认识Android的ServiceManager.doc

認識Android的天字第1號核心服務：ServiceManager 1. 認識ServiceManager模組ServiceManager是Android平台裡的一個基本模組。在Android系統啟動過程中，它就會被登錄到Binder Kernel裡，成為天字第一號的可提供遠距服務之模組。2. 在下層的C/C+類別，何處使用到ServiceManager模組呢? 使用C/C+撰寫Android的底層系統服務(System Service)模組時，經常需要使用到ServiceManager(天字第一號服務模組)的服務。此時，你可以透過defaultServiceManager()函數來取得ServiceManager模組的IServiceManager介面之指標。例如，在CameraService.cpp程式裡的instantiate()函數，其內容如下：/ -/ CameraService.cppvoid CameraService:instantiate() defaultServiceManager()-addService( String16(media.camera), new CameraService();/- 它使用了defaultServiceManager()函數來取得ServiceManager模組，然後呼叫其IServiceManager介面裡的addService()函數來將自己物件(即CameraService類別之物件)傳給ServiceManager模組，請它登錄到Binder Kernel裡，成為一個可提供遠距服務之模組(即CameraService模組)。3. 在上層的Java類別，何處使用到ServiceManager模組呢?在Java層有個ServiceManager類別。它偍供了一些函數讓其它Java類別使用。例如，ActivityManagerService.java類別裡的指令：/ -/ ActivityManagerService.javapublic static void setSystemProcess() try ActivityManagerService m = mSelf; ServiceManager.addService(activity, m); ServiceManager.addService(meminfo, new MemBinder(m); if (MONITOR_CPU_USAGE) ServiceManager.addService(cpuinfo, new CpuBinder(m); ServiceManager.addService(activity.broadcasts, new BroadcastsBinder(m); ServiceManager.addService(activity.services, new ServicesBinder(m); ServiceManager.addService(activity.senders,new SendersBinder(m); ServiceManager.addService(viders, new ProvidersBinder(m); ServiceManager.addService(permission, new PermissionController(m); ApplicationInfo info = mSelf.mContext.getPackageManager().getApplicationInfo( android, PackageManager.GET_SHARED_LIBRARY_FILES);synchronized (mSelf) ProcessRecord app = mSelf.newProcessRecordLocked( mSystemThread.getApplicationThread(), info, cessName); app.persistent = true; app.pid = Process.myPid(); app.maxAdj = SYSTEM_ADJ; mSelf.mProcessNames.put(cessName, .uid, app); synchronized (mSelf.mPidsSelfLocked) mSelf.mPidsSelfLocked.put(app.pid, app); mSelf.updateLRUListLocked(app, true); catch (PackageManager.NameNotFoundException e) throw new RuntimeException( Unable to find android system package, e); /-其中的： ActivityManagerService m = mSelf; ServiceManager.addService(activity, m);即是呼叫ServiceManager類別的addService()函數，將自己(就是ActivityManagerService)登錄到請它登錄到Binder Kernel裡，成為一個可提供遠距服務之模組(即ActivityManagerService模組)。 Java指令：ServiceManager.addService(.); 相當於 C+的指令：defaultServiceManager()-addService(.);4. ServiceManager模組如何支持C+類別 在C+層的defaultServiceManager()函數，會轉而呼叫ProcessState類別的getContextObject()函數來取得登錄於Binder Kernel裡的ServiceManager模組的介面。如下：sp defaultServiceManager() /. DefaultServiceManager = interface_cast( ProcessState:self()-getContextObject(NULL); return gDefaultServiceManager; 5. ServiceManager模組如何支持Java類別 在Java層的ServiceManager類別，它的getIServiceManager()會轉而呼叫JNI的BinderInternal.getContextObject()函數來取得登錄於Binder Kernel裡的ServiceManager模組的介面。如下： private static IServiceManager getIServiceManager() / sServiceManager = ServiceManagerNative.asInterface(BinderInternal.getContextObject(); return sServiceManager; 圖示如下：呼叫BinderInternal.getContextObject()來建立BinderProxy物件。 private static IServiceManager getIServiceManager() / sServiceManager = ServiceManagerNative.asInterface(BinderInternal.getContextObject(); return sServiceManager; Java指令：ServiceManager.getIServiceManager(.); 相當於 C+的指令：defaultServiceManager();於是，ServiceManager.java類別裡的getService()和addService()呼叫到上述的getIServiceManager()函數，如下： public static IBinder getService(String name) try IBinder service = sCache.get(name); if (service != null) return service; else return getIServiceManager().getService(name); catch (RemoteException e) Log.e(TAG, error in getService, e); retu