simplesemaphore.java

非常好用的计划任务调度包,能定义复杂的任务

/*
 * Copyright James House (c) 2001-2004
 * 
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met: 1.
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer. 2. Redistributions in
 * binary form must reproduce the above copyright notice, this list of
 * conditions and the following disclaimer in the documentation and/or other
 * materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *  
 */
package org.quartz.impl.jdbcjobstore;

import java.sql.Connection;
import java.util.HashSet;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * 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 class SimpleSemaphore implements Semaphore {

    /*
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     * 
     * Data members.
     * 
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     */

    ThreadLocal lockOwners = new ThreadLocal();

    HashSet locks = new HashSet();

    /*
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     * 
     * Interface.
     * 
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     */

    Log getLog() {
        return LogFactory.getLog(getClass());
        //return LogFactory.getLog("LOCK:"+Thread.currentThread().getName());
    }

    private HashSet getThreadLocks() {
        HashSet threadLocks = (HashSet) lockOwners.get();
        if (threadLocks == null) {
            threadLocks = new HashSet();
            lockOwners.set(threadLocks);
        }
        return threadLocks;
    }

    /**
     * Grants a lock on the identified resource to the calling thread (blocking
     * until it is available).
     * 
     * @return true if the lock was obtained.
     */
    public synchronized boolean obtainLock(Connection conn, String lockName) {

        lockName = lockName.intern();

        Log log = getLog();

        if(log.isDebugEnabled())
            log.debug(
                "Lock '" + lockName + "' is desired by: "
                        + Thread.currentThread().getName());

        if (!isLockOwner(conn, lockName)) {
            if(log.isDebugEnabled())
                log.debug(
                    "Lock '" + lockName + "' is being obtained: "
                            + Thread.currentThread().getName());
            while (locks.contains(lockName)) {
                try {
                    this.wait();
                } catch (InterruptedException ie) {
                    if(log.isDebugEnabled())
                        log.debug(
                            "Lock '" + lockName + "' was not obtained by: "
                                    + Thread.currentThread().getName());
                }
            }

            if(log.isDebugEnabled())
                log.debug(
                    "Lock '" + lockName + "' given to: "
                            + Thread.currentThread().getName());
            getThreadLocks().add(lockName);
            locks.add(lockName);
        } else
            if(log.isDebugEnabled())
                log.debug(
                    "Lock '" + lockName + "' already owned by: "
                            + Thread.currentThread().getName()
                            + " -- but not owner!",
                    new Exception("stack-trace of wrongful returner"));

        return true;
    }

    /**
     * Release the lock on the identified resource if it is held by the calling
     * thread.
     */
    public synchronized void releaseLock(Connection conn, String lockName) {

        lockName = lockName.intern();

        if (isLockOwner(conn, lockName)) {
            if(getLog().isDebugEnabled())
                getLog().debug(
                    "Lock '" + lockName + "' retuned by: "
                            + Thread.currentThread().getName());
            getThreadLocks().remove(lockName);
            locks.remove(lockName);
            this.notify();
        } else
            if(getLog().isDebugEnabled())
                getLog().debug(
                    "Lock '" + lockName + "' attempt to retun by: "
                            + Thread.currentThread().getName()
                            + " -- but not owner!",
                    new Exception("stack-trace of wrongful returner"));
    }

    /**
     * Determine whether the calling thread owns a lock on the identified
     * resource.
     */
    public synchronized boolean isLockOwner(Connection conn, String lockName) {

        lockName = lockName.intern();

        return getThreadLocks().contains(lockName);
    }

    public void init(Connection conn, List listOfLocks) {
        // nothing to do...
    }

}