Android系统源码分析--Zygote和SystemServer启动过程
按计划原本从这章开始写四大组件的启动过程的，可是看看源码结构发现为了说的更明白仍是先写一点系统framework层启动的内容，帮助理解四大组件的启动以及管理过程。咱们知道四大组件管理是经过一些服务以及线程实现的，因此先把一些基本概念弄清楚比较好，好比AMS（ActivityManagerService）、PMS（PackageManagerService）等系统服务的做用以及调用方式，了解这些以后再看四大组件相对容易些，所以咱们本章先介绍系统启动、部分系统服务的做用。java
Zygote启动过程
Zygote是一个孕育器，Android系统全部的应用进程以及系统服务SystemServer都是有Zygote进程孕育（fork）而生的，所以Zygote在Android启动过程当中起着决定做用。Zygote的启动是从它的main函数开始的，所以咱们从这个函数开始分析。整个过程看下面的时序图。android
下面咱们开始根据时序图进行分析。git
Step 0.ZygoteInit.main缓存
public static void main(String argv[]) {
...
try {
...
registerZygoteSocket(socketName);
...
preload();
...
gcAndFinalize();
...
if (startSystemServer) {
startSystemServer(abiList, socketName);
}
runSelectLoop(abiList);
closeServerSocket();
} catch (MethodAndArgsCaller caller) {
...
} catch (Throwable ex) {
...
}
}复制代码
首先调用registerZygoteSocket方法，建立一个socket接口，用来和ActivityManagerService通信，而后调用preload方法预加载一些资源等；而后调用gcAndFinalize方法释放一些内存；而后调用startSystemServer方法启动SystemServer组件，而后调用runSelectLoop方法，建立一个无限循环，在socket接口上等待ActivityManagerService请求建立新的应用程序进程；最后调用closeServerSocket方法关闭上面建立的socket。微信
Step 1.ZygoteInit.registerZygoteSocketapp
private static void registerZygoteSocket(String socketName) {
if (sServerSocket == null) {
int fileDesc;
final String fullSocketName = ANDROID_SOCKET_PREFIX + socketName;
try {
String env = System.getenv(fullSocketName);
fileDesc = Integer.parseInt(env);
} catch (RuntimeException ex) {
...
}
try {
FileDescriptor fd = new FileDescriptor();
fd.setInt$(fileDesc);
sServerSocket = new LocalServerSocket(fd);
} catch (IOException ex) {
throw new RuntimeException(
"Error binding to local socket '" + fileDesc + "'", ex);
}
}
}复制代码
这个sServerSocket是经过传入FileDescriptor（文件描述者）经过new一个来LocalServerSocket建立的。socket
Step 2.LocalServerSocket函数
public LocalServerSocket(FileDescriptor fd) throws IOException {
impl = new LocalSocketImpl(fd);
impl.listen(LISTEN_BACKLOG);
localAddress = impl.getSockAddress();
}复制代码
在LocalServerSocket构造函数中又new了一个LocalSocketImpl，而后调用LocalSocketImpl的listen方法，最后经过getSockAddress方法获取LocalSocketAddress对象。oop
Step 3.LocalSocketImpl源码分析
/*package*/ LocalSocketImpl(FileDescriptor fd) throws IOException
{
this.fd = fd;
}复制代码
这里只是传入了FileDescriptor（文件描述者）。
Step 5.ZygoteInit.preload
static void preload() {
...
beginIcuCachePinning();
...
preloadClasses();
...
preloadResources();
...
preloadOpenGL();
...
preloadSharedLibraries();
preloadTextResources();
...
}复制代码
这里主要是预加载，1.预加载ICU缓存，2.执行Zygote进程初始化，预加载一些普通类，3.预加载mResources，4.预加载OpenGL，5.预加载共享库，6.预加载TextView的字体缓存。
Step 12.ZygoteInit.gcAndFinalize
/*package*/ static void gcAndFinalize() {
final VMRuntime runtime = VMRuntime.getRuntime();
...
System.gc();
runtime.runFinalizationSync();
System.gc();
}复制代码
这里主要是调用System.gc来释放一部份内存。
Step 13.ZygoteInit.startSystemServer
private static boolean startSystemServer(String abiList, String socketName) throws MethodAndArgsCaller, RuntimeException {
...
int pid;
try {
...
