IPC進程間通信的使用(六)—Binder連接池

之前幾篇文章分別寫了幾種不同的IPC方式，不同的方式有不同的特點和使用場景。
在進程間通信是，AIDL是首選。很多時候開發過程中不僅僅至於要一個ADIL接口，當接口過多的時候需要創建多個Service，這樣就比較不方便而且佔用系統資源。所以又出現了Binder連接池。這裏簡單記錄一下使用方法。
工作機制是：每個業務模塊創建自己的AIDL接口，並實現此接口，這時候不同業務模塊之間是不能有耦合的，所以實現細節都要單獨開來，然後向服務端提供自己的唯一標識和其對於的Binder對象。對於服務端來說，只需要一個Service即可，服務端提供一個queryBinder接口，這個接口能夠根據業務模塊的特徵來返回相應的Binder對象給它們，不同的業務模塊拿到所需的Binder對象後就可以進行遠程方法調用了。由此可見，Binder連接池的主要作用就是將每個業務模塊的Binder請求統一轉發的遠程Service中去執行，從而避免了重複創建的過程。

個人理解：Binder連接池就是一箇中轉站，通過Binder連接池來實現AIDL接口和Service的交互。

舉個例子：
創建兩個ADIL接口：分佈是ISecurityCenter.aild, ICompute.aidl

// ISecurityCenter.aidl
package com.kevin.testaidl;

// Declare any non-default types here with import statements

interface ISecurityCenter {
String encrypt(String content);
String decrypt(String password);

}
————————————————————————————————
// ICompute.aidl
package com.kevin.testaidl;

// Declare any non-default types here with import statements

interface ICompute {
  int add(int a,int b);
}

分佈爲上面兩個接口創建實現類：

/**
 * Created by Kevin on 2019/4/11<br/>
 * Blog:https://blog.csdn.net/student9128<br/>
 * Describe:<br/>
 */
public class SecurityCenterImpl extends ISecurityCenter.Stub {
    private static final char SECRET_CODE = '^';

    @Override
    public String encrypt(String content) throws RemoteException {
        char[] chars = content.toCharArray();
        for (int i = 0; i < chars.length; i++) {
            chars[i] ^= SECRET_CODE;
        }
        return new String(chars);
    }

    @Override
    public String decrypt(String password) throws RemoteException {
        return encrypt(password);
    }
}


—————————————————————
/**
 * Created by Kevin on 2019/4/11<br/>
 * Blog:https://blog.csdn.net/student9128<br/>
 * Describe:<br/>
 */
public class ComputeImpl extends ICompute.Stub {
    @Override
    public int add(int a, int b) throws RemoteException {
        return a+b;
    }
}

再創建一個IBinderPool.aidl

// IBinderPool.aidl
package com.kevin.testaidl;

// Declare any non-default types here with import statements

interface IBinderPool {
/**
 * @param binderCode,the unique token of specific Binder<br/>
 * @return specific Binder who's token is binderCode.
 */
IBinder queryBinder(int binderCode);
}

創建一個BinderPool類：
該類中實現了一個單例方法，保證BinderPool初始化一次，初始中進行了connectBinderPoolService對Binder池進行綁定。同時內部創建了一個靜態內部類BinderPoolImpl類實現了queryBinde接口，該方法中主要通過binderConder獲取相關的AIDL接口實現類，如代碼所示。

/**
 * Created by Kevin on 2019/4/11<br/>
 * Blog:https://blog.csdn.net/student9128<br/>
 * Describe:<br/>
 */
public class BinderPool {
    private static final String TAG = "BinderPool";
    public static final int BINDER_NONE = -1;
    public static final int BINDER_COMPUTE = 0;
    public static final int BINDER_SECURITY_CENTER = 1;
    private Context mContext;
    private IBinderPool mBinderPool;
    private static volatile BinderPool sInstance;
    private CountDownLatch mConnectBinderPoolCountDownLatch;

    private BinderPool(Context context) {
        mContext = context.getApplicationContext();
        connectBinderPoolService();
    }

    public static BinderPool getInstance(Context context) {
        if (sInstance == null) {
            synchronized (BinderPool.class) {
                sInstance = new BinderPool(context);
            }
        }
        return sInstance;
    }

