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      1 /*
      2  * Copyright (C) 2013 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 android.util;
     18 
     19 import android.os.SystemClock;
     20 
     21 import java.util.concurrent.TimeoutException;
     22 
     23 /**
     24  * This is a helper class for making an async one way call and
     25  * its async one way response response in a sync fashion within
     26  * a timeout. The key idea is to call the remote method with a
     27  * sequence number and a callback and then starting to wait for
     28  * the response. The remote method calls back with the result and
     29  * the sequence number. If the response comes within the timeout
     30  * and its sequence number is the one sent in the method invocation,
     31  * then the call succeeded. If the response does not come within
     32  * the timeout then the call failed. Older result received when
     33  * waiting for the result are ignored.
     34  * <p>
     35  * Typical usage is:
     36  * </p>
     37  * <p><pre><code>
     38  * public class MyMethodCaller extends TimeoutRemoteCallHelper<Object> {
     39  *     // The one way remote method to call.
     40  *     private final IRemoteInterface mTarget;
     41  *
     42  *     // One way callback invoked when the remote method is done.
     43  *     private final IRemoteCallback mCallback = new IRemoteCallback.Stub() {
     44  *         public void onCompleted(Object result, int sequence) {
     45  *             onRemoteMethodResult(result, sequence);
     46  *         }
     47  *     };
     48  *
     49  *     public MyMethodCaller(IRemoteInterface target) {
     50  *         mTarget = target;
     51  *     }
     52  *
     53  *     public Object onCallMyMethod(Object arg) throws RemoteException {
     54  *         final int sequence = onBeforeRemoteCall();
     55  *         mTarget.myMethod(arg, sequence);
     56  *         return getResultTimed(sequence);
     57  *     }
     58  * }
     59  * </code></pre></p>
     60  *
     61  * @param <T> The type of the expected result.
     62  *
     63  * @hide
     64  */
     65 public abstract class TimedRemoteCaller<T> {
     66 
     67     public static final long DEFAULT_CALL_TIMEOUT_MILLIS = 5000;
     68 
     69     private static final int UNDEFINED_SEQUENCE = -1;
     70 
     71     private final Object mLock = new Object();
     72 
     73     private final long mCallTimeoutMillis;
     74 
     75     private int mSequenceCounter;
     76 
     77     private int mReceivedSequence = UNDEFINED_SEQUENCE;
     78 
     79     private int mAwaitedSequence = UNDEFINED_SEQUENCE;
     80 
     81     private T mResult;
     82 
     83     public TimedRemoteCaller(long callTimeoutMillis) {
     84         mCallTimeoutMillis = callTimeoutMillis;
     85     }
     86 
     87     public final int onBeforeRemoteCall() {
     88         synchronized (mLock) {
     89             mAwaitedSequence = mSequenceCounter++;
     90             return mAwaitedSequence;
     91         }
     92     }
     93 
     94     public final T getResultTimed(int sequence) throws TimeoutException {
     95         synchronized (mLock) {
     96             final boolean success = waitForResultTimedLocked(sequence);
     97             if (!success) {
     98                 throw new TimeoutException("No reponse for sequence: " + sequence);
     99             }
    100             T result = mResult;
    101             mResult = null;
    102             return result;
    103         }
    104     }
    105 
    106     public final void onRemoteMethodResult(T result, int sequence) {
    107         synchronized (mLock) {
    108             if (sequence == mAwaitedSequence) {
    109                 mReceivedSequence = sequence;
    110                 mResult = result;
    111                 mLock.notifyAll();
    112             }
    113         }
    114     }
    115 
    116     private boolean waitForResultTimedLocked(int sequence) {
    117         final long startMillis = SystemClock.uptimeMillis();
    118         while (true) {
    119             try {
    120                 if (mReceivedSequence == sequence) {
    121                     return true;
    122                 }
    123                 final long elapsedMillis = SystemClock.uptimeMillis() - startMillis;
    124                 final long waitMillis = mCallTimeoutMillis - elapsedMillis;
    125                 if (waitMillis <= 0) {
    126                     return false;
    127                 }
    128                 mLock.wait(waitMillis);
    129             } catch (InterruptedException ie) {
    130                 /* ignore */
    131             }
    132         }
    133     }
    134 }
    135