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/*
* ContractMaintainer.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 static java.util.concurrent.TimeUnit.MILLISECONDS;
/**
* The <code>ContractMaintainer</code> is used provide a controller
* uses a cleaner. This simple delegates to the cleaner queue when
* a renewal is required. Renewals are performed by revoking the
* contract and then reissuing it. This will ensure that the delay
* for expiry of the contract is reestablished within the queue.
*
* @author Niall Gallagher
*
* @see org.simpleframework.common.lease.LeaseCleaner
*/
class ContractMaintainer<T> implements ContractController<T> {
/**
* The queue that is used to issue and revoke contracts.
*/
private final LeaseCleaner<T> queue;
/**
* Constructor for the <code>ContractMaintainer</code> object. This
* is used to create a controller for contracts which will ensure
* that the lease expiry durations are met. All notifications of
* expiry will be delivered to the provided cleaner instance.
*
* @param cleaner this is used to receive expiry notifications
*/
public ContractMaintainer(Cleaner<T> cleaner) {
this.queue = new LeaseCleaner<T>(cleaner);
}
/**
* This method will establish a contract for the given duration.
* If the contract duration expires before it is renewed then a
* notification is sent, typically to a <code>Cleaner</code> to
* to signify that the resource should be released. The contract
* can also be cancelled by providing a zero length duration.
*
* @param contract a contract representing a leased resource
*/
public synchronized void issue(Contract<T> contract) {
queue.issue(contract);
}
/**
* This ensures that the contract is renewed for the duration on
* the contract, which may have changed since it was issued or
* last renewed. If the duration on the contract has changed this
* will insure the previous contract duration is revoked and the
* new duration is used to maintain the leased resource.
*
* @param contract a contract representing a leased resource
*/
public synchronized void renew(Contract<T> contract) {
boolean active = queue.revoke(contract);
if(!active) {
throw new LeaseException("Lease has expired for " + contract);
}
queue.issue(contract);
}
/**
* 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.
*
* @param contract a contract representing a leased resource
*/
public synchronized void cancel(Contract<T> contract) {
boolean active = queue.revoke(contract);
if(!active) {
throw new LeaseException("Lease has expired for " + contract);
}
contract.setDelay(0, MILLISECONDS);
queue.issue(contract);
}
/**
* This method is used to cancel all outstanding leases and to
* close the controller. Closing the controller ensures that it
* can no longer be used to issue or renew leases. All resources
* occupied by the controller are released, including threads,
* memory, and all leased resources occupied by the instance.
*
* @throws LeaseException if the controller can not be closed
*/
public synchronized void close() {
queue.close();
}
}
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