Android蓝牙服务启动流程分析探索

1、SystemServer

源码路径：/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 在启动其他服务的方法里，启动了 BluetoothService。

2、BluetoothService

class BluetoothService extends SystemService {
 private BluetoothManagerService mBluetoothManagerService;
 public BluetoothService(Context context) {
 super(context);
 //创建BluetoothManagerService的实例
 mBluetoothManagerService = new BluetoothManagerService(context);
 }
 ......
 @Override
 public void onBootPhase(int phase) {
 if (phase == SystemService.PHASE_SYSTEM_SERVICES_READY) {
 //将BluetoothManagerService实例发布到系统中，这样就可以Context根据BT的service名去获取它的Binder代理操作API了
 publishBinderService(BluetoothAdapter.BLUETOOTH_MANAGER_SERVICE,
 mBluetoothManagerService);
 } else if (phase == SystemService.PHASE_ACTIVITY_MANAGER_READY) {
 //此时系统应该启动到一个比较晚的阶段了，可以使用AMS去Bind需要的Service了
 mBluetoothManagerService.handleOnBootPhase();
 }
 }
 ......
}

可以看到，真正获取的服务是BluetoothManagerService 而非 BluetoothService。可以通过 ServiceManager.getService(BLUETOOTH_MANAGER _SERVICE) 获取蓝牙服务。

onBootPhase(int)：这个函数应该是 systemserver 在启动的时候会多次调用，参数代表当前启动进行到了什么阶段，用户定义的 service 针对各个阶段需要做怎样的处理或者是不做任何处理。

3、BluetoothManagerService

BluetoothManagerService(Context context) {
 //创建内部处理msg的handler
 mHandler = new BluetoothHandler(IoThread.get().getLooper());
 mContext = context;
 ......
 //false表示此次enable需要触发auto connect device和保存状态,BluetoothAdapter::enableNoAutoConnect()可以改变此状态
 mQuietEnableExternal = false;
 mEnableExternal = false;
 ......
 IntentFilter filter = new IntentFilter();
 //监听App通过接口修改BT 名称的广播
 filter.addAction(BluetoothAdapter.ACTION_LOCAL_NAME_CHANGED);
 //监听bt地址改变的广播
 filter.addAction(BluetoothAdapter.ACTION_BLUETOOTH_ADDRESS_CHANGED);
 //监听当前设置需要restore回上一次设置的广播,此时需要重新保存name和addr为上一次的信息
 filter.addAction(Intent.ACTION_SETTING_RESTORED);
 filter.setPriority(IntentFilter.SYSTEM_HIGH_PRIORITY);
 mContext.registerReceiver(mReceiver, filter);
 //从数据库中加载本机Bt的local name和address
 loadStoredNameAndAddress();
 //查看上一次关机时,BT是否为enable状态;如果是,这次开机也需要enable BT
 if (isBluetoothPersistedStateOn()) {
 if (DBG) {
 Slog.d(TAG, "Startup: Bluetooth persisted state is ON.");
 }
 mEnableExternal = true;//表明开机过程中需要enable BT
 }
 }

在服务启动到一定阶段就会回调到 SystemService 的 onBootPhase(int) 方法，即 2 中的该方法，然后调用 BMS 中的 handleOnBootPhase() 方法。

public void handleOnBootPhase() { 
 ......
 final boolean isSafeMode = mContext.getPackageManager().isSafeMode();
 if (mEnableExternal && isBluetoothPersistedStateOnBluetooth() && && !isSafeMode) {
 sendEnableMsg(mQuietEnableExternal/*默认false,表示此次enable需要自动连接device/保存enable状态*/,
 BluetoothProtoEnums.ENABLE_DISABLE_REASON_SYSTEM_BOOT,
 mContext.getPackageName());
 } else if (!isNameAndAddressSet()) {
 Message getMsg = mHandler.obtainMessage(MESSAGE_GET_NAME_AND_ADDRESS);
 mHandler.sendMessage(getMsg);
 }
 ......
 }

handleOnBootPhase()的内容比较单一，根据一些flag判断是否需要enable BT；而enable蓝牙这里是通过触发send msg实现。

private void sendEnableMsg(boolean quietMode, int reason, String packageName) {
 //发送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);//此时为false
 //mBluetooth是后面绑定Bt apk中AdapterService时拿到的Binder代理对象;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,说明之前已经启动过了;此时是Restart flow,以MESSAGE_RESTART_BLUETOOTH_SERVICE触发
 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。同样的在调用 BluetoothManagerService 中的 enable()、disable()等方法时，也是调到 handleEnable() 方法，从而最终调用 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();
 }
}

然后我们看一下 doBind() 方法中的 mConnection 参数：

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 服务后，发送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 服务的 onBinder() 句柄，并转成 IBluetooth 类型

2、通过 IBluetooth 类型的 obj，调用 enable() 接口，将 flow 转到 AdapterService 中，做一些初始化、并向 stack 下 enable 蓝牙的 cmd

至此，enable 蓝牙的 flow 就从 BluetoothManagerService 转到 AdapterService 中了；实际上，通过 BluetoothAdapter 下来的大部分 API 调用最终都是调用到 AdapterService，再通过它下cmd 给 stack。

两个常见到的flag：

mEnable：用来标记系统运行时，蓝牙状态的变化，它有些时候跟 mEnableExternal 值一致。但如果蓝牙的状态是因为某些原因，如 stack 崩溃，导致蓝牙需要重启，重新启动时，需要靠这个 flag 来标记这种 case 的 enable/disable 状态。

mEnableExternal：它主要是记录通过用户手动操作导致的BT使能状态，如通过蓝牙功能按钮来 enable/disable 蓝牙。

目录

1、SystemServer

2、BluetoothService

3、BluetoothManagerService

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