大致流程
源码追踪
SystemServer启动
ZygoteInit.java
public static void main(String argv[]) {
try {
......
// 调用启动 SystemServer方法
if (startSystemServer) {
startSystemServer(abiList, socketName);
}
} catch (MethodAndArgsCaller caller) {
caller.run();
}
......
}
private static boolean startSystemServer(String abiList, String socketName)
throws MethodAndArgsCaller, RuntimeException {
... 参数准备
int pid;
try {
// 解析参数，生成目标格式
parsedArgs = new ZygoteConnection.Arguments(args);
ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);
ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);
// fork SystemServer 进程
pid = Zygote.forkSystemServer(
parsedArgs.uid, parsedArgs.gid,
parsedArgs.gids,
parsedArgs.debugFlags,
null,
parsedArgs.permittedCapabilities,
parsedArgs.effectiveCapabilities);
} catch (IllegalArgumentException ex) {
throw new RuntimeException(ex);
}
// 子进程 SystemServer
if (pid == 0) {
// 执行启动流程的剩余工作
handleSystemServerProcess(parsedArgs);
}
return true;
}
SystemServer进程fork
Zygote.java
public static int forkSystemServer(int uid, int gid, int[] gids, int debugFlags,
int[][] rlimits, long permittedCapabilities, long effectiveCapabilities) {
...
// 调用native方法fork system_server进程
int pid = nativeForkSystemServer(
uid, gid, gids, debugFlags, rlimits, permittedCapabilities, effectiveCapabilities);
...
return pid;
}
com_android_internal_os_Zygote.cpp
主要：fork创建新进程SystemServer，采用copy on write方式（为了高效先全部复制，等需要的时候在修改）另外， fork方法会有两次返回，分别返回子进程和父进程的pid
static jint com_android_internal_os_Zygote_nativeForkSystemServer(
JNIEnv* env, jclass, uid_t uid, gid_t gid, jintArray gids,
jint debug_flags, jobjectArray rlimits, jlong permittedCapabilities,
jlong effectiveCapabilities) {
// fork子进程，
pid_t pid = ForkAndSpecializeCommon(env, uid, gid, gids,
debug_flags, rlimits,
permittedCapabilities,effectiveCapabilities,
MOUNT_EXTERNAL_DEFAULT, NULL, NULL, true, NULL,NULL, NULL);
...
return pid;
}
static pid_t ForkAndSpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArray javaGids,
jint debug_flags, jobjectArray javaRlimits,
jlong permittedCapabilities, jlong effectiveCapabilities,
jint mount_external,
jstring java_se_info, jstring java_se_name,
bool is_system_server, jintArray fdsToClose,
jstring instructionSet, jstring dataDir) {
...
pid_t pid = fork(); //!!! fork子进程 (COW 方式)
if (pid == 0) { //进入子进程，初始化设置等
...
} else if (pid > 0) { //进入父进程，即zygote进程
...
}
return pid;
}
开始执行SystemServer进程fork后的ZygoteInit操作
ZygoteInit.java
private static void handleSystemServerProcess(
ZygoteConnection.Arguments parsedArgs)
throws ZygoteInit.MethodAndArgsCaller {
// 关闭父进程zygote复制而来的Socket
closeServerSocket();
if (parsedArgs.niceName != null) {
Process.setArgV0(parsedArgs.niceName); //设置当前进程名为"system_server"
}
final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
if (systemServerClasspath != null) {
// 执行dex优化操作
performSystemServerDexOpt(systemServerClasspath); }
if (parsedArgs.invokeWith != null) {
...
} else { // invokeWith = null
ClassLoader cl = null;
if (systemServerClasspath != null) {
创建类加载器，并赋予当前线程
cl = new PathClassLoader(systemServerClasspath, ClassLoader.getSystemClassLoader());
Thread.currentThread().setContextClassLoader(cl);
}
// RuntimeInit 执行 zygoteInit初始化工作
RuntimeInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
}
}
RuntimeInit.java
public static final void zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader)
throws ZygoteInit.MethodAndArgsCaller {
......
commonInit();
nativeZygoteInit();
applicationInit(targetSdkVersion, argv, classLoader);
}
private static final void commonInit() {
// 设置默认的未捕捉异常处理方法
Thread.setDefaultUncaughtExceptionHandler(new UncaughtHandler());
// 设置市区，中国时区为"Asia/Shanghai"
TimezoneGetter.setInstance(new TimezoneGetter() {
@Override
public String getId() {
return SystemProperties.get("persist.sys.timezone");
}
});
TimeZone.setDefault(null);
//重置log配置
LogManager.getLogManager().reset();
new AndroidConfig();
// 设置默认的HTTP User-agent格式,用于 HttpURLConnection。
String userAgent = getDefaultUserAgent();
System.setProperty("http.agent", userAgent);
// 设置socket的tag，用于网络流量统计
NetworkManagementSocketTagger.install();
}
// /frameworks/base/core/jni/AndroidRuntime.cpp
static void com_android_internal_os_RuntimeInit_nativeZygoteInit(JNIEnv* env, jobject clazz){
gCurRuntime->onZygoteInit();
}
// /frameworks/base/cmds/app_process/app_main.cpp
virtual void onZygoteInit(){
sp<ProcessState> proc = ProcessState::self();
proc->startThreadPool(); //启动新binder线程
}
private static void applicationInit(int targetSdkVersion, String[] argv, ClassLoader classLoader)
throws ZygoteInit.MethodAndArgsCaller {
...
