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/*******************************************************************************
* Copyright (c) 2003, 2013 IBM Corporation and others.
*
* This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-2.0/
*
* SPDX-License-Identifier: EPL-2.0
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.osgi.internal.serviceregistry;
import org.eclipse.osgi.internal.framework.BundleContextImpl;
import org.eclipse.osgi.internal.messages.Msg;
import org.osgi.framework.ServiceException;
/**
* This class represents the use of a service by a bundle. One is created for each
* service acquired by a bundle.
*
* <p>
* This class manages a singleton service.
*
* @ThreadSafe
*/
public class ServiceUse<S> {
/** ServiceDescription of the registered service */
final ServiceRegistrationImpl<S> registration;
/** bundle's use count for this service */
/* @GuardedBy("this") */
private int useCount;
/**
* Constructs a service use encapsulating the service object.
*
* @param context bundle getting the service
* @param registration ServiceRegistration of the service
*/
ServiceUse(BundleContextImpl context, ServiceRegistrationImpl<S> registration) {
this.useCount = 0;
this.registration = registration;
}
/**
* Get a service's service object and increment the use count.
*
* @return The service object.
*/
/* @GuardedBy("this") */
S getService() {
assert Thread.holdsLock(this);
incrementUse();
return registration.getServiceObject();
}
/**
* Unget a service's service object.
*
* <p>
* Decrements the use count if the service was being used.
*
* @return true if the service was ungotten; otherwise false.
*/
/* @GuardedBy("this") */
boolean ungetService() {
assert Thread.holdsLock(this);
if (!inUse()) {
return false;
}
decrementUse();
return true;
}
/**
* Return the service object for this service use.
*
* @return The service object.
*/
/* @GuardedBy("this") */
S getCachedService() {
return registration.getServiceObject();
}
/**
* Get a new service object for the service.
*
* <p>
* By default, this returns the result of {@link #getService()}.
*
* @return The service object.
*/
/* @GuardedBy("this") */
S newServiceObject() {
return getService();
}
/**
* Release a service object for the service.
*
* <p>
* By default, this returns the result of {@link #ungetService()}.
*
* @param service The service object to release.
* @return true if the service was released; otherwise false.
* @throws IllegalArgumentException If the specified service was not
* provided by this object.
*/
/* @GuardedBy("this") */
boolean releaseServiceObject(final S service) {
if ((service == null) || (service != getCachedService())) {
throw new IllegalArgumentException(Msg.SERVICE_OBJECTS_UNGET_ARGUMENT_EXCEPTION);
}
return ungetService();
}
/**
* Release all uses of the service and reset the use count to zero.
*/
/* @GuardedBy("this") */
void release() {
assert Thread.holdsLock(this);
resetUse();
}
/**
* Is this service use using any services?
*
* @return true if no services are being used and this service use can be discarded.
*/
/* @GuardedBy("this") */
boolean isEmpty() {
assert Thread.holdsLock(this);
return !inUse();
}
/**
* Is the use count non zero?
*
* @return true if the use count is greater than zero.
*/
/* @GuardedBy("this") */
boolean inUse() {
return useCount > 0;
}
/**
* Incrementing the use count.
*/
/* @GuardedBy("this") */
void incrementUse() {
if (useCount == Integer.MAX_VALUE) {
throw new ServiceException(Msg.SERVICE_USE_OVERFLOW);
}
useCount++;
}
/**
* Decrementing the use count.
*/
/* @GuardedBy("this") */
void decrementUse() {
assert inUse();
useCount--;
}
/**
* Reset the use count to zero.
*/
/* @GuardedBy("this") */
void resetUse() {
useCount = 0;
}
}
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