1 /*
2 * Copyright (C) 2009 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15 package com.google.common.util.concurrent;
16
17 import static com.google.common.util.concurrent.Internal.toNanosSaturated;
18
19 import com.google.common.annotations.GwtIncompatible;
20 import com.google.errorprone.annotations.CanIgnoreReturnValue;
21 import com.google.errorprone.annotations.DoNotMock;
22 import java.time.Duration;
23 import java.util.concurrent.Executor;
24 import java.util.concurrent.TimeUnit;
25 import java.util.concurrent.TimeoutException;
26
27 /**
28 * An object with an operational state, plus asynchronous {@link #startAsync()} and {@link
29 * #stopAsync()} lifecycle methods to transition between states. Example services include
30 * webservers, RPC servers and timers.
31 *
32 * <p>The normal lifecycle of a service is:
33 *
34 * <ul>
35 * <li>{@linkplain State#NEW NEW} ->
36 * <li>{@linkplain State#STARTING STARTING} ->
37 * <li>{@linkplain State#RUNNING RUNNING} ->
38 * <li>{@linkplain State#STOPPING STOPPING} ->
39 * <li>{@linkplain State#TERMINATED TERMINATED}
40 * </ul>
41 *
42 * <p>There are deviations from this if there are failures or if {@link Service#stopAsync} is called
43 * before the {@link Service} reaches the {@linkplain State#RUNNING RUNNING} state. The set of legal
44 * transitions form a <a href="http://en.wikipedia.org/wiki/Directed_acyclic_graph">DAG</a>,
45 * therefore every method of the listener will be called at most once. N.B. The {@link State#FAILED}
46 * and {@link State#TERMINATED} states are terminal states, once a service enters either of these
47 * states it cannot ever leave them.
48 *
49 * <p>Implementors of this interface are strongly encouraged to extend one of the abstract classes
50 * in this package which implement this interface and make the threading and state management
51 * easier.
52 *
53 * @author Jesse Wilson
54 * @author Luke Sandberg
55 * @since 9.0 (in 1.0 as {@code com.google.common.base.Service})
56 */
57 @DoNotMock("Create an AbstractIdleService")
58 @GwtIncompatible
59 @ElementTypesAreNonnullByDefault
60 public interface Service {
61 /**
62 * If the service state is {@link State#NEW}, this initiates service startup and returns
63 * immediately. A stopped service may not be restarted.
64 *
65 * @return this
66 * @throws IllegalStateException if the service is not {@link State#NEW}
67 * @since 15.0
68 */
69 @CanIgnoreReturnValue
70 Service startAsync();
71
72 /** Returns {@code true} if this service is {@linkplain State#RUNNING running}. */
73 boolean isRunning();
74
75 /** Returns the lifecycle state of the service. */
76 State state();
77
78 /**
79 * If the service is {@linkplain State#STARTING starting} or {@linkplain State#RUNNING running},
80 * this initiates service shutdown and returns immediately. If the service is {@linkplain
81 * State#NEW new}, it is {@linkplain State#TERMINATED terminated} without having been started nor
82 * stopped. If the service has already been stopped, this method returns immediately without
83 * taking action.
84 *
85 * @return this
86 * @since 15.0
87 */
88 @CanIgnoreReturnValue
89 Service stopAsync();
90
91 /**
92 * Waits for the {@link Service} to reach the {@linkplain State#RUNNING running state}.
93 *
94 * @throws IllegalStateException if the service reaches a state from which it is not possible to
95 * enter the {@link State#RUNNING} state. e.g. if the {@code state} is {@code
96 * State#TERMINATED} when this method is called then this will throw an IllegalStateException.
97 * @since 15.0
98 */
99 void awaitRunning();
100
101 /**
102 * Waits for the {@link Service} to reach the {@linkplain State#RUNNING running state} for no more
103 * than the given time.
