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/*
* Copyright (c) OSGi Alliance (2012, 2016). All Rights Reserved.
*
* 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.osgi.framework;
import org.osgi.annotation.versioning.ProviderType;
/**
* Allows multiple service objects for a service to be obtained.
* <p>
* For services with {@link Constants#SCOPE_PROTOTYPE prototype} scope, multiple
* service objects for the service can be obtained. Since implementations of
* {@link PrototypeServiceFactory} can return the same service object
* repeatedly, the framework must use count the returned service objects to
* release the service object only when its use count returns to zero.
* <p>
* For services with {@link Constants#SCOPE_SINGLETON singleton} or
* {@link Constants#SCOPE_BUNDLE bundle} scope, only one, use-counted service
* object is available to a requesting bundle.
* <p>
* Any unreleased service objects obtained from this {@code ServiceObjects}
* object are automatically released by the framework when the bundle associated
* with the BundleContext used to create this {@code ServiceObjects} object is
* stopped.
*
* @param <S> Type of Service
* @see BundleContext#getServiceObjects(ServiceReference)
* @see PrototypeServiceFactory
* @ThreadSafe
* @since 1.8
* @author $Id$
*/
@ProviderType
public interface ServiceObjects<S> {
/**
* Returns a service object for the {@link #getServiceReference()
* associated} service.
* <p>
* This {@code ServiceObjects} object can be used to obtain multiple service
* objects for the associated service if the service has
* {@link Constants#SCOPE_PROTOTYPE prototype} scope.
* <p>
* If the associated service has {@link Constants#SCOPE_SINGLETON singleton}
* or {@link Constants#SCOPE_BUNDLE bundle} scope, this method behaves the
* same as calling the {@link BundleContext#getService(ServiceReference)}
* method for the associated service. That is, only one, use-counted service
* object is available from this {@link ServiceObjects} object.
* <p>
* This method will always return {@code null} when the associated service
* has been unregistered.
* <p>
* For a prototype scope service, the following steps are required to obtain
* a service object:
* <ol>
* <li>If the associated service has been unregistered, {@code null} is
* returned.</li>
* <li>The
* {@link PrototypeServiceFactory#getService(Bundle, ServiceRegistration)}
* method is called to supply a customized service object for the caller.
* </li>
* <li>If the service object returned by the {@code PrototypeServiceFactory}
* object is {@code null}, not an {@code instanceof} all the classes named
* when the service was registered or the {@code PrototypeServiceFactory}
* object throws an exception, {@code null} is returned and a Framework
* event of type {@link FrameworkEvent#ERROR} containing a
* {@link ServiceException} describing the error is fired.</li>
* <li>The use count for the customized service object is incremented by
* one.</li>
* <li>The customized service object is returned.</li>
* </ol>
*
* @return A service object for the associated service or {@code null} if
* the service is not registered, the customized service object
* returned by a {@code ServiceFactory} does not implement the
* classes under which it was registered or the
* {@code ServiceFactory} threw an exception.
* @throws IllegalStateException If the BundleContext used to create this
* {@code ServiceObjects} object is no longer valid.
* @see #ungetService(Object)
*/
public S getService();
/**
* Releases a service object for the {@link #getServiceReference()
* associated} service.
* <p>
* This {@code ServiceObjects} object can be used to obtain multiple service
* objects for the associated service if the service has
* {@link Constants#SCOPE_PROTOTYPE prototype} scope. If the associated
* service has {@link Constants#SCOPE_SINGLETON singleton} or
* {@link Constants#SCOPE_BUNDLE bundle} scope, this method behaves the same
* as calling the {@link BundleContext#ungetService(ServiceReference)}
* method for the associated service. That is, only one, use-counted service
* object is available from this {@link ServiceObjects} object.
* <p>
* For a prototype scope service, the following steps are required to
* release a service object:
* <ol>
* <li>If the associated service has been unregistered, this method returns
* without doing anything.</li>
* <li>The use count for the specified service object is decremented by one.
* </li>
* <li>If the use count for the specified service object is now zero, the
* {@link PrototypeServiceFactory#ungetService(Bundle, ServiceRegistration, Object)}
* method is called to release the specified service object.</li>
* </ol>
* <p>
* The specified service object must no longer be used and all references to
* it should be destroyed after calling this method when the use count has
* returned to zero.
*
* @param service A service object previously provided by this
* {@code ServiceObjects} object.
* @throws IllegalStateException If the BundleContext used to create this
* {@code ServiceObjects} object is no longer valid.
* @throws IllegalArgumentException If the specified service object is
* {@code null} or was not provided by a {@code ServiceObjects}
* object for the associated service.
* @see #getService()
*/
public void ungetService(S service);
/**
* Returns the {@link ServiceReference} for the service associated with this
* {@code ServiceObjects} object.
*
* @return The {@link ServiceReference} for the service associated with this
* {@code ServiceObjects} object.
*/
public ServiceReference<S> getServiceReference();
}
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