//设置虚拟机的内存利用率参数值为0.75 , 设置目标sdk
VMRuntime.getRuntime().setTargetHeapUtilization(0.75f);
VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);
final Arguments args;
try {
args = new Arguments(argv); //解析参数
} catch (IllegalArgumentException ex) {
return;
}
// 调用startClass的static方法 main()；args.startClass为”com.android.server.SystemServer
invokeStaticMain(args.startClass, args.startArgs, classLoader);
}
private static void invokeStaticMain(String className, String[] argv, ClassLoader classLoader)
throws ZygoteInit.MethodAndArgsCaller {
Class<?> cl = Class.forName(className, true, classLoader);
Method m;
try {
m = cl.getMethod("main", new Class[] { String[].class });
} catch (Exception ex) {
...
}
int modifiers = m.getModifiers();
...
// ! 回到 ZygoteInit.main()方法中，直接进入catch语句（这样做好处是能清空栈帧，提高栈帧利用率，比较巧妙）
throw new ZygoteInit.MethodAndArgsCaller(m, argv);
}
ZygoteInit.java
public static void main(String argv[]) {
try {
startSystemServer(abiList, socketName);//启动system_server
....
} catch (MethodAndArgsCaller caller) {
caller.run();
} catch (RuntimeException ex) {
closeServerSocket();
throw ex;
}
}
public void run() {
try {
//根据传递过来的参数，可知此处通过反射机制调用的是SystemServer.main()方法
mMethod.invoke(null, new Object[] { mArgs });
...
}
}
SystemServer进程开始执行SystemServer.main方法
SystemServer.java
public static void main(String[] args) {
new SystemServer().run(); //创建SystemServer对象，再调用对象的run()方法
}
private void run() {
// 设置系统时间、设置默认语言、虚拟机库文件、虚拟机内存 等
...
// 当前线程作为mainLooper
Looper.prepareMainLooper();
// 初始化系统上下文
createSystemContext();
// 创建系统服务管理 用于创建和启动system service
mSystemServiceManager = new SystemServiceManager(mSystemContext);
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
// 启动各种系统服务
try {
startBootstrapServices(); // 启动引导服务
startCoreServices(); // 启动核心服务
startOtherServices(); // 启动其它服务
}
// 开启loop循环
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
private void createSystemContext() {
// 创建主线程任务的管理和调度类 ActivityThread
ActivityThread activityThread = ActivityThread.systemMain();
// 会依次创建对象有ActivityThread，Instrumentation, ContextImpl，LoadedApk，Application
}
依次启动引导服务、核心服务、其它服务
private void startBootstrapServices() {
//阻塞等待 Installer 建立socket通道
Installer installer = mSystemServiceManager.startService(Installer.class);
//启动服务 ActivityManagerService
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
//启动服务 PowerManagerService
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
mActivityManagerService.initPowerManagement();
//启动服务 LightsService
mSystemServiceManager.startService(LightsService.class);
//启动服务 DisplayManagerService
mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);
//Phase100: 服务启动阶段100 [100、480、500、550、600、1000]
mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
//启动服务 PackageManagerService
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
mFirstBoot = mPackageManagerService.isFirstBoot();
mPackageManager = mSystemContext.getPackageManager();
//启动服务 UserManagerService，新建目录/data/user/
ServiceManager.addService(Context.USER_SERVICE, UserManagerService.getInstance());
AttributeCache.init(mSystemContext);
//设置AMS
mActivityManagerService.setSystemProcess();
//启动传感器服务
startSensorService();
}
private void startCoreServices() {
//启动服务BatteryService，用于统计电池电量，需要LightService.
mSystemServiceManager.startService(BatteryService.class);
//启动服务UsageStatsService，用于统计应用使用情况
mSystemServiceManager.startService(UsageStatsService.class);
mActivityManagerService.setUsageStatsManager(
LocalServices.getService(UsageStatsManagerInternal.class));
mPackageManagerService.getUsageStatsIfNoPackageUsageInfo();
//启动服务WebViewUpdateService
mSystemServiceManager.startService(WebViewUpdateService.class);
}
private void startOtherServices() {
...
mContentResolver = context.getContentResolver(); // resolver
mActivityManagerService.installSystemProviders(); //provider
ActivityManagerNative.getDefault().showBootMessage(...); //显示启动界面
...
//phase480 和phase500 [100、480、500、550、600、1000]
mSystemServiceManager.startBootPhase(SystemService.PHASE_LOCK_SETTINGS_READY);
mSystemServiceManager.startBootPhase(SystemService.PHASE_SYSTEM_SERVICES_READY);
...
// 准备好 window, power, package, display服务
wm.systemReady();
mPowerManagerService.systemReady(...);
mPackageManagerService.systemReady();
mDisplayManagerService.systemReady(...);
// AMS ready 完成服务启动其它阶段 及Home启动等
mActivityManagerService.systemReady(new Runnable() {
public void run() {
//phase550
mSystemServiceManager.startBootPhase(
SystemService.PHASE_ACTIVITY_MANAGER_READY);
...
//phase600
mSystemServiceManager.startBootPhase(
SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);
...
}
});
}
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