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      1 /*
      2  * Copyright (C) 2017 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 package com.android.google.gce.gceservice;
     17 
     18 import android.util.Log;
     19 import java.util.ArrayList;
     20 import java.util.concurrent.CancellationException;
     21 import java.util.concurrent.ExecutionException;
     22 import java.util.concurrent.Future;
     23 import java.util.concurrent.TimeoutException;
     24 import java.util.concurrent.TimeUnit;
     25 
     26 public class GceFuture<T> implements Future<T> {
     27     private static final String LOG_TAG = "GceFuture";
     28     private boolean mDone = false;
     29     private Exception mException = null;
     30     private T mResult = null;
     31     private final String mName;
     32 
     33 
     34     public GceFuture(String name) {
     35         mName = name;
     36     }
     37 
     38 
     39     public String getName() {
     40         return mName;
     41     }
     42 
     43 
     44     public void set(T value) {
     45         synchronized(this) {
     46             if (mDone) {
     47                 Exception e = new Exception();
     48                 Log.e(LOG_TAG, mName + ": Multiple return values from a future object.", e);
     49                 return;
     50             }
     51 
     52             mResult = value;
     53             mDone = true;
     54             notifyAll();
     55         }
     56     }
     57 
     58 
     59     public void set(Exception e) {
     60         synchronized(this) {
     61             if (mDone) {
     62                 Log.w(LOG_TAG, mName + ": Discarding execution exception -- job done.", e);
     63                 return;
     64             }
     65 
     66             Log.w(LOG_TAG, mName + ": Could not complete job: " + e.getMessage(), e);
     67             mException = e;
     68             mDone = true;
     69             notifyAll();
     70         }
     71     }
     72 
     73 
     74     @Override
     75     public boolean cancel(boolean canInterrupt) {
     76         // We do not support interrupting jobs on purpose:
     77         // this offers us little benefit (stripping maybe a second or two), at the expense
     78         // of killing something that may cascade, like BroadcastReceiver.
     79         synchronized(this) {
     80             if (mDone) return false;
     81             set(new CancellationException("cancelled"));
     82         }
     83 
     84         return true;
     85     }
     86 
     87 
     88     @Override
     89     public boolean isCancelled() {
     90         synchronized(this) {
     91             return (mException != null) && (mException instanceof CancellationException);
     92         }
     93     }
     94 
     95 
     96     @Override
     97     public boolean isDone() {
     98         synchronized(this) {
     99             return mDone;
    100         }
    101     }
    102 
    103 
    104     @Override
    105     public T get() throws CancellationException, ExecutionException, InterruptedException {
    106         try {
    107             return get(-1, TimeUnit.SECONDS);
    108         } catch (TimeoutException e) {
    109             // This is a really interesting case to consider.
    110             // Fatal error to add to the drama.
    111             Log.wtf(LOG_TAG, mName + ": Unexpected condition: Infinite wait timed out.");
    112             return null;
    113         }
    114     }
    115 
    116 
    117     @Override
    118     public T get(long timeout, TimeUnit units)
    119     throws CancellationException, ExecutionException, InterruptedException, TimeoutException {
    120         waitDone(timeout, units);
    121 
    122         if (mException != null) {
    123             if (mException instanceof CancellationException)
    124                 throw (CancellationException)mException;
    125             throw new ExecutionException(mException);
    126         }
    127 
    128         return mResult;
    129     }
    130 
    131 
    132     /** Wait for final result.
    133      *
    134      * Result is considered available, when:
    135      * - provider returned value,
    136      * - this object was cancelled,
    137      * - provider threw an exception.
    138      */
    139     private void waitDone(long timeout, TimeUnit units)
    140             throws InterruptedException, TimeoutException {
    141         while (!mDone) {
    142             synchronized(this) {
    143                 if (timeout >= 0) {
    144                     this.wait(units.toMillis(timeout));
    145                     if (!mDone) throw new InterruptedException();
    146                 } else {
    147                     this.wait();
    148                 }
    149             }
    150         }
    151     }
    152 
    153 
    154     /** Convert list of GceFuture objects to string representation.
    155      */
    156     public static String toString(ArrayList<GceFuture<?>> futures) {
    157         StringBuilder b = new StringBuilder();
    158         for (GceFuture<?> dep : futures) {
    159             if (b.length() > 0) b.append(", ");
    160             b.append(dep.getName());
    161         }
    162 
    163         return b.toString();
    164     }
    165 }
    166