org.apache.hadoop.service.Service Maven / Gradle / Ivy
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.hadoop.service;
import org.apache.hadoop.classification.InterfaceAudience.Public;
import org.apache.hadoop.classification.InterfaceStability.Evolving;
import org.apache.hadoop.conf.Configuration;
import java.io.Closeable;
import java.io.IOException;
import java.util.List;
import java.util.Map;
/**
* Service LifeCycle.
*/
@Public
@Evolving
public interface Service extends Closeable {
/**
* Service states
*/
public enum STATE {
/** Constructed but not initialized */
NOTINITED(0, "NOTINITED"),
/** Initialized but not started or stopped */
INITED(1, "INITED"),
/** started and not stopped */
STARTED(2, "STARTED"),
/** stopped. No further state transitions are permitted */
STOPPED(3, "STOPPED");
/**
* An integer value for use in array lookup and JMX interfaces.
* Although {@link Enum#ordinal()} could do this, explicitly
* identify the numbers gives more stability guarantees over time.
*/
private final int value;
/**
* A name of the state that can be used in messages
*/
private final String statename;
private STATE(int value, String name) {
this.value = value;
this.statename = name;
}
/**
* Get the integer value of a state
* @return the numeric value of the state
*/
public int getValue() {
return value;
}
/**
* Get the name of a state
* @return the state's name
*/
@Override
public String toString() {
return statename;
}
}
/**
* Initialize the service.
*
* The transition MUST be from {@link STATE#NOTINITED} to {@link STATE#INITED}
* unless the operation failed and an exception was raised, in which case
* {@link #stop()} MUST be invoked and the service enter the state
* {@link STATE#STOPPED}.
* @param config the configuration of the service
* @throws RuntimeException on any failure during the operation
*/
void init(Configuration config);
/**
* Start the service.
*
* The transition MUST be from {@link STATE#INITED} to {@link STATE#STARTED}
* unless the operation failed and an exception was raised, in which case
* {@link #stop()} MUST be invoked and the service enter the state
* {@link STATE#STOPPED}.
* @throws RuntimeException on any failure during the operation
*/
void start();
/**
* Stop the service. This MUST be a no-op if the service is already
* in the {@link STATE#STOPPED} state. It SHOULD be a best-effort attempt
* to stop all parts of the service.
*
* The implementation must be designed to complete regardless of the service
* state, including the initialized/uninitialized state of all its internal
* fields.
* @throws RuntimeException on any failure during the stop operation
*/
void stop();
/**
* A version of stop() that is designed to be usable in Java7 closure
* clauses.
* Implementation classes MUST relay this directly to {@link #stop()}
* @throws IOException never
* @throws RuntimeException on any failure during the stop operation
*/
void close() throws IOException;
/**
* Register a listener to the service state change events.
* If the supplied listener is already listening to this service,
* this method is a no-op.
* @param listener a new listener
*/
void registerServiceListener(ServiceStateChangeListener listener);
/**
* Unregister a previously registered listener of the service state
* change events. No-op if the listener is already unregistered.
* @param listener the listener to unregister.
*/
void unregisterServiceListener(ServiceStateChangeListener listener);
/**
* Get the name of this service.
* @return the service name
*/
String getName();
/**
* Get the configuration of this service.
* This is normally not a clone and may be manipulated, though there are no
* guarantees as to what the consequences of such actions may be
* @return the current configuration, unless a specific implentation chooses
* otherwise.
*/
Configuration getConfig();
/**
* Get the current service state
* @return the state of the service
*/
STATE getServiceState();
/**
* Get the service start time
* @return the start time of the service. This will be zero if the service
* has not yet been started.
*/
long getStartTime();
/**
* Query to see if the service is in a specific state.
* In a multi-threaded system, the state may not hold for very long.
* @param state the expected state
* @return true if, at the time of invocation, the service was in that state.
*/
boolean isInState(STATE state);
/**
* Get the first exception raised during the service failure. If null,
* no exception was logged
* @return the failure logged during a transition to the stopped state
*/
Throwable getFailureCause();
/**
* Get the state in which the failure in {@link #getFailureCause()} occurred.
* @return the state or null if there was no failure
*/
STATE getFailureState();
/**
* Block waiting for the service to stop; uses the termination notification
* object to do so.
*
* This method will only return after all the service stop actions
* have been executed (to success or failure), or the timeout elapsed
* This method can be called before the service is inited or started; this is
* to eliminate any race condition with the service stopping before
* this event occurs.
* @param timeout timeout in milliseconds. A value of zero means "forever"
* @return true iff the service stopped in the time period
*/
boolean waitForServiceToStop(long timeout);
/**
* Get a snapshot of the lifecycle history; it is a static list
* @return a possibly empty but never null list of lifecycle events.
*/
public List getLifecycleHistory();
/**
* Get the blockers on a service -remote dependencies
* that are stopping the service from being live.
* @return a (snapshotted) map of blocker name->description values
*/
public Map getBlockers();
}