/* Request to fork the system server process */
pid = Zygote.forkSystemServer(
parsedArgs.uid, parsedArgs.gid,
parsedArgs.gids,
parsedArgs.debugFlags,
null,
parsedArgs.permittedCapabilities,
parsedArgs.effectiveCapabilities);
} catch (IllegalArgumentException ex) {
...
}
/* For child process */
if (pid == 0) {
if (hasSecondZygote(abiList)) {
waitForSecondaryZygote(socketName);
}
handleSystemServerProcess(parsedArgs);
}
return true;
}复制代码
首先Zygote会经过调用Zygote.forkSystemServer方法来建立一个新的进程来启动SystemServer，而且返回这个进程的pid，若是pid为0，而且有另一个Zygote则会执行waitForSecondaryZygote关闭另外的Zygote进程，而后调用handleSystemServerProcess方法。
Step 16.ZygoteInit.handleSystemServerProcess
private static void handleSystemServerProcess( ZygoteConnection.Arguments parsedArgs) throws ZygoteInit.MethodAndArgsCaller {
closeServerSocket();
...
final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
if (systemServerClasspath != null) {
performSystemServerDexOpt(systemServerClasspath);
}
if (parsedArgs.invokeWith != null) {
...
} else {
...
RuntimeInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
}
}复制代码
首先调用closeServerSocket方法关闭socket，而后调用performSystemServerDexOpt来建立安装链接InstallerConnection，最后调用RuntimeInit.zygoteInit方法。
Step 19.RuntimeInit.zygoteInit
public static final void zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) throws ZygoteInit.MethodAndArgsCaller {
...
nativeZygoteInit();
applicationInit(targetSdkVersion, argv, classLoader);
}复制代码
首先调用nativeZygoteInit函数来执行一个Binder进程间通信机制初始化工做，而后就能够在进程间进行通信了，而后执行applicationInit方法。
Step 21.RuntimeInit.applicationInit
private static void applicationInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) throws ZygoteInit.MethodAndArgsCaller {
...
invokeStaticMain(args.startClass, args.startArgs, classLoader);
}复制代码
这里主要是执行一个invokeStaticMain方法来调用SystemServer的main方法。
Step 24.ZygoteInit.runSelectLoop
private static void runSelectLoop(String abiList) throws MethodAndArgsCaller {
ArrayList<FileDescriptor> fds = new ArrayList<FileDescriptor>();
ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>();
fds.add(sServerSocket.getFileDescriptor());
peers.add(null);
while (true) {
...
try {
Os.poll(pollFds, -1);
} catch (ErrnoException ex) {
...
}
for (int i = pollFds.length - 1; i >= 0; --i) {
if ((pollFds[i].revents & POLLIN) == 0) {
continue;
}
if (i == 0) {
ZygoteConnection newPeer = acceptCommandPeer(abiList);
peers.add(newPeer);
fds.add(newPeer.getFileDesciptor());
} else {
boolean done = peers.get(i).runOnce();
if (done) {
peers.remove(i);
fds.remove(i);
}
}
}
}
}复制代码
这里经过acceptCommandPeer来建立ActivityManagerService与Socket的链接，而后调用ZygoteConnection.runOnce方法来建立新的应用程序。
SystemServer启动过程
咱们从上面的Step 13 知道了SystemServer的main函数调用位置，下面咱们分析一下SystemServer的启动过程。
在main方法中new了一个SystemServer而后调用它的run方法：
private void run() {
try {
...
// Mmmmmm... more memory!
// 清除vm内存增加上限，因为启动过程须要较多的虚拟机内存空间
VMRuntime.getRuntime().clearGrowthLimit();
// The system server has to run all of the time, so it needs to be
// as efficient as possible with its memory usage.
// 设置内存的可能有效使用率为0.8
VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
// Some devices rely on runtime fingerprint generation, so make sure
// we've defined it before booting further.
Build.ensureFingerprintProperty();
// Within the system server, it is an error to access Environment paths without
// explicitly specifying a user.
// 访问环境变量前，须要明确地指定用户
Environment.setUserRequired(true);
// Within the system server, any incoming Bundles should be defused
// to avoid throwing BadParcelableException.
BaseBundle.setShouldDefuse(true);
// Ensure binder calls into the system always run at foreground priority.
// 确保当前系统进程的binder调用，老是运行在前台优先级(foreground priority)
BinderInternal.disableBackgroundScheduling(true);
// Increase the number of binder threads in system_server
BinderInternal.setMaxThreads(sMaxBinderThreads);
...
// 准备主线程的Looper
Looper.prepareMainLooper();
// Initialize native services.
