/*  * Copyright 2004-2005 OpenSymphony  *  * 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. *  *//* * Previously Copyright (c) 2001-2004 James House */package org.quartz.impl.jdbcjobstore;import java.sql.Connection;/** * An interface for providing thread/resource locking in order to protect * resources from being altered by multiple threads at the same time. *  * @author jhouse */public interface Semaphore {    /*     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~     *      * Interface.     *      * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~     */    /**     * Grants a lock on the identified resource to the calling thread (blocking     * until it is available).     *      * @param conn Database connection used to establish lock.  Can be null if     * <code>{@link #requiresConnection()}</code> returns false.     *      * @return true if the lock was obtained.     */    boolean obtainLock(Connection conn, String lockName) throws LockException;    /**     * Release the lock on the identified resource if it is held by the calling     * thread.     * @param conn Database connection used to establish lock.  Can be null if     * <code>{@link #requiresConnection()}</code> returns false.     */    void releaseLock(Connection conn, String lockName) throws LockException;    /**     * Determine whether the calling thread owns a lock on the identified     * resource.     * @param conn Database connection used to establish lock.  Can be null if     * <code>{@link #requiresConnection()}</code> returns false.     */    boolean isLockOwner(Connection conn, String lockName) throws LockException;    /**     * Whether this Semaphore implementation requires a database connection for     * its lock management operations.     *      * @see #isLockOwner(Connection, String)     * @see #obtainLock(Connection, String)     * @see #releaseLock(Connection, String)     */    boolean requiresConnection();}