Android藍牙服務啟動流程分析探索
首先我們要知道,主要系統服務都是在 SystemServer 啟動的,藍牙也是如此:
1、SystemServer
源碼路徑:/frameworks/base/services/java/com/android/server/SystemServer.java
private void startOtherServices(@NonNull TimingsTraceAndSlog t) { if (mFactoryTestMode == FactoryTest.FACTORY_TEST_LOW_LEVEL) { Slog.i(TAG, "No Bluetooth Service (factory test)"); } else if (!context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH)) { Slog.i(TAG, "No Bluetooth Service (Bluetooth Hardware Not Present)"); } else { t.traceBegin("StartBluetoothService"); mSystemServiceManager.startService(BluetoothService.class); t.traceEnd(); } }
SystemServer 在啟動其他服務的方法里,啟動了 BluetoothService。
2、BluetoothService
class BluetoothService extends SystemService { private BluetoothManagerService mBluetoothManagerService; public BluetoothService(Context context) { super(context); //創(chuàng)建BluetoothManagerService的實例 mBluetoothManagerService = new BluetoothManagerService(context); } ...... @Override public void onBootPhase(int phase) { if (phase == SystemService.PHASE_SYSTEM_SERVICES_READY) { //將BluetoothManagerService實例發(fā)布到系統中,這樣就可以Context根據BT的service名去獲取它的Binder代理操作API了 publishBinderService(BluetoothAdapter.BLUETOOTH_MANAGER_SERVICE, mBluetoothManagerService); } else if (phase == SystemService.PHASE_ACTIVITY_MANAGER_READY) { //此時系統應該啟動到一個比較晚的階段了,可以使用AMS去Bind需要的Service了 mBluetoothManagerService.handleOnBootPhase(); } } ...... }
可以看到,真正獲取的服務是BluetoothManagerService 而非 BluetoothService??梢酝ㄟ^ ServiceManager.getService(BLUETOOTH_MANAGER _SERVICE) 獲取藍牙服務。
onBootPhase(int):這個函數應該是 systemserver 在啟動的時候會多次調用,參數代表當前啟動進行到了什么階段,用戶定義的 service 針對各個階段需要做怎樣的處理或者是不做任何處理。
3、BluetoothManagerService
BluetoothManagerService(Context context) { //創(chuàng)建內部處理msg的handler mHandler = new BluetoothHandler(IoThread.get().getLooper()); mContext = context; ...... //false表示此次enable需要觸發(fā)auto connect device和保存狀態(tài),BluetoothAdapter::enableNoAutoConnect()可以改變此狀態(tài) mQuietEnableExternal = false; mEnableExternal = false; ...... IntentFilter filter = new IntentFilter(); //監(jiān)聽App通過接口修改BT 名稱的廣播 filter.addAction(BluetoothAdapter.ACTION_LOCAL_NAME_CHANGED); //監(jiān)聽bt地址改變的廣播 filter.addAction(BluetoothAdapter.ACTION_BLUETOOTH_ADDRESS_CHANGED); //監(jiān)聽當前設置需要restore回上一次設置的廣播,此時需要重新保存name和addr為上一次的信息 filter.addAction(Intent.ACTION_SETTING_RESTORED); filter.setPriority(IntentFilter.SYSTEM_HIGH_PRIORITY); mContext.registerReceiver(mReceiver, filter); //從數據庫中加載本機Bt的local name和address loadStoredNameAndAddress(); //查看上一次關機時,BT是否為enable狀態(tài);如果是,這次開機也需要enable BT if (isBluetoothPersistedStateOn()) { if (DBG) { Slog.d(TAG, "Startup: Bluetooth persisted state is ON."); } mEnableExternal = true;//表明開機過程中需要enable BT } }
在服務啟動到一定階段就會回調到 SystemService 的 onBootPhase(int) 方法,即 2 中的該方法,然后調用 BMS 中的 handleOnBootPhase() 方法。
public void handleOnBootPhase() { ...... final boolean isSafeMode = mContext.getPackageManager().isSafeMode(); if (mEnableExternal && isBluetoothPersistedStateOnBluetooth() && && !isSafeMode) { sendEnableMsg(mQuietEnableExternal/*默認false,表示此次enable需要自動連接device/保存enable狀態(tài)*/, BluetoothProtoEnums.ENABLE_DISABLE_REASON_SYSTEM_BOOT, mContext.getPackageName()); } else if (!isNameAndAddressSet()) { Message getMsg = mHandler.obtainMessage(MESSAGE_GET_NAME_AND_ADDRESS); mHandler.sendMessage(getMsg); } ...... }
handleOnBootPhase()的內容比較單一,根據一些flag判斷是否需要enable BT;而enable藍牙這里是通過觸發(fā)send msg實現。
private void sendEnableMsg(boolean quietMode, int reason, String packageName) { //發(fā)送MESSAGE_ENABLE msg mHandler.sendMessage(mHandler.obtainMessage(MESSAGE_ENABLE, quietMode ? 1 : 0, 0)); addActiveLog(reason, packageName, true); mLastEnabledTime = SystemClock.elapsedRealtime(); } case MESSAGE_ENABLE: int quietEnable = msg.arg1; mQuietEnable = (quietEnable == 1);//此時為false //mBluetooth是后面綁定Bt apk中AdapterService時拿到的Binder代理對象;用以把操作bypass到BT核心框架中 if (mBluetooth == null) { handleEnable(mQuietEnable); } else {//如果mBluetooth不是null,說明之前已經啟動過了;此時是Restart flow,以MESSAGE_RESTART_BLUETOOTH_SERVICE觸發(fā) mWaitForEnableRetry = 0; Message enableDelayedMsg = mHandler.obtainMessage(MESSAGE_HANDLE_ENABLE_DELAYED); mHandler.sendMessageDelayed(enableDelayedMsg, ENABLE_DISABLE_DELAY_MS); } break;
