首先我们要知道，主要系统服务都是在 SystemServer 启动的，蓝牙也是如此：
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,
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。
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