Android启动流程

1. init进程

2. zygote进程

2.1 AndroidRuntime

2.2 ZygoteInit

3. system_server进程

3.1 init1阶段

3.2 init2阶段

接着Linux启动部分 http://blog.csdn.net/qianjin0703/article/details/6881107
1. init进程



系统在内核空间初始化进程，内存，文件系统，驱动模块之后，调用init_post()函数，开启第一个用户进程init，进入用户空间。

/kernel/init/main.c (仅截取部分重要代码)

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static noinline int init_post(void)

{



run_init_process("/sbin/init");

run_init_process("/etc/init");

run_init_process("/bin/init");

run_init_process("/bin/sh");

}

终端下查看1号进程，



可见，init是系统守护进程和zygote的父进程。

/system/core/init/init.c

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int main(int argc, char **argv)

{



mkdir("/dev", 0755);

mkdir("/proc", 0755);

mkdir("/sys", 0755);



mount("devpts", "/dev/pts", "devpts", 0, NULL);

mount("proc", "/proc", "proc", 0, NULL);

mount("sysfs", "/sys", "sysfs", 0, NULL);



open_devnull_stdio();

klog_init();

property_init();



get_hardware_name(hardware, &revision);

process_kernel_cmdline();



init_parse_config_file("/init.rc");

action_for_each_trigger("early-init", action_add_queue_tail);



queue_builtin_action(wait_for_coldboot_done_action, "wait_for_coldboot_done");

queue_builtin_action(keychord_init_action, "keychord_init");

queue_builtin_action(console_init_action, "console_init");

action_for_each_trigger("init", action_add_queue_tail);



for(;;) {



execute_one_command();

restart_processes();



nr = poll(ufds, fd_count, timeout);



for (i = 0; i < fd_count; i++) {

if (ufds[i].revents == POLLIN) {

if (ufds[i].fd == get_property_set_fd())

handle_property_set_fd();

else if (ufds[i].fd == get_keychord_fd())

handle_keychord();

else if (ufds[i].fd == get_signal_fd())

handle_signal();

}

}

}



return 0;

}

init进程归纳如下

解析init.rc和init.*.rc
挂载文件系统，建立文件夹和文件，设置权限，为一些文件写入初值
初始化property属性
启动系统守护进程如adbd, vold, rild等
启动zygote进程





2. zygote进程

zygote既是Android系统创建java世界的盘古，又是繁殖system_server和所有应用程序的女娲。

终端下查看zygote进程，



2.1 AndroidRuntime

/frameworks/base/cmds/app_process/app_main.cpp

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int main(int argc, const char* const argv[])

{



AppRuntime runtime;



if (zygote) {

runtime.start("com.android.internal.os.ZygoteInit",

startSystemServer ? "start-system-server" : "");

}

AppRuntime是从AndroidRuntime类派生的，最后由runtime.start()进入Java世界。

/frameworks/base/core/jni/AndroidRuntime.cpp

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void AndroidRuntime::start(const char* className, const char* options)

{



/* start the virtual machine */

JNIEnv* env;

if (startVm(&mJavaVM, &env) != 0) {

return;

}

onVmCreated(env);



/*

* Register android functions.

*/

if (startReg(env) < 0) {

ALOGE("Unable to register all android natives\n");

return;

}



/*

* Start VM. This thread becomes the main thread of the VM, and will

* not return until the VM exits.

*/

char* slashClassName = toSlashClassName(className);

jclass startClass = env->FindClass(slashClassName);



jmethodID startMeth = env->GetStaticMethodID(startClass, "main",

"([Ljava/lang/String;)V");



env->CallStaticVoidMethod(startClass, startMeth, strArray);



}

-> 创建虚拟机

注意这里会设置虚拟机的heapsize，默认16M，一般32M，不能太小，否则在操作大尺寸图片时无法分配所需内存。

-> 注册jni函数

这里注册了本地方法，这些方法最终被编译进动态链接库libandroid_runtime.so，供上层Java调用。

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static const RegJNIRec gRegJNI[] = {

