android 啟動的流程

Linux

BootLoader 作用-> 加載驅動啟動硬體加載linux核心

系統的第一個程序 init 程序對應的啟動的代碼 init.c

system/core/init/init.c

main方法

建立重要的系統目錄并且加載進來

mkdir("/dev", 0755);

mkdir("/proc", 0755);

mkdir("/sys", 0755);

mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");

mkdir("/dev/pts", 0755);

mkdir("/dev/socket", 0755);

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

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

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

init_parse_config_file("/init.rc"); //解析init.rc配置檔案這個配置檔案中都是linux指令解析這些指令并且執行

system/core/rootdir/init.rc

跟啟動相關比較重要的部分

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server

class main

socket zygote stream 660 root system

onrestart write /sys/android_power/request_state wake

onrestart write /sys/power/state on

onrestart restart media

onrestart restart netd

以服務的形式啟動 zygote程序

zygote程序是android中十分重要的程序孵化器程序(受精卵) 所有的android應用程序以及重要的系統程序都是有這個zygote程序通過fork

以複制自身的形式建立的

1.service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server

2.service zygote 以服務的形式啟動zygote

3./system/bin/app_process 啟動的時候對應的檔案路徑

--zygote --start-system-server啟動是傳入的參數

App_main.cpp

main方法

......

const char* className = NULL;

while (i < argc) {

const char* arg = argv[i++];

if (!parentDir) {

parentDir = arg;

} else if (strcmp(arg, "--zygote") == 0) {//周遊傳入的字元串數組 --zygote --start-system-server

zygote = true;

niceName = "zygote"; //這裡會被執行

} else if (strcmp(arg, "--start-system-server") == 0) {

startSystemServer = true; //這裡會被執行

} else if (strcmp(arg, "--application") == 0) {

application = true;

} else if (strncmp(arg, "--nice-name=", 12) == 0) {

niceName = arg + 12;

} else {

className = arg;

break;

}

if (niceName && *niceName) {

setArgv0(argv0, niceName);

set_process_name(niceName); //給目前程序起名字為zygote

}

runtime.mParentDir = parentDir;

if (zygote) {

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

startSystemServer ? "start-system-server" : ""); //調用runtime.start方法(ZygoteInit start-system-server)

}

....

runtime.start("com.android.internal.os.ZygoteInit", "start-system-server" );

runtime.start ①給目前的程序建立了一個java虛拟機 ②通過jni的調用啟動了ZygoteInit.java的main方法啟動了第一個java程式

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

{

ALOGD("\n>>>>>> AndroidRuntime START %s <<<<<<\n",

className != NULL ? className : "(unknown)");

blockSigpipe();

if (strcmp(options, "start-system-server") == 0) {

const int LOG_BOOT_PROGRESS_START = 3000;

LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START,

ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));

}

const char* rootDir = getenv("ANDROID_ROOT");

if (rootDir == NULL) {

rootDir = "/system";

if (!hasDir("/system")) {

LOG_FATAL("No root directory specified, and /android does not exist.");

return;

}

setenv("ANDROID_ROOT", rootDir, 1);

}

//const char* kernelHack = getenv("LD_ASSUME_KERNEL");

//ALOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack);

JNIEnv* env; //啟動java虛拟機

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

return;

}

onVmCreated(env);

if (startReg(env) < 0) {

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

return;

}

jclass stringClass;

jobjectArray strArray;

jstring classNameStr;

jstring optionsStr;

stringClass = env->FindClass("java/lang/String"); 通過jni調用建立了一個java的String[] = {"com.android.internal.os.ZygoteInit", "start-system-server"}

assert(stringClass != NULL);

strArray = env->NewObjectArray(2, stringClass, NULL);

assert(strArray != NULL);

classNameStr = env->NewStringUTF(className);

assert(classNameStr != NULL);

env->SetObjectArrayElement(strArray, 0, classNameStr);

optionsStr = env->NewStringUTF(options);

env->SetObjectArrayElement(strArray, 1, optionsStr);

char* slashClassName = toSlashClassName(className); //通過Jni調用找到zygoteInit.java的位元組碼找到main方法執行

jclass startClass = env->FindClass(slashClassName);

if (startClass == NULL) {

ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);

} else {

jmethodID startMeth = env->GetStaticMethodID(startClass, "main", //執行main方法的時候把剛建立的String[]作為參數穿進去

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

if (startMeth == NULL) {

ALOGE("JavaVM unable to find main() in '%s'\n", className);

} else {

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

#if 0

if (env->ExceptionCheck())

threadExitUncaughtException(env);

#endif

}

free(slashClassName);

ALOGD("Shutting down VM\n");

if (mJavaVM->DetachCurrentThread() != JNI_OK)

ALOGW("Warning: unable to detach main thread\n");

if (mJavaVM->DestroyJavaVM() != 0)

ALOGW("Warning: VM did not shut down cleanly\n");

}

到這兒從native世界來到了java的程式中

zygoteInit main方法

public static void main(String argv[]) {

try {

// Start profiling the zygote initialization.

