Android启动流程
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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。
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