| /* |
| * Copyright (C) 2009 The Guava Authors |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.google.common.util.concurrent; |
| |
| import com.google.common.annotations.Beta; |
| |
| import java.util.concurrent.Executor; |
| import java.util.concurrent.TimeUnit; |
| import java.util.concurrent.TimeoutException; |
| |
| /** |
| * An object with an operational state, plus asynchronous {@link #startAsync()} and |
| * {@link #stopAsync()} lifecycle methods to transition between states. Example services include |
| * webservers, RPC servers and timers. |
| * |
| * <p>The normal lifecycle of a service is: |
| * <ul> |
| * <li>{@linkplain State#NEW NEW} -> |
| * <li>{@linkplain State#STARTING STARTING} -> |
| * <li>{@linkplain State#RUNNING RUNNING} -> |
| * <li>{@linkplain State#STOPPING STOPPING} -> |
| * <li>{@linkplain State#TERMINATED TERMINATED} |
| * </ul> |
| * |
| * <p>There are deviations from this if there are failures or if {@link Service#stopAsync} is called |
| * before the {@link Service} reaches the {@linkplain State#RUNNING RUNNING} state. The set of legal |
| * transitions form a <a href="http://en.wikipedia.org/wiki/Directed_acyclic_graph">DAG</a>, |
| * therefore every method of the listener will be called at most once. N.B. The {@link State#FAILED} |
| * and {@link State#TERMINATED} states are terminal states, once a service enters either of these |
| * states it cannot ever leave them. |
| * |
| * <p>Implementors of this interface are strongly encouraged to extend one of the abstract classes |
| * in this package which implement this interface and make the threading and state management |
| * easier. |
| * |
| * @author Jesse Wilson |
| * @author Luke Sandberg |
| * @since 9.0 (in 1.0 as {@code com.google.common.base.Service}) |
| */ |
| @Beta |
| public interface Service { |
| /** |
| * If the service state is {@link State#NEW}, this initiates service startup and returns |
| * immediately. A stopped service may not be restarted. |
| * |
| * @return this |
| * @throws IllegalStateException if the service is not {@link State#NEW} |
| * |
| * @since 15.0 |
| */ |
| Service startAsync(); |
| |
| /** |
| * Returns {@code true} if this service is {@linkplain State#RUNNING running}. |
| */ |
| boolean isRunning(); |
| |
| /** |
| * Returns the lifecycle state of the service. |
| */ |
| State state(); |
| |
| /** |
| * If the service is {@linkplain State#STARTING starting} or {@linkplain State#RUNNING running}, |
| * this initiates service shutdown and returns immediately. If the service is |
| * {@linkplain State#NEW new}, it is {@linkplain State#TERMINATED terminated} without having been |
| * started nor stopped. If the service has already been stopped, this method returns immediately |
| * without taking action. |
| * |
| * @return this |
| * @since 15.0 |
| */ |
| Service stopAsync(); |
| |
| /** |
| * Waits for the {@link Service} to reach the {@linkplain State#RUNNING running state}. |
| * |
| * @throws IllegalStateException if the service reaches a state from which it is not possible to |
| * enter the {@link State#RUNNING} state. e.g. if the {@code state} is |
| * {@code State#TERMINATED} when this method is called then this will throw an |
| * IllegalStateException. |
| * |
| * @since 15.0 |
| */ |
| void awaitRunning(); |
| |
| /** |
| * Waits for the {@link Service} to reach the {@linkplain State#RUNNING running state} for no |
| * more than the given time. |
| * |
| * @param timeout the maximum time to wait |
| * @param unit the time unit of the timeout argument |
| * @throws TimeoutException if the service has not reached the given state within the deadline |
| * @throws IllegalStateException if the service reaches a state from which it is not possible to |
| * enter the {@link State#RUNNING RUNNING} state. e.g. if the {@code state} is |
| * {@code State#TERMINATED} when this method is called then this will throw an |
| * IllegalStateException. |
| * |
| * @since 15.0 |
| */ |
| void awaitRunning(long timeout, TimeUnit unit) throws TimeoutException; |
| |
| /** |
| * Waits for the {@link Service} to reach the {@linkplain State#TERMINATED terminated state}. |
| * |
| * @throws IllegalStateException if the service {@linkplain State#FAILED fails}. |
| * |
| * @since 15.0 |
| */ |
| void awaitTerminated(); |
| |
| /** |
| * Waits for the {@link Service} to reach a terminal state (either |
| * {@link Service.State#TERMINATED terminated} or {@link Service.State#FAILED failed}) for no |
| * more than the given time. |
| * |
| * @param timeout the maximum time to wait |
| * @param unit the time unit of the timeout argument |
| * @throws TimeoutException if the service has not reached the given state within the deadline |
| * @throws IllegalStateException if the service {@linkplain State#FAILED fails}. |
| * @since 15.0 |
| */ |
| void awaitTerminated(long timeout, TimeUnit unit) throws TimeoutException; |
| |
| /** |
| * Returns the {@link Throwable} that caused this service to fail. |
| * |
| * @throws IllegalStateException if this service's state isn't {@linkplain State#FAILED FAILED}. |
| * |
| * @since 14.0 |
| */ |
| Throwable failureCause(); |
| |
| /** |
| * Registers a {@link Listener} to be {@linkplain Executor#execute executed} on the given |
| * executor. The listener will have the corresponding transition method called whenever the |
| * service changes state. The listener will not have previous state changes replayed, so it is |