SamplingProfilerIntegration.start();

registerZygoteSocket(); //建立一個socket服務端

EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,

SystemClock.uptimeMillis());

preload(); //預加載資源包括兩千多個位元組碼對象用到的系統圖檔顔色資源

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("start-system-server")) {

startSystemServer(); //開啟SystemServer 系統服務

} else if (!argv[1].equals("")) {

throw new RuntimeException(argv[0] + USAGE_STRING);

}

Log.i(TAG, "Accepting command socket connections");

if (ZYGOTE_FORK_MODE) {

runForkMode();

} else {

runSelectLoopMode(); //開啟死循環等待socket用戶端通路

}

closeServerSocket();

} catch (MethodAndArgsCaller caller) {

caller.run();

} catch (RuntimeException ex) {

Log.e(TAG, "Zygote died with exception", ex);

closeServerSocket();

throw ex;

}

zygote啟動到這兒就結束了

zygote在啟動的過程中做了如下幾件事兒

① zygote程序建立了一個jvm

② zygote建立了一個socket服務端等待ams給它發消息分叉新的程序

③ 預加載了資源包括位元組碼圖檔顔色

④ 跑起死循環等待用戶端連接配接

⑤ 建立了SystemServer程序

SystemServer啟動的過程

private static boolean startSystemServer()

throws MethodAndArgsCaller, RuntimeException {

String args[] = {

"--setuid=1000",

"--setgid=1000",

"--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,3001,3002,3003,3006,3007",

"--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); //zygote程序分叉出systemserver程序

ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);

ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);

pid = Zygote.forkSystemServer(

parsedArgs.uid, parsedArgs.gid,

parsedArgs.gids,

parsedArgs.debugFlags,

null,

parsedArgs.permittedCapabilities,

parsedArgs.effectiveCapabilities);

} catch (IllegalArgumentException ex) {

throw new RuntimeException(ex);

}

if (pid == 0) {

handleSystemServerProcess(parsedArgs); //pid為0說明目前的代碼執行在子程序中這個程序就是system_server程序

}

return true;

}

hanldeSystemServerProess->RuntimeInit.zygoteInit->applicationInit->invokestaticMain()->調用了SystemServer.java的main方法

systemServer的main方法通過jni調用到 systemserver.cpp的init1方法

init1方法調用了system_init() 在這個方法中把顯示的驅動和傳感器的驅動啟動起來

隻有這些驅動加載進來了在java層才能啟動相應的服務

通過jni system_init() 方法又調用到systemServer.java的 init2方法

public static final void init2() {

Slog.i(TAG, "Entered the Android system server!");

Thread thr = new ServerThread();

thr.setName("android.server.ServerThread");

thr.start(); //執行serverThread的run方法

}

在run方法中建立了系統服務對象通過ServiceManager儲存起來

.....//聲明各種服務

Installer installer = null;

AccountManagerService accountManager = null;

ContentService contentService = null;

LightsService lights = null;

PowerManagerService power = null;

DisplayManagerService display = null;

BatteryService battery = null;

VibratorService vibrator = null;

AlarmManagerService alarm = null;

MountService mountService = null;

NetworkManagementService networkManagement = null;

NetworkStatsService networkStats = null;

NetworkPolicyManagerService networkPolicy = null;

ConnectivityService connectivity = null;

WifiP2pService wifiP2p = null;

WifiService wifi = null;

NsdService serviceDiscovery= null;

//建立服務通過ServiceManager管理以key-value的形式添加到ServiceManger中

//是以 getSystemService(傳入一個字元串) 傳回服務

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, "Display Manager");

display = new DisplayManagerService(context, wmHandler, uiHandler);

ServiceManager.addService(Context.DISPLAY_SERVICE, display, true);

Slog.i(TAG, "Telephony Registry");

telephonyRegistry = new TelephonyRegistry(context);

ServiceManager.addService("telephony.registry", telephonyRegistry);

Slog.i(TAG, "Scheduling Policy");

ServiceManager.addService(Context.SCHEDULING_POLICY_SERVICE,

new SchedulingPolicyService());

當所有的服務都添加進去之後會執行ActivityManagerService的systemready方法

mMainStack.resumeTopActivityLocked(null);//判斷目前的主任務棧是否有activity 如果沒有就啟動桌面

final boolean resumeTopActivityLocked(ActivityRecord prev, Bundle options) {

// 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) {

ActivityOptions.abort(options);

return mService.startHomeActivityLocked(mCurrentUser);

}

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