Bluetooth initialization - enable in Settings & System_server process

1. Overview

Bluetooth.png

蓝牙初始化框图如上：

1. 蓝牙处于关闭状态时，进程 com.android.bluetooth 不存在。
2. 以设置打开蓝牙为例，蓝牙初始化（即 enable）的流程是 com.android.settings（设置进程） ----> system_server（系统服务进程）----> com.android.bluetooth（蓝牙进程）
3. 蓝牙进程启动之后，设置应用将直接与蓝牙进程通信，无需再经过系统服务进程。

2. Settings Process - 触发开启蓝牙

frameworks/base/core/java/android/bluetooth/BluetoothAdapter.java

    public boolean enable() {
......
        try {
            return mManagerService.enable(ActivityThread.currentPackageName());
        } catch (RemoteException e) {
            Log.e(TAG, "", e);
        }
        return false;
    }

3. System_server Process

3.1 启动蓝牙进程

frameworks/base/services/core/java/com/android/server/BluetoothManagerService.java

    public boolean enable(String packageName) throws RemoteException {
......
        synchronized (mReceiver) {
......
            sendEnableMsg(false,
                    BluetoothProtoEnums.ENABLE_DISABLE_REASON_APPLICATION_REQUEST, packageName);
        }
        return true;
    }

此处传递的 quietMode = false；

    private void sendEnableMsg(boolean quietMode, int reason, String packageName) {
        mHandler.sendMessage(mHandler.obtainMessage(MESSAGE_ENABLE, quietMode ? 1 : 0, 0));
......
    }

    private class BluetoothHandler extends Handler {
......
        @Override
        public void handleMessage(Message msg) {
                case MESSAGE_ENABLE:
......
                    mQuietEnable = (msg.arg1 == 1);  // mQuietEnable = false;
                    if (mBluetooth == null) {
                        handleEnable(mQuietEnable);
                    } 
......
                    break;

首次开启时，由于 com.android.bluetooth 还未启动，因此 mBluetooth == null，故会执行绑定服务的操作。

    private void handleEnable(boolean quietMode) {
        mQuietEnable = quietMode; // false

        try {
            if ((mBluetooth == null) && (!mBinding)) {
......
                Intent i = new Intent(IBluetooth.class.getName());
                if (!doBind(i, mConnection, 
                        Context.BIND_AUTO_CREATE | Context.BIND_IMPORTANT,
                        UserHandle.CURRENT)) {
                } else {
                    mBinding = true;
                }
            } else if (mBluetooth != null) {
......
            }
        }
    }

    boolean doBind(Intent intent, ServiceConnection conn, int flags, UserHandle user) {
        ComponentName comp = intent.resolveSystemService(mContext.getPackageManager(), 0);
        intent.setComponent(comp);
        if (comp == null || !mContext.bindServiceAsUser(intent, conn, flags, user)) {
            return false;
        }
        return true;
    }

绑定的是 IBluetooth 这个服务，由以下配置信息可知，绑定的是 AdapterService.java，该绑定过程会启动 com.android.bluetooth 进程。
packages/apps/Bluetooth/AndroidManifest.xml

蓝牙进程的启动过程由 蓝牙进程初始化 来分析，此文继续分析服务被绑定成功后的回调。

3.2 绑定 AdapterService 成功后的回调

frameworks/base/services/core/java/com/android/server/BluetoothManagerService.java

    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;
......
            }
            msg.obj = service;
            mHandler.sendMessage(msg);
        }
......
    }



    private BluetoothServiceConnection mConnection = new BluetoothServiceConnection();

以上源码主要是创建了 MESSAGE_BLUETOOTH_SERVICE_CONNECTED 消息，下面开始处理该消息。

    private class BluetoothHandler extends Handler {
......
        @Override
        public void handleMessage(Message msg) {
                case MESSAGE_BLUETOOTH_SERVICE_CONNECTED: {

                    IBinder service = (IBinder) msg.obj;
                    try {
                        mBluetoothLock.writeLock().lock();
                        if (msg.arg1 == SERVICE_IBLUETOOTHGATT) {
......
                            return;
                        } // else must be SERVICE_IBLUETOOTH
......
                        mBinding = false;
                        mBluetoothBinder = service;
                        // 0. 获取蓝牙进程蓝牙适配器服务的代理对象
                        mBluetooth = IBluetooth.Stub.asInterface(Binder.allowBlocking(service));
......
                        // 1. 向蓝牙进程注册回调函数，以达到双向通信的目的
                        try {
                            mBluetooth.registerCallback(mBluetoothCallback);
                        } catch (RemoteException re) {
                            Slog.e(TAG, "Unable to register BluetoothCallback", re);
                        }
                        // 2. Inform BluetoothAdapter instances that service is up
                        sendBluetoothServiceUpCallback();

