Android系統源碼分析--Zygote和SystemServer啓動過程
按計劃原本從這章開始寫四大組件的啓動過程的，可是看看源碼結構發現爲了說的更明白仍是先寫一點系統framework層啓動的內容，幫助理解四大組件的啓動以及管理過程。咱們知道四大組件管理是經過一些服務以及線程實現的，因此先把一些基本概念弄清楚比較好，好比AMS（ActivityManagerService）、PMS（PackageManagerService）等系統服務的做用以及調用方式，瞭解這些以後再看四大組件相對容易些，所以咱們本章先介紹系統啓動、部分系統服務的做用。java
Zygote啓動過程
Zygote是一個孕育器，Android系統全部的應用進程以及系統服務SystemServer都是有Zygote進程孕育（fork）而生的，所以Zygote在Android啓動過程當中起着決定做用。Zygote的啓動是從它的main函數開始的，所以咱們從這個函數開始分析。整個過程看下面的時序圖。android
下面咱們開始根據時序圖進行分析。git
Step 0.ZygoteInit.main緩存
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) {
...
}
}複製代碼
首先調用registerZygoteSocket方法，建立一個socket接口，用來和ActivityManagerService通信，而後調用preload方法預加載一些資源等；而後調用gcAndFinalize方法釋放一些內存；而後調用startSystemServer方法啓動SystemServer組件，而後調用runSelectLoop方法，建立一個無限循環，在socket接口上等待ActivityManagerService請求建立新的應用程序進程；最後調用closeServerSocket方法關閉上面建立的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);
}
}
}複製代碼
這個sServerSocket是經過傳入FileDescriptor（文件描述者）經過new一個來LocalServerSocket建立的。socket
Step 2.LocalServerSocket函數
public LocalServerSocket(FileDescriptor fd) throws IOException {
impl = new LocalSocketImpl(fd);
impl.listen(LISTEN_BACKLOG);
localAddress = impl.getSockAddress();
}複製代碼
在LocalServerSocket構造函數中又new了一個LocalSocketImpl，而後調用LocalSocketImpl的listen方法，最後經過getSockAddress方法獲取LocalSocketAddress對象。oop
Step 3.LocalSocketImpl源碼分析
/*package*/ LocalSocketImpl(FileDescriptor fd) throws IOException
{
this.fd = fd;
}複製代碼
這裏只是傳入了FileDescriptor（文件描述者）。
Step 5.ZygoteInit.preload
static void preload() {
...
beginIcuCachePinning();
...
preloadClasses();
...
preloadResources();
...
preloadOpenGL();
...
preloadSharedLibraries();
preloadTextResources();
...
}複製代碼
這裏主要是預加載，1.預加載ICU緩存，2.執行Zygote進程初始化，預加載一些普通類，3.預加載mResources，4.預加載OpenGL，5.預加載共享庫，6.預加載TextView的字體緩存。
Step 12.ZygoteInit.gcAndFinalize
/*package*/ static void gcAndFinalize() {
final VMRuntime runtime = VMRuntime.getRuntime();
...
System.gc();
runtime.runFinalizationSync();
System.gc();
}複製代碼
這裏主要是調用System.gc來釋放一部份內存。
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;
}複製代碼
首先Zygote會經過調用Zygote.forkSystemServer方法來建立一個新的進程來啓動SystemServer，而且返回這個進程的pid，若是pid爲0，而且有另一個Zygote則會執行waitForSecondaryZygote關閉另外的Zygote進程，而後調用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);
}
}複製代碼
首先調用closeServerSocket方法關閉socket，而後調用performSystemServerDexOpt來建立安裝鏈接InstallerConnection，最後調用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);
}複製代碼
首先調用nativeZygoteInit函數來執行一個Binder進程間通信機制初始化工做，而後就能夠在進程間進行通信了，而後執行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);
}複製代碼
這裏主要是執行一個invokeStaticMain方法來調用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);
}
}
}
}
}複製代碼
這裏經過acceptCommandPeer來建立ActivityManagerService與Socket的鏈接，而後調用ZygoteConnection.runOnce方法來建立新的應用程序。
SystemServer啓動過程
咱們從上面的Step 13 知道了SystemServer的main函數調用位置，下面咱們分析一下SystemServer的啓動過程。
在main方法中new了一個SystemServer而後調用它的run方法：
private void run() {
try {
...
// Mmmmmm... more memory!
// 清除vm內存增加上限，因爲啓動過程須要較多的虛擬機內存空間
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.
// 設置內存的可能有效使用率爲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.
// 訪問環境變量前，須要明確地指定用戶
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.
// 確保當前系統進程的binder調用，老是運行在前臺優先級(foreground priority)
BinderInternal.disableBackgroundScheduling(true);
// Increase the number of binder threads in system_server
BinderInternal.setMaxThreads(sMaxBinderThreads);
...
// 準備主線程的Looper
Looper.prepareMainLooper();
// Initialize native services.
// 加載android_servers.so庫，該庫包含的源碼在frameworks/base/services/目錄下
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.
// 初始化系統上下文
createSystemContext();
// Create the system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);
//將mSystemServiceManager添加到本地服務的成員sLocalServiceObjects
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
} finally {
...
}
// Start services.
try {
...
startBootstrapServices(); // 啓動引導服務
startCoreServices(); // 啓動核心服務
startOtherServices(); // 啓動其餘服務
} catch (Throwable ex) {
...
} finally {
...
}
...
// Loop（循環） forever.
Looper.loop();
...
