sdk/sources/android-25/android/util/TimedRemoteCaller.java

   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 }