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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License
     15  */
     16 
     17 package com.android.server.location;
     18 
     19 import com.android.internal.util.Preconditions;
     20 
     21 import android.annotation.NonNull;
     22 import android.os.IBinder;
     23 import android.os.IInterface;
     24 import android.os.RemoteException;
     25 import android.util.Log;
     26 
     27 import java.util.ArrayList;
     28 import java.util.Collection;
     29 import java.util.HashMap;
     30 
     31 /**
     32  * A helper class, that handles operations in remote listeners, and tracks for remote process death.
     33  */
     34 abstract class RemoteListenerHelper<TListener extends IInterface> {
     35     private final String mTag;
     36     private final HashMap<IBinder, LinkedListener> mListenerMap =
     37             new HashMap<IBinder, LinkedListener>();
     38 
     39     protected RemoteListenerHelper(String name) {
     40         Preconditions.checkNotNull(name);
     41         mTag = name;
     42     }
     43 
     44     public boolean addListener(@NonNull TListener listener) {
     45         Preconditions.checkNotNull(listener, "Attempted to register a 'null' listener.");
     46         if (!isSupported()) {
     47             Log.e(mTag, "Refused to add listener, the feature is not supported.");
     48             return false;
     49         }
     50 
     51         IBinder binder = listener.asBinder();
     52         LinkedListener deathListener = new LinkedListener(listener);
     53         synchronized (mListenerMap) {
     54             if (mListenerMap.containsKey(binder)) {
     55                 // listener already added
     56                 return true;
     57             }
     58 
     59             try {
     60                 binder.linkToDeath(deathListener, 0 /* flags */);
     61             } catch (RemoteException e) {
     62                 // if the remote process registering the listener is already death, just swallow the
     63                 // exception and continue
     64                 Log.e(mTag, "Remote listener already died.", e);
     65                 return false;
     66             }
     67 
     68             mListenerMap.put(binder, deathListener);
     69             if (mListenerMap.size() == 1) {
     70                 if (!registerWithService()) {
     71                     Log.e(mTag, "RegisterWithService failed, listener will be removed.");
     72                     removeListener(listener);
     73                     return false;
     74                 }
     75             }
     76         }
     77 
     78         return true;
     79     }
     80 
     81     public boolean removeListener(@NonNull TListener listener) {
     82         Preconditions.checkNotNull(listener, "Attempted to remove a 'null' listener.");
     83         if (!isSupported()) {
     84             Log.e(mTag, "Refused to remove listener, the feature is not supported.");
     85             return false;
     86         }
     87 
     88         IBinder binder = listener.asBinder();
     89         LinkedListener linkedListener;
     90         synchronized (mListenerMap) {
     91             linkedListener = mListenerMap.remove(binder);
     92             if (mListenerMap.isEmpty() && linkedListener != null) {
     93                 unregisterFromService();
     94             }
     95         }
     96 
     97         if (linkedListener != null) {
     98             binder.unlinkToDeath(linkedListener, 0 /* flags */);
     99         }
    100         return true;
    101     }
    102 
    103     protected abstract boolean isSupported();
    104     protected abstract boolean registerWithService();
    105     protected abstract void unregisterFromService();
    106 
    107     protected interface ListenerOperation<TListener extends IInterface> {
    108         void execute(TListener listener) throws RemoteException;
    109     }
    110 
    111     protected void foreach(ListenerOperation operation) {
    112         Collection<LinkedListener> linkedListeners;
    113         synchronized (mListenerMap) {
    114             Collection<LinkedListener> values = mListenerMap.values();
    115             linkedListeners = new ArrayList<LinkedListener>(values);
    116         }
    117 
    118         for (LinkedListener linkedListener : linkedListeners) {
    119             TListener listener = linkedListener.getUnderlyingListener();
    120             try {
    121                 operation.execute(listener);
    122             } catch (RemoteException e) {
    123                 Log.e(mTag, "Error in monitored listener.", e);
    124                 removeListener(listener);
    125             }
    126         }
    127     }
    128 
    129     private class LinkedListener implements IBinder.DeathRecipient {
    130         private final TListener mListener;
    131 
    132         public LinkedListener(@NonNull TListener listener) {
    133             mListener = listener;
    134         }
    135 
    136         @NonNull
    137         public TListener getUnderlyingListener() {
    138             return mListener;
    139         }
    140 
    141         @Override
    142         public void binderDied() {
    143             Log.d(mTag, "Remote Listener died: " + mListener);
    144             removeListener(mListener);
    145         }
    146     }
    147 }
    148