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();
    }
}

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();
        }
    }
    ......
}

    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
        }
    }

    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);
        }
        ......
    }

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;

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();
    }
}

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);
    }
}

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));
    }
}