Contract.java

/*
 * Contract.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.Delayed;
import java.util.concurrent.TimeUnit;

/**
 * A <code>Contract</code> is used to represent the contract a lease has been
 * issued. This contains all relevant information regarding the lease, such as
 * the keyed resource that has been leased and the duration of the lease. Delays
 * for the contract can be measured in any <code>TimeUnit</code> for
 * convinienct.
 * 
 * @author Niall Gallagher
 */
interface Contract<T> extends Delayed {

    /**
     * This returns the key for the resource this represents. This is used when
     * the contract has expired to clean resources associated with the lease. It
     * is passed in to the cleaner as an parameter to the callback. The cleaner
     * is then responsible for cleaning any resources associated with the lease.
     * 
     * @return returns the resource key that this represents
     */
    T getKey();

    /**
     * This method will return the number of <code>TimeUnit</code> seconds that
     * remain in the contract. If the value returned is less than or equal to
     * zero then it should be assumed that the lease has expired, if greater
     * than zero the lease is active.
     * 
     * @return returns the duration in time unit remaining
     */
    @Override
    long getDelay(TimeUnit unit);

    /**
     * This method is used to set the number of <code>TimeUnit</code> seconds
     * that should remain within the contract. This is used when the contract is
     * to be reissued. Once a new duration has been set the contract for the
     * lease has been changed and the previous expiry time is ignores, so only
     * one clean is called.
     * 
     * @param delay
     *            this is the delay to be used for this contract
     * @param unit
     *            this is the time unit measurment for the delay
     */
    void setDelay(long delay, TimeUnit unit);

    /**
     * This is used to provide a description of the contract that the instance
     * represents. A description well contain the key owned by the contract as
     * well as the expiry time expected for it. This is used to provide
     * descriptive messages in the exceptions.
     * 
     * @return a descriptive message describing the contract object
     */
    @Override
    String toString();
}