org.quartz.impl.jdbcjobstore.SimpleSemaphore Maven / Gradle / Ivy
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SDK for dev_appserver (local development) with some of the dependencies shaded (repackaged)
/*
* 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;
import java.util.HashSet;
import java.util.List;
import com.google.appengine.repackaged.org.apache.commons.logging.Log;
import com.google.appengine.repackaged.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...
}
}