Android开机流程

Zygote进程
在init.rc中有
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
zygote进程通过init进程启动，zygote进程就奠定了Android的基础。
从zygote的main()开始，见/frameworks/base/cmds/app_process/app_main.cpp
int main(int argc, const char * const argv[])
{
 ......
 if(0 == strcmp("--zygote", arg)){
  ......
  runtime.start("com.android.internel.os.ZygoteInit",
   startSystemServer);
 ......
}
接下来运行/frameworks/base/core/jni/AndroidRuntime.cpp的start()
void AndroidRuntime::start(const char * className, const bool startSystemServer)
{
 ......
 classNameStr = env->NewStringUTF(className);
 ......
 startMeth = env->GetStaticMethodID(startClass, "main",
         "([Ljava/lang/String;)V");
 ......
}
因此运行/frameworks/base/java/com/android/internal/os/ZygoteInit.java的main().
public static void main(String argv[]){
 ......
 registerZygoteSocket();
 preloadClasses();
 if(argc[1].equals("true")){
  startSystemServer();
 }
 ......

}
在startSystemServer()有
private static boolean startSystemServer(){
 ......
  pid = Zygote.forkSystemServer(
   parseArgs.uid, parseArgs.gid,
   parseArgs.gids, debugFlags, null)
 ......
 if(pid == 0)
 {
  handleSystemServerProcess(parseArgs);
 }
} 
private static void handleSystemServerProcess(
        ZygoteConnection.Arguments parsedArgs)
        throws ZygoteInit.MethodAndArgsCaller {
 ......
 RuntimeInit.zygoteInit(parsedArgs.remainingArgs);
} 
在zygoteInit(String[] argv)@/frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
依次调用zygoteNative()@/frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
invokeStaticMain() @/frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
在invokeStaticMain()中
        m = cl.getMethod("main", new Class[] { String[].class });
执行的是SystemServer类main函数
public static void main(String[] args){
  ......
        System.loadLibrary("android_servers");
        init1(args);
}
init1依次调用
android_server_SystemServer_init1()@ /frameworks/base/services/jni/com_android_server_SystemServer.cpp
system_init() @/frameworks/base/cmds/system_server/library/System_init.cpp
extern "C" status_t system_init()
{
    sp<ProcessState> proc(ProcessState::self());
    sp<IServiceManager> sm = defaultServiceManager();

    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) {
  SurfaceFlinger::instantiate();
    }

    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();
    }
   
    AndroidRuntime* runtime = AndroidRuntime::getRuntime();

    runtime->callStatic("com/android/server/SystemServer", "init2");
       
    if (proc->supportsProcesses()) {
        LOGI("System server: entering thread pool./n");
        ProcessState::self()->startThreadPool();
        IPCThreadState::self()->joinThreadPool();
        LOGI("System server: exiting thread pool./n");
    }
    return NO_ERROR;
}
在system_init()初始化AudioFlinger, MediaPlayerService, CameraService, AudioPolicyService等,最后由如下
    runtime->callStatic("com/android/server/SystemServer", "init2")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();
    }
最后运行ServerThread的run.
在run中启动电源管理、蓝牙等核心服务以及状态。 
在ServerThread后半段，启动完所有Android服务后，使用xxx.systemReady()通知个服务，系统已经就绪。
ActivityManagerService.systemReady()中依次调用resumeTopActivityLocked()和startHomeActivityLocked().
如果是第一个则启动HomeActivity.
private boolean startHomeActivityLocked() {
    if (mFactoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL
            && mTopAction == null) {
         return false;
    }
    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);
        }
        ActivityInfo aInfo =
            intent.resolveActivityInfo(mContext.getPackageManager(),
                    STOCK_PM_FLAGS);
        if (aInfo != null) {
            intent.setComponent(new ComponentName(
                    aInfo.applicationInfo.packageName, aInfo.name));
        ProcessRecord app = getProcessRecordLocked(aInfo.processName,
                aInfo.applicationInfo.uid);
        if (app == null || app.instrumentationClass == null) {
                intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
            startActivityLocked(null, intent, null, null, 0, aInfo,
                    null, null, 0, 0, 0, false, false);
        }
    }
    return true;
}
这是"android.process.acore"进程。

在启动的时候, ActivityManagerService.systemReady将启动所有常驻应用. 如下：
List apps = ActivityThread.getPackageManager().
getPersistentApplications(PackageManager.GET_SHARED_LIBRARY_FILES);
if (apps != null) {
 int N = apps.size();
 int i;
 for (i=0; i<N; i++) {
 ApplicationInfo info
  = (ApplicationInfo)apps.get(i);
  if (info != null &&
   !info.packageName.equals("android")) {
  addAppLocked(info);
  }
 }
}
常驻应用在AndroidManifest.xml中有android:persistent="true"