104 *
105 * @param timeout the maximum time to wait
106 * @throws TimeoutException if the service has not reached the given state within the deadline
107 * @throws IllegalStateException if the service reaches a state from which it is not possible to
108 * enter the {@link State#RUNNING RUNNING} state. e.g. if the {@code state} is {@code
109 * State#TERMINATED} when this method is called then this will throw an IllegalStateException.
110 * @since 28.0
111 */
112 default void awaitRunning(Duration timeout) throws TimeoutException {
113 awaitRunning(toNanosSaturated(timeout), TimeUnit.NANOSECONDS);
114 }
115
116 /**
117 * Waits for the {@link Service} to reach the {@linkplain State#RUNNING running state} for no more
118 * than the given time.
119 *
120 * @param timeout the maximum time to wait
121 * @param unit the time unit of the timeout argument
122 * @throws TimeoutException if the service has not reached the given state within the deadline
123 * @throws IllegalStateException if the service reaches a state from which it is not possible to
124 * enter the {@link State#RUNNING RUNNING} state. e.g. if the {@code state} is {@code
125 * State#TERMINATED} when this method is called then this will throw an IllegalStateException.
126 * @since 15.0
127 */
128 @SuppressWarnings("GoodTime") // should accept a java.time.Duration
129 void awaitRunning(long timeout, TimeUnit unit) throws TimeoutException;
130
131 /**
132 * Waits for the {@link Service} to reach the {@linkplain State#TERMINATED terminated state}.
133 *
134 * @throws IllegalStateException if the service {@linkplain State#FAILED fails}.
135 * @since 15.0
136 */
137 void awaitTerminated();
138
139 /**
140 * Waits for the {@link Service} to reach a terminal state (either {@link Service.State#TERMINATED
141 * terminated} or {@link Service.State#FAILED failed}) for no more than the given time.
142 *
143 * @param timeout the maximum time to wait
144 * @throws TimeoutException if the service has not reached the given state within the deadline
145 * @throws IllegalStateException if the service {@linkplain State#FAILED fails}.
146 * @since 28.0
147 */
148 default void awaitTerminated(Duration timeout) throws TimeoutException {
149 awaitTerminated(toNanosSaturated(timeout), TimeUnit.NANOSECONDS);
150 }
151
152 /**
153 * Waits for the {@link Service} to reach a terminal state (either {@link Service.State#TERMINATED
154 * terminated} or {@link Service.State#FAILED failed}) for no more than the given time.
155 *
156 * @param timeout the maximum time to wait
157 * @param unit the time unit of the timeout argument
158 * @throws TimeoutException if the service has not reached the given state within the deadline
159 * @throws IllegalStateException if the service {@linkplain State#FAILED fails}.
160 * @since 15.0
161 */
162 @SuppressWarnings("GoodTime") // should accept a java.time.Duration
163 void awaitTerminated(long timeout, TimeUnit unit) throws TimeoutException;
164
165 /**
166 * Returns the {@link Throwable} that caused this service to fail.
167 *
168 * @throws IllegalStateException if this service's state isn't {@linkplain State#FAILED FAILED}.
169 * @since 14.0
170 */
171 Throwable failureCause();
172
173 /**
174 * Registers a {@link Listener} to be {@linkplain Executor#execute executed} on the given
175 * executor. The listener will have the corresponding transition method called whenever the
176 * service changes state. The listener will not have previous state changes replayed, so it is
177 * suggested that listeners are added before the service starts.
178 *
179 * <p>{@code addListener} guarantees execution ordering across calls to a given listener but not
180 * across calls to multiple listeners. Specifically, a given listener will have its callbacks
181 * invoked in the same order as the underlying service enters those states. Additionally, at most
182 * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks
183 * may execute concurrently, and listeners may execute in an order different from the one in which
184 * they were registered.
185 *
186 * <p>RuntimeExceptions thrown by a listener will be caught and logged. Any exception thrown
187 * during {@code Executor.execute} (e.g., a {@code RejectedExecutionException}) will be caught and
188 * logged.