    /**
     * 綁定Binder池服務
     */
    private synchronized void connectBinderPoolService() {
        mConnectBinderPoolCountDownLatch = new CountDownLatch(1);
        Intent service = new Intent(mContext, BinderPoolService.class);
        mContext.bindService(service, mBinderPoolConnection, Context.BIND_AUTO_CREATE);
        try {
            mConnectBinderPoolCountDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }

    /**
     * 根據binderCode來查詢Binder
     * @param binderCode
     * @return Binder
     */
    public IBinder queryBinder(int binderCode) {
        if (mBinderPool != null) {
            try {
                return mBinderPool.queryBinder(binderCode);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }else {
            //爲null
        }
        return null;
    }

    private ServiceConnection mBinderPoolConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {

            mBinderPool = IBinderPool.Stub.asInterface(service);
            try {
                mBinderPool.asBinder().linkToDeath(mBinderPoolDeathRecipient, 0);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
            mConnectBinderPoolCountDownLatch.countDown();
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
        }
    };
    /**
     * Binder意外死亡，重新連接服務
     */
    private IBinder.DeathRecipient mBinderPoolDeathRecipient = new IBinder.DeathRecipient() {
        @Override
        public void binderDied() {
            mBinderPool.asBinder().unlinkToDeath(mBinderPoolDeathRecipient, 0);
            mBinderPool = null;
            connectBinderPoolService();//重新連接服務
        }
    };

    public static class BinderPoolImpl extends IBinderPool.Stub {
        public BinderPoolImpl() {
            super();
        }

        @Override
        public IBinder queryBinder(int binderCode) throws RemoteException {
            switch (binderCode) {
                case BINDER_NONE:
                    return null;
                case BINDER_COMPUTE:
                    return new ComputeImpl();
                case BINDER_SECURITY_CENTER:
                    return new SecurityCenterImpl();
                default:
                    return null;
            }
        }
    }

}

服務端：
Service會根據queryBinder在onBind中返回相對應的相關的IBinder對象

public class BinderPoolService extends Service {
    private static final String TAG = "BinderPoolService";
    private Binder mBinderPool = new BinderPool.BinderPoolImpl();

    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Override
    public IBinder onBind(Intent intent) {
        return mBinderPool;
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }
}

客戶端：
通過 BinderPool binderPool = BinderPool.getInstance(this);來連接服務，綁定Binder連接池。
通過 binderCode來獲取相關的Binder，去調用相對於的服務，如下代碼所示

/**
 * Created by Kevin on 2019/4/11<br/>
 * Blog:https://blog.csdn.net/student9128<br/>
 * Describe:<br/>
 */
public class BinderPoolActivity extends AppCompatActivity {
    private final String TAG = getClass().getSimpleName();
    private ISecurityCenter mSecurityCenter;
    private ICompute mCompute;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = findViewById(R.id.btn);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Thread() {
                    @Override
                    public void run() {
                        super.run();
                        doWork();
                    }
                }.start();
            }
        });
    }

    private void doWork() {
        BinderPool binderPool = BinderPool.getInstance(this);
        IBinder securityBinder = binderPool.queryBinder(BinderPool.BINDER_SECURITY_CENTER);//注意此處，不同的binderCode
        mSecurityCenter = SecurityCenterImpl.asInterface(securityBinder);
        try {
            String encryptStr = mSecurityCenter.encrypt("Hello Android");
            Log.d(TAG, "encryptStr=" + encryptStr);
            String decryptStr = mSecurityCenter.decrypt(encryptStr);
            Log.d(TAG, "decryptStr=" + decryptStr);
        } catch (RemoteException e) {
            e.printStackTrace();
        }
        Log.d(TAG, "execute compute method");
        IBinder computeBinder = binderPool.queryBinder(BinderPool.BINDER_COMPUTE);//注意此處，不同的binderCode
        mCompute = ComputeImpl.asInterface(computeBinder);
        try {
            int addResult = mCompute.add(2, 3);
            Log.d(TAG, "2+3=" + addResult);
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }
}

Binder連接池的實現中，通過CountDownLatch將binderService這一異步操作轉換成了同步操作，這就意味着可能是耗時的，所以調用的過程中開了一個線程

注：本文章知識點來自學習《Android開發藝術探索》一書