                        // 3. Do enable request
                        try {
                            if (!mBluetooth.enable(mQuietEnable)) {
                                Slog.e(TAG, "IBluetooth.enable() returned false");
                            }
                        } catch (RemoteException e) {
                            Slog.e(TAG, "Unable to call enable()", e);
                        }

处理 MESSAGE_BLUETOOTH_SERVICE_CONNECTED 消息，从源码可知：
首先，获取并保存蓝牙进程入口的代理对象：mBluetooth；
其次，

1. 向蓝牙进程注册回调，用于蓝牙进程向系统服务进程发送消息；
2. 执行应用层注册到系统服务进程的回调，向已注册的应用进程提供 蓝牙进程入口的代理对象；
3. 向蓝牙进程发起执行 enable 操作的请求。

3.2.1 registerCallback

3.2.1.1 Register Flow

packages/apps/Bluetooth/src/com/android/bluetooth/btservice/AdapterService.java
AdapterService 存储该回调对象，在合适的时候触发回调。

public class AdapterService extends Service {

    private RemoteCallbackList mCallbacks = 
            new RemoteCallbackList();

    public static class AdapterServiceBinder extends IBluetooth.Stub {

        public void registerCallback(IBluetoothCallback callback) {
            AdapterService service = getService();
......
            service.mCallbacks.register(callback);
        }
    }

3.2.1.2 Callback Implementation

frameworks/base/services/core/java/com/android/server/BluetoothManagerService.java

    private final IBluetoothCallback mBluetoothCallback = new IBluetoothCallback.Stub() {
        @Override
        public void onBluetoothStateChange(int prevState, int newState) throws RemoteException {
            Message msg =
                    mHandler.obtainMessage(MESSAGE_BLUETOOTH_STATE_CHANGE, prevState, newState);
            mHandler.sendMessage(msg);
        }
    };

从以上源码可知，蓝牙进程调用该回调以通知系统服务进程蓝牙的状态变化信息。

    private class BluetoothHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MESSAGE_BLUETOOTH_STATE_CHANGE: {
                    int prevState = msg.arg1;
                    int newState = msg.arg2;
                    mState = newState;
                    bluetoothStateChangeHandler(prevState, newState);
  ......
                    break;
                }

bluetoothStateChangeHandler() 负责更新状态，并发送状态变化的广播。

3.2.1.3 Callback Invoke Example

回调方法执行的源码如下
packages/apps/Bluetooth/src/com/android/bluetooth/btservice/AdapterService.java

    void updateAdapterState(int prevState, int newState) {
......
        if (mCallbacks != null) {
            int n = mCallbacks.beginBroadcast();
            for (int i = 0; i < n; i++) {
                try {
                    mCallbacks.getBroadcastItem(i).onBluetoothStateChange(prevState, newState);
                } catch (RemoteException e) {
......
                }
            }
            mCallbacks.finishBroadcast();
        }

frameworks/base/core/java/android/os/RemoteCallbackList.java

public class RemoteCallbackList {

    public int beginBroadcast() {
        synchronized (mCallbacks) {         
            final int N = mBroadcastCount = mCallbacks.size();
            if (N <= 0) {
                return 0;
            }
            Object[] active = mActiveBroadcast;
            if (active == null || active.length < N) {
                mActiveBroadcast = active = new Object[N];
            }
            for (int i=0; i

3.2.2 sendBluetoothServiceUpCallback

frameworks/base/services/core/java/com/android/server/BluetoothManagerService.java

    private final RemoteCallbackList mCallbacks = 
            new RemoteCallbackList();;

    private void sendBluetoothServiceUpCallback() {
        synchronized (mCallbacks) {
            try {
                int n = mCallbacks.beginBroadcast();
                for (int i = 0; i < n; i++) {
                    try {
                        mCallbacks.getBroadcastItem(i).onBluetoothServiceUp(mBluetooth);
                    } catch (RemoteException e) {
                        Slog.e(TAG, "Unable to call onBluetoothServiceUp() on callback #" + i, e);
                    }
                }
            } finally {
                mCallbacks.finishBroadcast();
            }
        }
    }

BluetoothManagerService 回调应用层注册的回调对象的方法 onBluetoothServiceUp()，将蓝牙进程入口的代理对象发送到该应用。

frameworks/base/core/java/android/bluetooth/BluetoothDevice.java

public final class BluetoothDevice implements Parcelable {

    static IBluetoothManagerCallback sStateChangeCallback = new IBluetoothManagerCallback.Stub() {

        public void onBluetoothServiceUp(IBluetooth bluetoothService)
                throws RemoteException {
            synchronized (BluetoothDevice.class) {
                if (sService == null) {
                    sService = bluetoothService;
                }
            }
        }
        ......
    }
}

3.2.3 Bluetooth Process enable

蓝牙进程继续执行 enable 操作的内容较多，链接如下。
Bluetooth initialization - enable in Bluetooth process