189 *
190 * @param listener the listener to run when the service changes state is complete
191 * @param executor the executor in which the listeners callback methods will be run. For fast,
192 * lightweight listeners that would be safe to execute in any thread, consider {@link
193 * MoreExecutors#directExecutor}.
194 * @since 13.0
195 */
196 void addListener(Listener listener, Executor executor);
197
198 /**
199 * The lifecycle states of a service.
200 *
201 * <p>The ordering of the {@link State} enum is defined such that if there is a state transition
202 * from {@code A -> B} then {@code A.compareTo(B) < 0}. N.B. The converse is not true, i.e. if
203 * {@code A.compareTo(B) < 0} then there is <b>not</b> guaranteed to be a valid state transition
204 * {@code A -> B}.
205 *
206 * @since 9.0 (in 1.0 as {@code com.google.common.base.Service.State})
207 */
208 enum State {
209 /** A service in this state is inactive. It does minimal work and consumes minimal resources. */
210 NEW,
211
212 /** A service in this state is transitioning to {@link #RUNNING}. */
213 STARTING,
214
215 /** A service in this state is operational. */
216 RUNNING,
217
218 /** A service in this state is transitioning to {@link #TERMINATED}. */
219 STOPPING,
220
221 /**
222 * A service in this state has completed execution normally. It does minimal work and consumes
223 * minimal resources.
224 */
225 TERMINATED,
226
227 /**
228 * A service in this state has encountered a problem and may not be operational. It cannot be
229 * started nor stopped.
230 */
231 FAILED,
232 }
233
234 /**
235 * A listener for the various state changes that a {@link Service} goes through in its lifecycle.
236 *
237 * <p>All methods are no-ops by default, implementors should override the ones they care about.
238 *
239 * @author Luke Sandberg
240 * @since 15.0 (present as an interface in 13.0)
241 */
242 abstract class Listener {
243 /**
244 * Called when the service transitions from {@linkplain State#NEW NEW} to {@linkplain
245 * State#STARTING STARTING}. This occurs when {@link Service#startAsync} is called the first
246 * time.
247 */
248 public void starting() {}
249
250 /**
251 * Called when the service transitions from {@linkplain State#STARTING STARTING} to {@linkplain
252 * State#RUNNING RUNNING}. This occurs when a service has successfully started.
253 */
254 public void running() {}
255
256 /**
257 * Called when the service transitions to the {@linkplain State#STOPPING STOPPING} state. The
258 * only valid values for {@code from} are {@linkplain State#STARTING STARTING} or {@linkplain
259 * State#RUNNING RUNNING}. This occurs when {@link Service#stopAsync} is called.
260 *
261 * @param from The previous state that is being transitioned from.
262 */
263 public void stopping(State from) {}
264
265 /**
266 * Called when the service transitions to the {@linkplain State#TERMINATED TERMINATED} state.
267 * The {@linkplain State#TERMINATED TERMINATED} state is a terminal state in the transition
268 * diagram. Therefore, if this method is called, no other methods will be called on the {@link
269 * Listener}.
270 *
271 * @param from The previous state that is being transitioned from. Failure can occur in any
272 * state with the exception of {@linkplain State#FAILED FAILED} and {@linkplain
273 * State#TERMINATED TERMINATED}.
274 */
275 public void terminated(State from) {}
276
277 /**
278 * Called when the service transitions to the {@linkplain State#FAILED FAILED} state. The
279 * {@linkplain State#FAILED FAILED} state is a terminal state in the transition diagram.
280 * Therefore, if this method is called, no other methods will be called on the {@link Listener}.
281 *
282 * @param from The previous state that is being transitioned from. Failure can occur in any
283 * state with the exception of {@linkplain State#NEW NEW} or {@linkplain State#TERMINATED
284 * TERMINATED}.
285 * @param failure The exception that caused the failure.
286 */
287 public void failed(State from, Throwable failure) {}
288 }
289 }