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Android藍(lán)牙服務(wù)啟動(dòng)流程分析探索_Android

作者：c小旭 ? 更新時(shí)間： 2023-03-16 編程語(yǔ)言

首先我們要知道，主要系統(tǒng)服務(wù)都是在 SystemServer 啟動(dòng)的，藍(lán)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(dòng)其他服務(wù)的方法里，啟動(dòng)了 BluetoothService。

2、BluetoothService

class BluetoothService extends SystemService {
    private BluetoothManagerService mBluetoothManagerService;
    public BluetoothService(Context context) {
        super(context);
        //創(chuàng)建BluetoothManagerService的實(shí)例
        mBluetoothManagerService = new BluetoothManagerService(context);
    }
    ......
    @Override
    public void onBootPhase(int phase) {
        if (phase == SystemService.PHASE_SYSTEM_SERVICES_READY) {
            //將BluetoothManagerService實(shí)例發(fā)布到系統(tǒng)中，這樣就可以Context根據(jù)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(shí)系統(tǒng)應(yīng)該啟動(dòng)到一個(gè)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(wù)是BluetoothManagerService 而非 BluetoothService。可以通過 ServiceManager.getService(BLUETOOTH_MANAGER _SERVICE) 獲取藍(lán)牙服務(wù)。

onBootPhase(int)：這個(gè)函數(shù)應(yīng)該是 systemserver 在啟動(dòng)的時(shí)候會(huì)多次調(diào)用，參數(shù)代表當(dāng)前啟動(dòng)進(jìn)行到了什么階段，用戶定義的 service 針對(duì)各個(gè)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(nèi)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(dāng)前設(shè)置需要restore回上一次設(shè)置的廣播,此時(shí)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(shù)據(jù)庫(kù)中加載本機(jī)Bt的local name和address
        loadStoredNameAndAddress();
        //查看上一次關(guān)機(jī)時(shí),BT是否為enable狀態(tài);如果是,這次開機(jī)也需要enable BT
        if (isBluetoothPersistedStateOn()) {
            if (DBG) {
                Slog.d(TAG, "Startup: Bluetooth persisted state is ON.");
            }
            mEnableExternal = true;//表明開機(jī)過程中需要enable BT
        }
    }

在服務(wù)啟動(dòng)到一定階段就會(huì)回調(diào)到 SystemService 的 onBootPhase(int) 方法，即 2 中的該方法，然后調(diào)用 BMS 中的 handleOnBootPhase() 方法。

    public void handleOnBootPhase() {   
        ......
        final boolean isSafeMode = mContext.getPackageManager().isSafeMode();
        if (mEnableExternal && isBluetoothPersistedStateOnBluetooth() && && !isSafeMode) {
            sendEnableMsg(mQuietEnableExternal/*默認(rèn)false,表示此次enable需要自動(dòng)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(nèi)容比較單一，根據(jù)一些flag判斷是否需要enable BT；而enable藍(lán)牙這里是通過觸發(fā)send msg實(shí)現(xiàn)。

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(shí)為false
    //mBluetooth是后面綁定Bt apk中AdapterService時(shí)拿到的Binder代理對(duì)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(jīng)啟動(dòng)過了;此時(shí)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(diào)用 BluetoothManagerService 中的 enable()、disable()等方法時(shí)，也是調(diào)到 handleEnable() 方法，從而最終調(diào)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(shù)：

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(wù)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(wù)的 onBinder() 句柄，并轉(zhuǎn)成 IBluetooth 類型

2、通過 IBluetooth 類型的 obj，調(diào)用 enable() 接口，將 flow 轉(zhuǎn)到 AdapterService 中，做一些初始化、并向 stack 下 enable 藍(lán)牙的 cmd

至此，enable 藍(lán)牙的 flow 就從 BluetoothManagerService 轉(zhuǎn)到 AdapterService 中了；實(shí)際上，通過 BluetoothAdapter 下來的大部分 API 調(diào)用最終都是調(diào)用到 AdapterService，再通過它下cmd 給 stack。

兩個(gè)常見到的flag：

mEnable：用來標(biāo)記系統(tǒng)運(yùn)行時(shí)，藍(lán)牙狀態(tài)的變化，它有些時(shí)候跟 mEnableExternal 值一致。但如果藍(lán)牙的狀態(tài)是因?yàn)槟承┰颍?stack 崩潰，導(dǎo)致藍(lán)牙需要重啟，重新啟動(dòng)時(shí)，需要靠這個(gè) flag 來標(biāo)記這種 case 的 enable/disable 狀態(tài)。

mEnableExternal：它主要是記錄通過用戶手動(dòng)操作導(dǎo)致的BT使能狀態(tài)，如通過藍(lán)牙功能按鈕來 enable/disable 藍(lán)牙。

原文鏈接：https://blog.csdn.net/c19344881x/article/details/128718529

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