return mService.startHomeActivityLocked();            }        }

Android系统启动完成，打开了Luncher应用的Home界面。