// 加载android_servers.so库，该库包含的源码在frameworks/base/services/目录下
System.loadLibrary("android_servers");
// Check whether we failed to shut down last time we tried.
// This call may not return.
performPendingShutdown();
// Initialize the system context.
// 初始化系统上下文
createSystemContext();
// Create the system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);
//将mSystemServiceManager添加到本地服务的成员sLocalServiceObjects
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
} finally {
...
}
// Start services.
try {
...
startBootstrapServices(); // 启动引导服务
startCoreServices(); // 启动核心服务
startOtherServices(); // 启动其余服务
} catch (Throwable ex) {
...
} finally {
...
}
...
// Loop（循环） forever.
Looper.loop();
...
}复制代码
Step 3.Build.ensureFingerprintProperty
public static void ensureFingerprintProperty() {
if (TextUtils.isEmpty(SystemProperties.get("ro.build.fingerprint"))) {
try {
SystemProperties.set("ro.build.fingerprint", FINGERPRINT);
} catch (IllegalArgumentException e) {
Slog.e(TAG, "Failed to set fingerprint property", e);
}
}
}复制代码
确认设备的指纹属性。
Step 7.Looper.prepareMainLooper()
public static void prepareMainLooper() {
prepare(false);
synchronized (Looper.class) {
if (sMainLooper != null) {
throw new IllegalStateException("The main Looper has already been prepared.");
}
sMainLooper = myLooper();
}
}复制代码
准备main looper，这个详细的过程咱们下一章再讲，这里先看一下流程。
Step 10.SystemServer.performPendingShutdown
private void performPendingShutdown() {
final String shutdownAction = SystemProperties.get(
ShutdownThread.SHUTDOWN_ACTION_PROPERTY, "");
if (shutdownAction != null && shutdownAction.length() > 0) {
// 是否重启
boolean reboot = (shutdownAction.charAt(0) == '1');
final String reason;
if (shutdownAction.length() > 1) {
reason = shutdownAction.substring(1, shutdownAction.length());
} else {
reason = null;
}
if (PowerManager.REBOOT_RECOVERY_UPDATE.equals(reason)) {
File packageFile = new File(UNCRYPT_PACKAGE_FILE);
if (packageFile.exists()) {
String filename = null;
try {
filename = FileUtils.readTextFile(packageFile, 0, null);
} catch (IOException e) {
Slog.e(TAG, "Error reading uncrypt package file", e);
}
if (filename != null && filename.startsWith("/data")) {
if (!new File(BLOCK_MAP_FILE).exists()) {
...
return;
}
}
}
}
ShutdownThread.rebootOrShutdown(null, reboot, reason);
}
}复制代码
这里主要是经过关机的action来判断是否重启或者关机。
Step 13.SystemServer.createSystemContext
private void createSystemContext() {
// 初始化ActivityThread，并设置默认主题
ActivityThread activityThread = ActivityThread.systemMain();
mSystemContext = activityThread.getSystemContext();
mSystemContext.setTheme(DEFAULT_SYSTEM_THEME);
}复制代码
首先调用ActivityThread.systemMain方法建立ActivityThread对象而后获取mSystemContext，而且设置默认系统主题。
Step 15.ActivityThread.systemMain
public static ActivityThread systemMain() {
...
ActivityThread thread = new ActivityThread();
thread.attach(true);
return thread;
}复制代码
建立ActivityThread对象，并调用attach方法。
Step 17.ResourcesManager.getInstance
public static ResourcesManager getInstance() {
synchronized (ResourcesManager.class) {
if (sResourcesManager == null) {
sResourcesManager = new ResourcesManager();
}
return sResourcesManager;
}复制代码
单例模式建立ResourcesManager对象而且返回。
Step 19.ActivityThread.attach
private void attach(boolean system) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
...
} else {
...
try {
mInstrumentation = new Instrumentation();
ContextImpl context = ContextImpl.createAppContext(
this, getSystemContext().mPackageInfo);
mInitialApplication = context.mPackageInfo.makeApplication(true, null);
mInitialApplication.onCreate();
} catch (Exception e) {
...
}
}
...
