com.google.common.base.Service Maven / Gradle / Ivy
/*
* Copyright (C) 2009 Google Inc.
*
* 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.base;
import com.google.common.annotations.Beta;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
/**
* An object with an operational state, plus asynchronous {@link #start()} and
* {@link #stop()} lifecycle methods to transfer into and out of this state.
* Example services include webservers, RPC servers and timers. The normal
* lifecycle of a service is:
*
* - {@link State#NEW} ->
* - {@link State#STARTING} ->
* - {@link State#RUNNING} ->
* - {@link State#STOPPING} ->
* - {@link State#TERMINATED}
*
*
* If the service fails while starting, running or stopping, its state will be
* {@link State#FAILED}, and its behavior is undefined. Such a service cannot be
* started nor stopped.
*
* Implementors of this interface are strongly encouraged to extend {@link
* com.google.common.util.concurrent.AbstractService} or {@link
* com.google.common.util.concurrent.AbstractExecutionThreadService}, which make
* the threading and state management easier.
*
* @author Jesse Wilson
* @since 1
*/
@Beta // TODO: make it an abstract class and move to common.util.concurrent
public interface Service {
/**
* If the service state is {@link State#NEW}, this initiates service startup
* and returns immediately. If the service has already been started, this
* method returns immediately without taking action. A stopped service may not
* be restarted.
*
* @return a future for the startup result, regardless of whether this call
* initiated startup. Calling {@link Future#get} will block until the
* service has finished starting, and returns one of {@link
* State#RUNNING}, {@link State#STOPPING} or {@link State#TERMINATED}. If
* the service fails to start, {@link Future#get} will throw an {@link
* ExecutionException}, and the service's state will be {@link
* State#FAILED}. If it has already finished starting, {@link Future#get}
* returns immediately. Cancelling the returned future is unsupported and
* always returns {@code false}.
*/
Future start();
/**
* Initiates service startup (if necessary), returning once the service has
* finished starting. Unlike calling {@code start().get()}, this method throws
* no checked exceptions.
*
* @throws InterruptedRuntimeException if the thread was interrupted while
* waiting for the service to finish starting up.
* @throws RuntimeException if startup failed
* @return the state of the service when startup finished.
*/
State startAndWait();
/**
* Returns {@code true} if this service is {@link State#RUNNING running}.
*/
boolean isRunning();
/**
* Returns the lifecycle state of the service.
*/
State state();
/**
* If the service is {@link State#STARTING} or {@link State#RUNNING}, this
* initiates service shutdown and returns immediately. If this is {@link
* State#NEW}, it is {@link State#TERMINATED terminated} without having been
* started nor stopped. If the service has already been stopped, this
* method returns immediately without taking action.
*
* @return a future for the shutdown result, regardless of whether this call
* initiated shutdown. Calling {@link Future#get} will block until the
* service has finished shutting down, and either returns {@link
* State#TERMINATED} or throws an {@link ExecutionException}. If it has
* already finished stopping, {@link Future#get} returns immediately.
* Cancelling this future is unsupported and always returns {@code
* false}.
*/
Future stop();
/**
* Initiates service shutdown (if necessary), returning once the service has
* finished stopping. If this is {@link State#STARTING}, startup will be
* cancelled. If this is {@link State#NEW}, it is {@link State#TERMINATED
* terminated} without having been started nor stopped. Unlike calling {@code
* stop().get()}, this method throws no checked exceptions.
*
* @throws InterruptedRuntimeException if the thread was interrupted while
* waiting for the service to finish shutting down.
* @throws RuntimeException if shutdown failed
* @return the state of the service when shutdown finished.
*/
State stopAndWait();
/**
* The lifecycle states of a service.
*/
public enum State {
/**
* A service in this state is inactive. It does minimal work and consumes
* minimal resources.
*/
NEW,
/**
* A service in this state is transitioning to {@link #RUNNING}.
*/
STARTING,
/**
* A service in this state is operational.
*/
RUNNING,
/**
* A service in this state is transitioning to {@link #TERMINATED}.
*/
STOPPING,
/**
* A service in this state has completed execution normally. It does minimal
* work and consumes minimal resources.
*/
TERMINATED,
/**
* A service in this state has encountered a problem and may not be
* operational. It cannot be started nor stopped.
*/
FAILED
}
}