// =================================================================================================
// Copyright 2011 Twitter, Inc.
// -------------------------------------------------------------------------------------------------
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this work except in compliance with the License.
// You may obtain a copy of the License in the LICENSE file, or 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.twitter.common.net.pool;
import com.google.common.collect.ImmutableSet;
/**
* A host set that can be monitored for changes.
*
* @param <T> The type that is used to identify members of the host set.
*
* @author William Farner
*/
public interface DynamicHostSet<T> {
/**
* Registers a monitor to receive change notices for this server set as long as this jvm process
* is alive. Blocks until the initial server set can be gathered and delivered to the monitor.
* The monitor will be notified if the membership set or parameters of existing members have
* changed.
*
* @param monitor the server set monitor to call back when the host set changes
* @throws MonitorException if there is a problem monitoring the host set
*/
public void monitor(final HostChangeMonitor<T> monitor) throws MonitorException;
/**
* An interface to an object that is interested in receiving notification whenever the host set
* changes.
*/
public static interface HostChangeMonitor<T> {
/**
* Called when either the available set of services changes (when a service dies or a new
* instance comes on-line) or when an existing service advertises a status or health change.
*
* @param hostSet the current set of available ServiceInstances
*/
void onChange(ImmutableSet<T> hostSet);
}
public static class MonitorException extends Exception {
public MonitorException(String msg) {
super(msg);
}
public MonitorException(String msg, Throwable cause) {
super(msg, cause);
}
}
}