REG_JNI(register_android_debug_JNITest),

REG_JNI(register_com_android_internal_os_RuntimeInit),

REG_JNI(register_android_os_SystemClock),

REG_JNI(register_android_util_Log),

REG_JNI(register_android_os_Process),

REG_JNI(register_android_os_SystemProperties),

REG_JNI(register_android_os_Binder),

REG_JNI(register_android_view_Display),

REG_JNI(register_android_graphics_Bitmap),

REG_JNI(register_android_graphics_Camera),

REG_JNI(register_android_database_SQLiteDatabase),

REG_JNI(register_android_os_Power),

REG_JNI(register_android_os_StatFs),

REG_JNI(register_android_net_NetworkUtils),

REG_JNI(register_android_nfc_NdefMessage),

REG_JNI(register_com_android_internal_os_ZygoteInit),

REG_JNI(register_android_hardware_Camera),

REG_JNI(register_android_hardware_SensorManager),

REG_JNI(register_android_hardware_UsbDevice),

REG_JNI(register_android_media_AudioRecord),

REG_JNI(register_android_media_AudioSystem),

REG_JNI(register_android_media_AudioTrack),

REG_JNI(register_android_opengl_classes),

REG_JNI(register_android_bluetooth_BluetoothSocket),

REG_JNI(register_android_server_BluetoothService),



REG_JNI(register_android_app_ActivityThread),

REG_JNI(register_android_app_NativeActivity),

REG_JNI(register_android_view_InputChannel),

REG_JNI(register_android_view_InputQueue),

REG_JNI(register_android_view_KeyEvent),

REG_JNI(register_android_view_MotionEvent),

REG_JNI(register_android_view_PointerIcon),



};

2.2 ZygoteInit

/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java

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public static void main(String argv[]) {

try {

SamplingProfilerIntegration.start();



registerZygoteSocket();



preload();



SamplingProfilerIntegration.writeZygoteSnapshot();



if (argv[1].equals("start-system-server")) {

startSystemServer();

}



runSelectLoopMode();



closeServerSocket();

}

}

-> 建立服务端Socket

zygote及系统中其他程序的通信没有使用Binder，而是采用了基于AF_UNIX类型的Socket.

-> 预加载类和资源

预加载的类可以在 /frameworks/base/preloaded-classes 查看。预加载的资源生成framewrok-res.apk，主要是一些图标，刷机达人经常修改它。

-> 启动system_server进程

zygote进程fork出system_server子进程，把任务繁重的系统服务全部托管出去，自己负责循环监听所有应用程序的请求。

-> 等待应用程序的请求

zygote通过runSelectLoopMode()处理应用程序客户端的请求，由ZygoteConnection的runOnce()孵化出新的应用程序。

综上所述，zygote进程归纳如下

创建虚拟机
注册jni函数
预加载类和资源
启动system_server进程
监听应用程序请求



3. system_server进程

/frameworks/base/services/java/com/android/SystemServer.java

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public static void main(String[] args) {



System.loadLibrary("android_servers");

init1(args);

}

3.1 init1阶段

加载libandriod_server.so库，实现init1

/frameworks/base/cmds/system_server/library/system_init.cpp

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extern "C" status_t system_init()

{



sp<GrimReaper> grim = new GrimReaper();

sm->asBinder()->linkToDeath(grim, grim.get(), 0);



char propBuf[PROPERTY_VALUE_MAX];

property_get("system_init.startsurfaceflinger", propBuf, "1");

if (strcmp(propBuf, "1") == 0) {

// Start the SurfaceFlinger

SurfaceFlinger::instantiate();

}



property_get("system_init.startsensorservice", propBuf, "1");

if (strcmp(propBuf, "1") == 0) {

// Start the sensor service

SensorService::instantiate();

}



AndroidRuntime* runtime = AndroidRuntime::getRuntime();



jclass clazz = env->FindClass("com/android/server/SystemServer");

jmethodID methodId = env->GetStaticMethodID(clazz, "init2", "()V");

env->CallStaticVoidMethod(clazz, methodId);



return NO_ERROR;

}



3.2 init2阶段

init2回到Java层，启动一个ServerThread线程，启动系统的各项服务。