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/*
* Copyright 2006 The Apache Software Foundation
*
* 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 org.apache.felix.dependencymanager;
/**
* Generic dependency for a service. A dependency can be required or not.
* A dependency will be activated by the service it belongs to. The service
* will call the <code>start(Service service)</code> and
* <code>stop(Service service)</code> methods.
*
* After it has been started, a dependency must callback
* the associated service's <code>dependencyAvailable()</code> and
* <code>dependencyUnavailable()</code>
* methods. State changes of the dependency itself may only be made as long as
* the dependency is not 'active', meaning it is associated with a running service.
*
* @author <a href="mailto:felix-dev@incubator.apache.org">Felix Project Team</a>
*/
public interface Dependency {
/**
* Returns <code>true</code> if this a required dependency. Required dependencies
* are dependencies that must be available before the service can be activated.
*
* @return <code>true</code> if the dependency is required
*/
public boolean isRequired();
/**
* Returns <code>true</code> if the dependency is available.
*
* @return <code>true</code> if the dependency is available
*/
public boolean isAvailable();
/**
* Starts tracking the dependency. This activates some implementation
* specific mechanism to do the actual tracking. If the tracking discovers
* that the dependency becomes available, it should call
* <code>dependencyAvailable()</code> on the service.
*
* @param service the service that is associated with this dependency
*/
public void start(Service service);
/**
* Stops tracking the dependency. This deactivates the tracking. If the
* dependency was available, the tracker should call
* <code>dependencyUnavaible()</code> before stopping itself to ensure
* that dependencies that aren't "active" are unavailable.
*/
public void stop(Service service);
}