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The Broker Discovery module for QpidJMS
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/*
 * 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.qpid.jms.provider.discovery;

import java.util.concurrent.ScheduledExecutorService;

import org.apache.qpid.jms.provider.ProviderException;

/**
 * Interface for all agents used to detect instances of remote peers on the network.
 */
public interface DiscoveryAgent {

    /**
     * Indicates if this DiscoveryAgent requires a ScheduledExecutorService in order
     * to perform its discovery work.
     *
     * @return true if the agent requires that its parent provide it with a scheduler.
     */
    boolean isSchedulerRequired();

    /**
     * Provider a ScheduledExecutorService to the DiscoveryAgent that requires a
     * scheduler to perform its discovery work.  If the agent performs long polling
     * style operations such as a socket read then it should not use the provided
     * scheduler as that could block other agents from performing their own work.
     *
     * @param scheduler
     *        An initialized Scheduler service that this agent can use for its work.
     */
    void setScheduler(ScheduledExecutorService scheduler);

    /**
     * Sets the discovery listener
     *
     * @param listener
     *        the listener to notify on discovery events, or null to clear.
     */
    void setDiscoveryListener(DiscoveryListener listener);

    /**
     * Starts the agent after which new remote peers can start to be found.
     *
     * @throws ProviderException if an IO error occurs while starting the agent.
     * @throws IllegalStateException if the agent is not properly configured.
     */
    void start() throws ProviderException, IllegalStateException;

    /**
     * Stops the agent after which no new remote peers will be found.  This
     * method should attempt to close any agent resources and if an error occurs
     * it should handle it and not re-throw to the calling entity.
     */
    void close();

    /**
     * Suspends the Agent which suppresses any new attempts to discover remote
     * peers until the agent is resumed.  If the service is not able to be suspended
     * then this method should not throw an Exception, simply return as if successful.
     */
    void suspend();

    /**
     * Resumes discovery by this agent if it was previously suspended.  If the agent
     * does not support being suspended or is closed this method should simply return
     * without throwing any exceptions.
     */
    void resume();

}