java/src/main/com/google/appengine/tools/development/TimedFuture.java

   1 // Copyright 2011 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.tools.development;
   4
   5 import java.util.concurrent.ExecutionException;
   6 import java.util.concurrent.TimeoutException;
   7 import java.util.concurrent.TimeUnit;
   8 import java.util.concurrent.Future;
   9
  10 /**
  11  * {@code TimedFuture} is a {@link Future} that will not return
  12  * successfully after the specified amount of time has elapsed.
  13  *
  14  * <p>All methods call through to the underlying future.  However, if
  15  * the specified time elapses (either before or while in one of the
  16  * {@code get} methods), an ExecutionException will be thrown that
  17  * wraps the exception returned by {@link #createDeadlineException()}.
  18  * No attempt is made to automatically cancel the underlying Future in
  19  * this case.
  20  *
  21  */
  22 public abstract class TimedFuture<T> implements Future<T> {
  23   private final Future<T> future;
  24   private final Clock clock;
  25   private final long deadlineTime;
  26
  27   public TimedFuture(Future<T> future, long deadlineMillis) {
  28     this(future, deadlineMillis, Clock.DEFAULT);
  29   }
  30
  31   public TimedFuture(Future<T> future, long deadlineMillis, Clock clock) {
  32     this.future = future;
  33     this.deadlineTime = clock.getCurrentTime() + deadlineMillis;
  34     this.clock = clock;
  35   }
  36
  37   @Override
  38   public T get() throws InterruptedException, ExecutionException {
  39     long millisRemaining = getMillisRemaining();
  40     try {
  41       return future.get(millisRemaining, TimeUnit.MILLISECONDS);
  42     } catch (TimeoutException ex) {
  43       throw new ExecutionException(createDeadlineException());
  44     }
  45   }
  46
  47   @Override
  48   public T get(long value, TimeUnit units)
  49       throws InterruptedException, ExecutionException, TimeoutException {
  50     long millisRequested = units.toMillis(value);
  51     long millisRemaining = getMillisRemaining();
  52     if (millisRequested < millisRemaining) {
  53       return future.get(millisRequested, TimeUnit.MILLISECONDS);
  54     }
  55     try {
  56       return future.get(millisRemaining, TimeUnit.MILLISECONDS);
  57     } catch (TimeoutException ex) {
  58       throw new ExecutionException(createDeadlineException());
  59     }
  60   }
  61
  62   protected abstract RuntimeException createDeadlineException();
  63
  64   private long getMillisRemaining() {
  65     return Math.max(0, deadlineTime - clock.getCurrentTime());
  66   }
  67
  68   @Override
  69   public boolean isCancelled() {
  70     return future.isCancelled();
  71   }
  72
  73   @Override
  74   public boolean isDone() {
  75     return future.isDone() || getMillisRemaining() == 0;
  76   }
  77
  78   @Override
  79   public boolean cancel(boolean force) {
  80     return future.cancel(force);
  81   }
  82 }