}复制代码
由于参数传入的是true，代表是系统的线程，因此执行else里面的内容，首先建立Instrumentation，而后调用ContextImpl.createAppContext方法建立ContextImpl，而后经过调用LoadedApk.makeApplication方法建立Application，而后调用Application.onCreate方法。
Step 22.ContextImpl.createAppContext
static ContextImpl createAppContext(ActivityThread mainThread, LoadedApk packageInfo) {
if (packageInfo == null) throw new IllegalArgumentException("packageInfo");
return new ContextImpl(null, mainThread,
packageInfo, null, null, 0, null, null, Display.INVALID_DISPLAY);
}复制代码
经过new ContextImpl来建立ContextImpl对象。
Step 22.LoadedApk.makeApplication
public Application makeApplication(boolean forceDefaultAppClass, Instrumentation instrumentation) {
...
Application app = null;
...
try {
...
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
} catch (Exception e) {
...
}
...
if (instrumentation != null) {
try {
instrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
...
}
}
...
return app;
}复制代码
经过ContextImpl.createAppContext方法建立ContextImpl对象，而后调用mActivityThread.mInstrumentation.newApplication方法建立Application对象，而后调用instrumentation.callApplicationOnCreate方法。
Step 23.ContextImpl.createAppContext
static ContextImpl createAppContext(ActivityThread mainThread, LoadedApk packageInfo) {
if (packageInfo == null) throw new IllegalArgumentException("packageInfo");
return new ContextImpl(null, mainThread,
packageInfo, null, null, 0, null, null, Display.INVALID_DISPLAY);
}复制代码
建立ContextImpl对象并返回。
Step 26.Instrumentation.createAppContext
public Application newApplication(ClassLoader cl, String className, Context context) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
return newApplication(cl.loadClass(className), context);
}复制代码
这里主要是调用newApplication方法返回Application。
Step 28.Instrumentation.newApplication
static public Application newApplication(Class<?> clazz, Context context) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
Application app = (Application)clazz.newInstance();
app.attach(context);
return app;
}复制代码
调用class.newInstance方法建立Application，而后调用Application.attach方法，向Application中传入context。
Step 32.Application.attach
/* package */ final void attach(Context context) {
attachBaseContext(context);
mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;
}复制代码
经过ContextImpl.getImpl方法获取LoadedApk对象。
Step 34.Instrumentation.callApplicationOnCreate
public void callApplicationOnCreate(Application app) {
app.onCreate();
}复制代码
这里开始调用Application的onCreate方法。
Step 39.ActivityThread.getSystemContext
public ContextImpl getSystemContext() {
synchronized (this) {
if (mSystemContext == null) {
mSystemContext = ContextImpl.createSystemContext(this);
}
return mSystemContext;
}
}复制代码
经过ContextImpl.createSystemContext建立mSystemContext。
Step 40.ContextImpl.createSystemContext
static ContextImpl createSystemContext(ActivityThread mainThread) {
LoadedApk packageInfo = new LoadedApk(mainThread);
ContextImpl context = new ContextImpl(null, mainThread,
packageInfo, null, null, 0, null, null, Display.INVALID_DISPLAY);
context.mResources.updateConfiguration(context.mResourcesManager.getConfiguration(),
context.mResourcesManager.getDisplayMetrics());
return context;
}复制代码
建立ContextImpl而且返回。
Step 43.SystemServer.startBootstrapServices
private void startBootstrapServices() {
...
// 安装服务
Installer installer = mSystemServiceManager.startService(Installer.class);
// Activity管理服务
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
...
// 电量管理服务
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
...
// 管理LEDs和背光灯服务
mSystemServiceManager.startService(LightsService.class);
// 显示管理服务
mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);
mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
// 包管理服务
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
mFirstBoot = mPackageManagerService.isFirstBoot();
mPackageManager = mSystemContext.getPackageManager();
...
