/*
* JBoss, the OpenSource J2EE webOS
*
* Distributable under LGPL license.
* See terms of license at gnu.org.
*/
package org.jboss.cache.lock;
import EDU.oswego.cs.dl.util.concurrent.FIFOSemaphore;
import EDU.oswego.cs.dl.util.concurrent.NullSync;
import EDU.oswego.cs.dl.util.concurrent.Sync;
/**
* Transaction isolation level of READ-UNCOMMITTED. Reads always succeed (NullLock), whereas writes are exclusive.
* It prevents none of the dirty read, non-repeatable read, or phantom read.
*
* @author Ben Wang
* @version $Revision: 2073 $
*/
public class LockStrategyReadUncommitted implements LockStrategy
{
private FIFOSemaphore wLock_;
private NullSync rLock_; // Null lock will always return true
public LockStrategyReadUncommitted()
{
wLock_ = new FIFOSemaphore(1);
rLock_ = new NullSync();
}
/**
* @see org.jboss.cache.lock.LockStrategy#readLock()
*/
public Sync readLock()
{
return rLock_;
}
/**
* @see org.jboss.cache.lock.LockStrategy#upgradeLockAttempt(long)
*/
public Sync upgradeLockAttempt(long msecs) throws UpgradeException
{
// Since write is exclusive, we need to obtain the write lock first
// before we can return the upgrade
try {
wLock_.attempt(msecs);
} catch (InterruptedException e) {
throw new UpgradeException("Upgrade failed in " + msecs + " msecs", e);
}
return wLock_;
}
/**
* @see org.jboss.cache.lock.LockStrategy#writeLock()
*/
public Sync writeLock()
{
return wLock_;
}
}