1 /*
2 * Copyright (C) 2012 The Guava Authors
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.google.common.util.concurrent.testing;
18
19 import com.google.common.annotations.Beta;
20 import com.google.common.annotations.GwtIncompatible;
21 import com.google.common.collect.ImmutableList;
22 import com.google.common.primitives.Longs;
23 import com.google.common.util.concurrent.AbstractFuture;
24 import com.google.common.util.concurrent.AbstractListeningExecutorService;
25 import com.google.common.util.concurrent.ListenableScheduledFuture;
26 import com.google.common.util.concurrent.ListeningScheduledExecutorService;
27 import com.google.common.util.concurrent.MoreExecutors;
28 import java.util.List;
29 import java.util.concurrent.Callable;
30 import java.util.concurrent.Delayed;
31 import java.util.concurrent.ScheduledFuture;
32 import java.util.concurrent.TimeUnit;
33
34 /**
35 * Factory methods for {@link ExecutorService} for testing.
36 *
37 * @author Chris Nokleberg
38 * @since 14.0
39 */
40 @Beta
41 @GwtIncompatible
42 public final class TestingExecutors {
43 private TestingExecutors() {}
44
45 /**
46 * Returns a {@link ScheduledExecutorService} that never executes anything.
47 *
48 * <p>The {@code shutdownNow} method of the returned executor always returns an empty list despite
49 * the fact that everything is still technically awaiting execution. The {@code getDelay} method
50 * of any {@link ScheduledFuture} returned by the executor will always return the max long value
51 * instead of the time until the user-specified delay.
52 */
53 public static ListeningScheduledExecutorService noOpScheduledExecutor() {
54 return new NoOpScheduledExecutorService();
55 }
56
57 /**
58 * Creates a scheduled executor service that runs each task in the thread that invokes {@code
59 * execute/submit/schedule}, as in {@link CallerRunsPolicy}. This applies both to individually
60 * submitted tasks and to collections of tasks submitted via {@code invokeAll}, {@code invokeAny},
61 * {@code schedule}, {@code scheduleAtFixedRate}, and {@code scheduleWithFixedDelay}. In the case
62 * of tasks submitted by {@code invokeAll} or {@code invokeAny}, tasks will run serially on the
63 * calling thread. Tasks are run to completion before a {@code Future} is returned to the caller
64 * (unless the executor has been shutdown).
65 *
66 * <p>The returned executor is backed by the executor returned by {@link
67 * MoreExecutors#newDirectExecutorService} and subject to the same constraints.
68 *
69 * <p>Although all tasks are immediately executed in the thread that submitted the task, this
70 * {@code ExecutorService} imposes a small locking overhead on each task submission in order to
71 * implement shutdown and termination behavior.
72 *
73 * <p>Because of the nature of single-thread execution, the methods {@code scheduleAtFixedRate}
74 * and {@code scheduleWithFixedDelay} are not supported by this class and will throw an
75 * UnsupportedOperationException.
76 *
77 * <p>The implementation deviates from the {@code ExecutorService} specification with regards to
78 * the {@code shutdownNow} method. First, "best-effort" with regards to canceling running tasks is
79 * implemented as "no-effort". No interrupts or other attempts are made to stop threads executing
80 * tasks. Second, the returned list will always be empty, as any submitted task is considered to
81 * have started execution. This applies also to tasks given to {@code invokeAll} or {@code
82 * invokeAny} which are pending serial execution, even the subset of the tasks that have not yet
83 * started execution. It is unclear from the {@code ExecutorService} specification if these should
84 * be included, and it's much easier to implement the interpretation that they not be. Finally, a
85 * call to {@code shutdown} or {@code shutdownNow} may result in concurrent calls to {@code
86 * invokeAll/invokeAny} throwing RejectedExecutionException, although a subset of the tasks may
87 * already have been executed.
88 *
89 * @since 15.0
90 */
91 public static SameThreadScheduledExecutorService sameThreadScheduledExecutor() {
92 return new SameThreadScheduledExecutorService();
93 }
94
95 private static final class NoOpScheduledExecutorService extends AbstractListeningExecutorService
96 implements ListeningScheduledExecutorService {
97
98 private volatile boolean shutdown;
99
100 @Override
101 public void shutdown() {
102 shutdown = true;
103 }
104
105 @Override
106 public List<Runnable> shutdownNow() {
107 shutdown();
108 return ImmutableList.of();
109 }
110
111 @Override
112 public boolean isShutdown() {
113 return shutdown;
114 }
115
116 @Override
117 public boolean isTerminated() {
118 return shutdown;
119 }
120
121 @Override
122 public boolean awaitTermination(long timeout, TimeUnit unit) {
123 return true;
124 }
125
126 @Override
127 public void execute(Runnable runnable) {}
128
129 @Override
130 public <V> ListenableScheduledFuture<V> schedule(
131 Callable<V> callable, long delay, TimeUnit unit) {
132 return NeverScheduledFuture.create();
133 }
134
135 @Override
136 public ListenableScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
137 return NeverScheduledFuture.create();
138 }
139
140 @Override
141 public ListenableScheduledFuture<?> scheduleAtFixedRate(
142 Runnable command, long initialDelay, long period, TimeUnit unit) {
143 return NeverScheduledFuture.create();
144 }
145
146 @Override
147 public ListenableScheduledFuture<?> scheduleWithFixedDelay(
148 Runnable command, long initialDelay, long delay, TimeUnit unit) {
149 return NeverScheduledFuture.create();
150 }
151
152 private static class NeverScheduledFuture<V> extends AbstractFuture<V>
153 implements ListenableScheduledFuture<V> {
154
155 static <V> NeverScheduledFuture<V> create() {
156 return new NeverScheduledFuture<V>();
157 }
158
159 @Override
160 public long getDelay(TimeUnit unit) {
161 return Long.MAX_VALUE;
162 }
163
164 @Override
165 public int compareTo(Delayed other) {
166 return Longs.compare(getDelay(TimeUnit.NANOSECONDS), other.getDelay(TimeUnit.NANOSECONDS));
167 }
168 }
169 }
170 }