ContractLease.java

/*
 * ContractLease.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.util.lease;

import java.util.concurrent.TimeUnit;

/**
 * The <code>ContractLease</code> is used to maintain contracts by using a
 * controller object. This will invoke the controller with the contract when a
 * lease operation is performed. A lease is renewed by changing the contract
 * duration and passing that to the controller which will reestablish the expiry
 * time for it.
 * 
 * @author Niall Gallagher
 */
class ContractLease<T> implements Lease<T> {

    /**
     * This is the controller object used to handle contracts.
     */
    private final Controller<T> handler;

    /**
     * This is the contract object representing the lease.
     */
    private final Contract<T> contract;

    /**
     * Constructor for the <code>ContractLease</code> object. This is used to
     * create a lease which will maintain a contract using a controller object.
     * Lease renewals are performed by changing the expiry duration on the
     * contract and notifying the controller.
     * 
     * @param handler
     *            this is used to manage the contract expiration
     * @param contract
     *            this is the contract representing the lease
     */
    public ContractLease(Controller<T> handler, Contract<T> contract) {
        this.handler = handler;
        this.contract = contract;
    }

    /**
     * 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 LeaseException
     *                if the lease expiry has passed
     */
    @Override
    public long getExpiry(TimeUnit unit) throws LeaseException {
        return this.contract.getDelay(unit);
    }

    /**
     * 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 dependant 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 LeaseException
     *                if the expiry has been passed
     */
    @Override
    public void renew(long duration, TimeUnit unit) throws LeaseException {
        if (duration >= 0) {
            this.contract.setDelay(duration, unit);
        }
        this.handler.renew(this.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.
     * 
     * @exception LeaseException
     *                if the expiry has been passed
     */
    @Override
    public void cancel() throws LeaseException {
        this.handler.cancel(this.contract);
    }

    /**
     * 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
     */
    @Override
    public T getKey() {
        return this.contract.getKey();
    }
}