| * suggested that listeners are added before the service starts. |
| * |
| * <p>{@code addListener} guarantees execution ordering across calls to a given listener but not |
| * across calls to multiple listeners. Specifically, a given listener will have its callbacks |
| * invoked in the same order as the underlying service enters those states. Additionally, at most |
| * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks |
| * may execute concurrently, and listeners may execute in an order different from the one in which |
| * they were registered. |
| * |
| * <p>RuntimeExceptions thrown by a listener will be caught and logged. Any exception thrown |
| * during {@code Executor.execute} (e.g., a {@code RejectedExecutionException}) will be caught and |
| * logged. |
| * |
| * @param listener the listener to run when the service changes state is complete |
| * @param executor the executor in which the listeners callback methods will be run. For fast, |
| * lightweight listeners that would be safe to execute in any thread, consider |
| * {@link MoreExecutors#directExecutor}. |
| * @since 13.0 |
| */ |
| void addListener(Listener listener, Executor executor); |
| |
| /** |
| * The lifecycle states of a service. |
| * |
| * <p>The ordering of the {@link State} enum is defined such that if there is a state transition |
| * from {@code A -> B} then {@code A.compareTo(B} < 0}. N.B. The converse is not true, i.e. if |
| * {@code A.compareTo(B} < 0} then there is <b>not</b> guaranteed to be a valid state transition |
| * {@code A -> B}. |
| * |
| * @since 9.0 (in 1.0 as {@code com.google.common.base.Service.State}) |
| */ |
| @Beta // should come out of Beta when Service does |
| enum State { |
| /** |
| * A service in this state is inactive. It does minimal work and consumes |
| * minimal resources. |
| */ |
| NEW { |
| @Override boolean isTerminal() { |
| return false; |
| } |
| }, |
| |
| /** |
| * A service in this state is transitioning to {@link #RUNNING}. |
| */ |
| STARTING { |
| @Override boolean isTerminal() { |
| return false; |
| } |
| }, |
| |
| /** |
| * A service in this state is operational. |
| */ |
| RUNNING { |
| @Override boolean isTerminal() { |
| return false; |
| } |
| }, |
| |
| /** |
| * A service in this state is transitioning to {@link #TERMINATED}. |
| */ |
| STOPPING { |
| @Override boolean isTerminal() { |
| return false; |
| } |
| }, |
| |
| /** |
| * A service in this state has completed execution normally. It does minimal work and consumes |
| * minimal resources. |
| */ |
| TERMINATED { |
| @Override boolean isTerminal() { |
| return true; |
| } |
| }, |
| |
| /** |
| * A service in this state has encountered a problem and may not be operational. It cannot be |
| * started nor stopped. |
| */ |
| FAILED { |
| @Override boolean isTerminal() { |
| return true; |
| } |
| }; |
| |
| /** Returns true if this state is terminal. */ |
| abstract boolean isTerminal(); |
| } |
| |
| /** |
| * A listener for the various state changes that a {@link Service} goes through in its lifecycle. |
| * |
| * <p>All methods are no-ops by default, implementors should override the ones they care about. |
| * |
| * @author Luke Sandberg |
| * @since 15.0 (present as an interface in 13.0) |
| */ |
| @Beta // should come out of Beta when Service does |
| abstract class Listener { |
| /** |
| * Called when the service transitions from {@linkplain State#NEW NEW} to |
| * {@linkplain State#STARTING STARTING}. This occurs when {@link Service#startAsync} is called |
| * the first time. |
| */ |
| public void starting() {} |
| |
| /** |
| * Called when the service transitions from {@linkplain State#STARTING STARTING} to |
| * {@linkplain State#RUNNING RUNNING}. This occurs when a service has successfully started. |
| */ |
| public void running() {} |
| |
| /** |
| * Called when the service transitions to the {@linkplain State#STOPPING STOPPING} state. The |
| * only valid values for {@code from} are {@linkplain State#STARTING STARTING} or |
| * {@linkplain State#RUNNING RUNNING}. This occurs when {@link Service#stopAsync} is called. |
| * |
| * @param from The previous state that is being transitioned from. |
| */ |
| public void stopping(State from) {} |
| |
| /** |
| * Called when the service transitions to the {@linkplain State#TERMINATED TERMINATED} state. |
| * The {@linkplain State#TERMINATED TERMINATED} state is a terminal state in the transition |
| * diagram. Therefore, if this method is called, no other methods will be called on the |
| * {@link Listener}. |
| * |
| * @param from The previous state that is being transitioned from. The only valid values for |
| * this are {@linkplain State#NEW NEW}, {@linkplain State#RUNNING RUNNING} or |
| * {@linkplain State#STOPPING STOPPING}. |
| */ |
| public void terminated(State from) {} |
| |
| /** |
| * Called when the service transitions to the {@linkplain State#FAILED FAILED} state. The |
| * {@linkplain State#FAILED FAILED} state is a terminal state in the transition diagram. |
| * Therefore, if this method is called, no other methods will be called on the {@link Listener}. |
| * |
| * @param from The previous state that is being transitioned from. Failure can occur in any |
| * state with the exception of {@linkplain State#NEW NEW} or |
| * {@linkplain State#TERMINATED TERMINATED}. |
| * @param failure The exception that caused the failure. |
| */ |
| public void failed(State from, Throwable failure) {} |
| } |
| } |