}複製代碼
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);
}
}
}複製代碼
確認設備的指紋屬性。
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();
}
}複製代碼
準備main looper，這個詳細的過程咱們下一章再講，這裏先看一下流程。
Step 10.SystemServer.performPendingShutdown
private void performPendingShutdown() {
final String shutdownAction = SystemProperties.get(
ShutdownThread.SHUTDOWN_ACTION_PROPERTY, "");
if (shutdownAction != null && shutdownAction.length() > 0) {
// 是否重啓
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);
}
}複製代碼
這裏主要是經過關機的action來判斷是否重啓或者關機。
Step 13.SystemServer.createSystemContext
private void createSystemContext() {
// 初始化ActivityThread，並設置默認主題
ActivityThread activityThread = ActivityThread.systemMain();
mSystemContext = activityThread.getSystemContext();
mSystemContext.setTheme(DEFAULT_SYSTEM_THEME);
}複製代碼
首先調用ActivityThread.systemMain方法建立ActivityThread對象而後獲取mSystemContext，而且設置默認系統主題。
Step 15.ActivityThread.systemMain
public static ActivityThread systemMain() {
...
ActivityThread thread = new ActivityThread();
thread.attach(true);
return thread;
}複製代碼
建立ActivityThread對象，並調用attach方法。
Step 17.ResourcesManager.getInstance
public static ResourcesManager getInstance() {
synchronized (ResourcesManager.class) {
if (sResourcesManager == null) {
sResourcesManager = new ResourcesManager();
}
return sResourcesManager;
}複製代碼
單例模式建立ResourcesManager對象而且返回。
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) {
...
}
}
...
}複製代碼
由於參數傳入的是true，代表是系統的線程，因此執行else裏面的內容，首先建立Instrumentation，而後調用ContextImpl.createAppContext方法建立ContextImpl，而後經過調用LoadedApk.makeApplication方法建立Application，而後調用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);
}複製代碼
經過new ContextImpl來建立ContextImpl對象。
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;
}複製代碼
經過ContextImpl.createAppContext方法建立ContextImpl對象，而後調用mActivityThread.mInstrumentation.newApplication方法建立Application對象，而後調用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);
}複製代碼
建立ContextImpl對象並返回。
Step 26.Instrumentation.createAppContext
public Application newApplication(ClassLoader cl, String className, Context context) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
return newApplication(cl.loadClass(className), context);
}複製代碼
這裏主要是調用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;
}複製代碼
調用class.newInstance方法建立Application，而後調用Application.attach方法，向Application中傳入context。
Step 32.Application.attach
/* package */ final void attach(Context context) {
attachBaseContext(context);
mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;
}複製代碼
經過ContextImpl.getImpl方法獲取LoadedApk對象。
Step 34.Instrumentation.callApplicationOnCreate
public void callApplicationOnCreate(Application app) {
app.onCreate();
}複製代碼
這裏開始調用Application的onCreate方法。
Step 39.ActivityThread.getSystemContext
public ContextImpl getSystemContext() {
synchronized (this) {
if (mSystemContext == null) {
mSystemContext = ContextImpl.createSystemContext(this);
}
return mSystemContext;
}
}複製代碼
經過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;
}複製代碼
建立ContextImpl而且返回。
Step 43.SystemServer.startBootstrapServices
private void startBootstrapServices() {
...
// 安裝服務
Installer installer = mSystemServiceManager.startService(Installer.class);
// Activity管理服務
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
...
// 電量管理服務
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
...
// 管理LEDs和背光燈服務
mSystemServiceManager.startService(LightsService.class);
// 顯示管理服務
mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);
mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
// 包管理服務
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
mFirstBoot = mPackageManagerService.isFirstBoot();
mPackageManager = mSystemContext.getPackageManager();
...
// 啓動用戶管理服務
mSystemServiceManager.startService(UserManagerService.LifeCycle.class);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
//初始化安裝包資源的屬性緩存
AttributeCache.init(mSystemContext);
// 啓動系統進程的應用實例
mActivityManagerService.setSystemProcess();
// 啓動傳感器服務
startSensorService();
}複製代碼
這裏主要是啓動系統引導服務。
Step 44.SystemServer.startCoreServices
private void startCoreServices() {
// 啓動電池服務
mSystemServiceManager.startService(BatteryService.class);
// 啓動應用統計服務
mSystemServiceManager.startService(UsageStatsService.class);
mActivityManagerService.setUsageStatsManager(
LocalServices.getService(UsageStatsManagerInternal.class));
// 啓動WebView更新服務
mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class);
}複製代碼
啓動核心服務。
Step 45.SystemServer.startOtherServices
這裏代碼就不貼了，都是啓動服務的代碼，這裏有不少服務，我簡單列一下服務並說一下服務基本功能。
| 服務 | 名稱 | 服務 | 名稱 |
|---|---|---|---|
| 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 |
參考：
Android系統啓動-SystemServer下篇
Android系統進程Zygote啓動過程的源代碼分析
注
原文地址：Android系統源碼分析--Zygote和SystemServer啓動過程
Android開發羣：192508518
微信公衆帳號：Code-MX
注：本文原創，轉載請註明出處，多謝。
- 1. Android系統進程Zygote啓動過程的源代碼分析
- 2. Android SystemServer啓動流程源碼解析
- 3. [原]Android系統進程Zygote啓動過程的源代碼分析
- 4. Android Zygote啓動流程源碼解析
- 5. Android源碼分析之SystemServer系統服務建立過程
- 6. Android源碼解析之Zygote啓動過程的源代碼分析
- 7. 筆記：Zygote和SystemServer進程啓動過程
- 8. 系統源碼-1：Android 系統啓動流程源碼分析
- 9. Android源碼分析--Android系統啓動
- 10. Zygote進程啓動過程源代碼分析（轉）
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- 1. Android系統進程Zygote啓動過程的源代碼分析
- 2. Android SystemServer啓動流程源碼解析
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- 4. Android Zygote啓動流程源碼解析
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