handleEnable() 去 Bind AdapterService 拿到它的Binder句柄。同樣的在調用 BluetoothManagerService 中的 enable()、disable()等方法時,也是調到 handleEnable() 方法,從而最終調用 AdapterService 中的 enable()、disable() 方法。
private void handleEnable(boolean quietMode) { mQuietEnable = quietMode; try { mBluetoothLock.writeLock().lock(); if ((mBluetooth == null) && (!mBinding)) { //Start bind timeout and bind Message timeoutMsg = mHandler.obtainMessage(MESSAGE_TIMEOUT_BIND); mHandler.sendMessageDelayed(timeoutMsg, TIMEOUT_BIND_MS); Intent i = new Intent(IBluetooth.class.getName()); if (!doBind(i, mConnection, Context.BIND_AUTO_CREATE | Context.BIND_IMPORTANT, UserHandle.CURRENT)) { mHandler.removeMessages(MESSAGE_TIMEOUT_BIND); } else { mBinding = true; } } } finally { mBluetoothLock.writeLock().unlock(); } }
然后我們看一下 doBind() 方法中的 mConnection 參數:
private BluetoothServiceConnection mConnection = new BluetoothServiceConnection(); private class BluetoothServiceConnection implements ServiceConnection { public void onServiceConnected(ComponentName componentName, IBinder service) { String name = componentName.getClassName(); Message msg = mHandler.obtainMessage(MESSAGE_BLUETOOTH_SERVICE_CONNECTED); if (name.equals("com.android.bluetooth.btservice.AdapterService")) { msg.arg1 = SERVICE_IBLUETOOTH; } else if (name.equals("com.android.bluetooth.gatt.GattService")) { msg.arg1 = SERVICE_IBLUETOOTHGATT; } else { Slog.e(TAG, "Unknown service connected: " + name); return; } msg.obj = service; mHandler.sendMessage(msg); } public void onServiceDisconnected(ComponentName componentName) { // Called if we unexpectedly disconnect. String name = componentName.getClassName(); Message msg = mHandler.obtainMessage(MESSAGE_BLUETOOTH_SERVICE_DISCONNECTED); if (name.equals("com.android.bluetooth.btservice.AdapterService")) { msg.arg1 = SERVICE_IBLUETOOTH; } else if (name.equals("com.android.bluetooth.gatt.GattService")) { msg.arg1 = SERVICE_IBLUETOOTHGATT; } else { Slog.e(TAG, "Unknown service disconnected: " + name); return; } mHandler.sendMessage(msg); } }
拿到 AdapterService 服務后,發(fā)送MESSAGE_BLUETOOTH_SERVICE_CONNECTED消息且 arg1 = SERVICE_IBLUETOOTH。
case MESSAGE_BLUETOOTH_SERVICE_CONNECTED: { IBinder service = (IBinder) msg.obj; try { mBluetoothLock.writeLock().lock(); mBinding = false; mBluetoothBinder = service; mBluetooth = IBluetooth.Stub.asInterface(Binder.allowBlocking(service)); //Register callback object try { mBluetooth.registerCallback(mBluetoothCallback, mContext.getAttributionSource()); } catch (RemoteException re) { Slog.e(TAG, "Unable to register BluetoothCallback", re); } //Inform BluetoothAdapter instances that service is up sendBluetoothServiceUpCallback(); //Do enable request try { if (!mBluetooth.enable(mQuietEnable, mContext.getAttributionSource())) { Slog.e(TAG, "IBluetooth.enable() returned false"); } } catch (RemoteException e) { Slog.e(TAG, "Unable to call enable()", e); } } finally { mBluetoothLock.writeLock().unlock(); } if (!mEnable) { waitForState(Set.of(BluetoothAdapter.STATE_ON)); handleDisable(); waitForState(Set.of(BluetoothAdapter.STATE_OFF, BluetoothAdapter.STATE_TURNING_ON, BluetoothAdapter.STATE_TURNING_OFF, BluetoothAdapter.STATE_BLE_TURNING_ON, BluetoothAdapter.STATE_BLE_ON, BluetoothAdapter.STATE_BLE_TURNING_OFF)); } }
主要操作:
1、拿到 bind 服務的 onBinder() 句柄,并轉成 IBluetooth 類型
2、通過 IBluetooth 類型的 obj,調用 enable() 接口,將 flow 轉到 AdapterService 中,做一些初始化、并向 stack 下 enable 藍牙的 cmd
至此,enable 藍牙的 flow 就從 BluetoothManagerService 轉到 AdapterService 中了;實際上,通過 BluetoothAdapter 下來的大部分 API 調用最終都是調用到 AdapterService,再通過它下cmd 給 stack。
兩個常見到的flag:
mEnable:用來標記系統運行時,藍牙狀態(tài)的變化,它有些時候跟 mEnableExternal 值一致。但如果藍牙的狀態(tài)是因為某些原因,如 stack 崩潰,導致藍牙需要重啟,重新啟動時,需要靠這個 flag 來標記這種 case 的 enable/disable 狀態(tài)。
mEnableExternal:它主要是記錄通過用戶手動操作導致的BT使能狀態(tài),如通過藍牙功能按鈕來 enable/disable 藍牙。
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