/**
* 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.metrics2;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* The metrics system interface
*/
@InterfaceAudience.Public
@InterfaceStability.Evolving
public abstract class MetricsSystem implements MetricsSystemMXBean {
@InterfaceAudience.Private
public abstract MetricsSystem init(String prefix);
/**
* Register a metrics source
* @param <T> the actual type of the source object
* @param source object to register
* @param name of the source. Must be unique or null (then extracted from
* the annotations of the source object.)
* @param desc the description of the source (or null. See above.)
* @return the source object
* @exception MetricsException
*/
public abstract <T> T register(String name, String desc, T source);
/**
* Register a metrics source (deriving name and description from the object)
* @param <T> the actual type of the source object
* @param source object to register
* @return the source object
* @exception MetricsException
*/
public <T> T register(T source) {
return register(null, null, source);
}
/**
* @param name of the metrics source
* @return the metrics source (potentially wrapped) object
*/
@InterfaceAudience.Private
public abstract MetricsSource getSource(String name);
/**
* Register a metrics sink
* @param <T> the type of the sink
* @param sink to register
* @param name of the sink. Must be unique.
* @param desc the description of the sink
* @return the sink
* @exception MetricsException
*/
public abstract <T extends MetricsSink>
T register(String name, String desc, T sink);
/**
* Register a callback interface for JMX events
* @param callback the callback object implementing the MBean interface.
*/
public abstract void register(Callback callback);
/**
* Shutdown the metrics system completely (usually during server shutdown.)
* The MetricsSystemMXBean will be unregistered.
* @return true if shutdown completed
*/
public abstract boolean shutdown();
/**
* The metrics system callback interface (needed for proxies.)
*/
public interface Callback {
/**
* Called before start()
*/
void preStart();
/**
* Called after start()
*/
void postStart();
/**
* Called before stop()
*/
void preStop();
/**
* Called after stop()
*/
void postStop();
}
/**
* Convenient abstract class for implementing callback interface
*/
public static abstract class AbstractCallback implements Callback {
@Override public void preStart() {}
@Override public void postStart() {}
@Override public void preStop() {}
@Override public void postStop() {}
}
}