// 启动用户管理服务
mSystemServiceManager.startService(UserManagerService.LifeCycle.class);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
//初始化安装包资源的属性缓存
AttributeCache.init(mSystemContext);
// 启动系统进程的应用实例
mActivityManagerService.setSystemProcess();
// 启动传感器服务
startSensorService();
}复制代码
这里主要是启动系统引导服务。
Step 44.SystemServer.startCoreServices
private void startCoreServices() {
// 启动电池服务
mSystemServiceManager.startService(BatteryService.class);
// 启动应用统计服务
mSystemServiceManager.startService(UsageStatsService.class);
mActivityManagerService.setUsageStatsManager(
LocalServices.getService(UsageStatsManagerInternal.class));
// 启动WebView更新服务
mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class);
}复制代码
启动核心服务。
Step 45.SystemServer.startOtherServices
这里代码就不贴了，都是启动服务的代码，这里有不少服务，我简单列一下服务并说一下服务基本功能。
| 服务 | 名称 | 服务 | 名称 |
|---|---|---|---|
| SchedulingPolicyService | CameraService | ||
| TelecomLoaderService | AccountManagerService.Lifecycle | ||
| ContentService.Lifecycle | VibratorService | ||
| ConsumerIrService | AlarmManagerService | ||
| InputManagerService | WindowManagerService | ||
| VrManagerService | PersistentDataBlockService | ||
| MetricsLoggerService | IpConnectivityMetrics | ||
| PinnerService | InputMethodManagerService.Lifecycle | ||
| MountService.Lifecycle | UiModeManagerService | ||
| LockSettingsService.Lifecycle | BluetoothService | ||
| DeviceIdleController | NsdService | ||
| StatusBarManagerService | ClipboardService | ||
| NetworkManagementService | WifiService | ||
| NetworkScoreService | NetworkStatsService | ||
| NetworkPolicyManagerService | WifiNanService | ||
| WifiP2pService | TextServicesManagerService.Lifecycle | ||
| WifiScanningService | ConnectivityService | ||
| RttService | DevicePolicyManagerService.Lifecycle | ||
| UpdateLockService | RecoverySystemService | ||
| NotificationManagerService | DeviceStorageMonitorService | ||
| LocationManagerService | CountryDetectorService | ||
| SearchManagerService.Lifecycle | DropBoxManagerService | ||
| AudioService.Lifecycle | DockObserver | ||
| ThermalObserver | MidiService.Lifecycle | ||
| UsbService.Lifecycle | SerialService | ||
| HardwarePropertiesManagerService | NightDisplayService | ||
| JobSchedulerService | SoundTriggerService | ||
| BackupManagerService.Lifecycle | AppWidgetService | ||
| VoiceInteractionManagerService | GestureLauncherService | ||
| SensorNotificationService | ContextHubSystemService | ||
| DiskStatsService | SamplingProfilerService | ||
| NetworkTimeUpdateService | CommonTimeManagementService | ||
| EmergencyAffordanceService | DreamManagerService | ||
| AssetAtlasService | GraphicsStatsService | ||
| PrintManagerService | RestrictionsManagerService | ||
| MediaSessionService | HdmiControlService | ||
| TvInputManagerService | MediaResourceMonitorService | ||
| TvRemoteService | MediaRouterService | ||
| TrustManagerService | FingerprintService | ||
| ShortcutService.Lifecycle | LauncherAppsService | ||
| MediaProjectionManagerService | WearBluetoothService | ||
| WearWifiMediatorService | WearTimeService | ||
| MmsServiceBroker | RetailDemoModeService | ||
| NsdService | WallpaperManagerService.Lifecycle |
参考：
Android系统启动-SystemServer下篇
Android系统进程Zygote启动过程的源代码分析
注
原文地址：Android系统源码分析--Zygote和SystemServer启动过程
Android开发群：192508518
微信公众帐号：Code-MX
注：本文原创，转载请注明出处，多谢。
- 1. Android系统进程Zygote启动过程的源代码分析
- 2. Android SystemServer启动流程源码解析
- 3. [原]Android系统进程Zygote启动过程的源代码分析
- 4. Android Zygote启动流程源码解析
- 5. Android源码分析之SystemServer系统服务建立过程
- 6. Android源码解析之Zygote启动过程的源代码分析
- 7. 笔记：Zygote和SystemServer进程启动过程
- 8. 系统源码-1：Android 系统启动流程源码分析
- 9. Android源码分析--Android系统启动
- 10. Zygote进程启动过程源代码分析（转）
- 更多相关文章...
- • 高并发系统的分析和设计 - 红包项目实战
- • Swift 析构过程 - Swift 教程
- • Docker容器实战(七) - 容器眼光下的文件系统
- • Git五分钟教程
-
每一个你不满意的现在，都有一个你没有努力的曾经。
- 1. Android系统进程Zygote启动过程的源代码分析
- 2. Android SystemServer启动流程源码解析
- 3. [原]Android系统进程Zygote启动过程的源代码分析
- 4. Android Zygote启动流程源码解析
- 5. Android源码分析之SystemServer系统服务建立过程
- 6. Android源码解析之Zygote启动过程的源代码分析
- 7. 笔记：Zygote和SystemServer进程启动过程
- 8. 系统源码-1：Android 系统启动流程源码分析
- 9. Android源码分析--Android系统启动
- 10. Zygote进程启动过程源代码分析（转）