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/*
* Lease.java May 2004
*
* Copyright (C) 2004, Niall Gallagher <niallg@users.sf.net>
*
* 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.simpleframework.common.lease;
import java.util.concurrent.TimeUnit;
/**
* The <code>Lease</code> object is used to keep a keyed resource
* active. This provides a very simple lease that can be used to
* track the activity of a resource or system. Keeping track of
* activity allows resources to be maintained until such time
* that they are no longer required, allowing the server to clean
* up any allocated memory, file descriptors, or other such data.
*
* @author Niall Gallagher
*/
public interface Lease<T> {
/**
* Determines the duration remaining before the lease expires.
* The expiry is given as the number of <code>TimeUnit</code>
* seconds remaining before the lease expires. If this value is
* negative it should be assumed that the lease has expired.
*
* @param unit this is the time unit used for the duration
*
* @return the duration remaining within this lease instance
*
* @exception Exception if the expiry could not be acquired
*/
long getExpiry(TimeUnit unit) throws LeaseException;
/**
* This ensures that the leased resource is maintained for the
* specified number of <code>TimeUnit</code> seconds. Allowing
* the duration unit to be specified enables the lease system
* to maintain a resource with a high degree of accuracy. The
* accuracy of the leasing system is dependent on how long it
* takes to clean the resource associated with the lease.
*
* @param duration this is the length of time to renew for
* @param unit this is the time unit used for the duration
*
* @exception Exception if the lease could not be renewed
*/
void renew(long duration, TimeUnit unit) throws LeaseException;
/**
* This will cancel the lease and release the resource. This
* has the same effect as the <code>renew</code> method with
* a zero length duration. Once this has been called the
* <code>Cleaner</code> used should be notified immediately.
* If the lease has already expired this throws an exception.
*
* @exception Exception if the expiry has been passed
*/
void cancel() throws LeaseException;
/**
* Provides the key for the resource that this lease represents.
* This can be used to identify the resource should the need
* arise. Also, this provides a convenient means of identifying
* leases when using or storing it as an <code>Object</code>.
*
* @return this returns the key for the resource represented
*/
T getKey();
}
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