com.arjuna.ats.txoj.Lock Maven / Gradle / Ivy
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/*
* JBoss, Home of Professional Open Source
* Copyright 2006, Red Hat Middleware LLC, and individual contributors
* as indicated by the @author tags.
* See the copyright.txt in the distribution for a
* full listing of individual contributors.
* This copyrighted material is made available to anyone wishing to use,
* modify, copy, or redistribute it subject to the terms and conditions
* of the GNU Lesser General Public License, v. 2.1.
* This program is distributed in the hope that it will be useful, but WITHOUT A
* WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
* PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
* You should have received a copy of the GNU Lesser General Public License,
* v.2.1 along with this distribution; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02110-1301, USA.
*
* (C) 2005-2006,
* @author JBoss Inc.
*/
/*
* Copyright (C) 1998, 1999, 2000,
*
* Arjuna Solutions Limited,
* Newcastle upon Tyne,
* Tyne and Wear,
* UK.
*
* $Id: Lock.java 2342 2006-03-30 13:06:17Z $
*/
package com.arjuna.ats.txoj;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import com.arjuna.ats.arjuna.ObjectType;
import com.arjuna.ats.arjuna.StateManager;
import com.arjuna.ats.arjuna.common.Uid;
import com.arjuna.ats.arjuna.coordinator.ActionHierarchy;
import com.arjuna.ats.arjuna.coordinator.BasicAction;
import com.arjuna.ats.arjuna.state.InputObjectState;
import com.arjuna.ats.arjuna.state.OutputObjectState;
import com.arjuna.ats.arjuna.utils.Utility;
import com.arjuna.ats.txoj.logging.txojLogger;
/**
* Instances of this class (or derived user classes) are used when trying to set
* a lock. The default implementation provides a single-write/multiple-reader
* policy. However, by overridding the appropriate methods, other, type-specific
* concurrency control locks can be implemented.
*
* @author Mark Little ([email protected])
* @version $Id: Lock.java 2342 2006-03-30 13:06:17Z $
* @since JTS 1.0.
*/
public class Lock extends StateManager
{
/**
* Create a new lock.
*/
public Lock()
{
super(ObjectType.NEITHER);
currentStatus = LockStatus.LOCKFREE;
nextLock = null;
lMode = LockMode.WRITE;
owners = new ActionHierarchy(0);
}
/**
* Create a new Lock object and initialise it. Mode is based upon argument.
* The value of BasicAction.Current determines the values of the remainder
* of the fields. If there is no action running the owner field is set to be
* the application uid created when the application starts.
*/
public Lock(int lm)
{
super(ObjectType.NEITHER);
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::Lock(" + lm
+ ")");
}
currentStatus = LockStatus.LOCKFREE;
nextLock = null;
lMode = lm;
owners = new ActionHierarchy(0);
BasicAction curr = BasicAction.Current();
if (curr == null)
{
int currentPid = Utility.getpid(); // ::getpid();
ActionHierarchy ah = new ActionHierarchy(1); /* max depth of 1 */
if (applicUid == null)
{
applicUid = new Uid();
}
if (applicPid != currentPid)
{
/*
* Process id change probably due to a fork(). Get new pid and
* generate a new Applic_Uid
*/
applicPid = currentPid;
applicUid = new Uid();
}
ah.add(applicUid);
owners.copy(ah);
}
else
{
owners.copy(curr.getHierarchy());
}
}
/**
* This is used when re-initialising a Lock after retrieval from the object
* store.
*/
public Lock(Uid storeUid)
{
super(storeUid, ObjectType.NEITHER);
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::Lock("
+ storeUid + ")");
}
currentStatus = LockStatus.LOCKFREE;
nextLock = null;
lMode = LockMode.WRITE;
owners = new ActionHierarchy(0);
}
/**
* General clean up as Lock is deleted.
*/
public void finalize () throws Throwable
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock.finalize()");
}
super.terminate();
owners = null;
super.finalize();
}
/*
* Public utility operations. Most are sufficiently simple as to be self
* explanatory!
*/
/**
* @return the mode this lock is currently in, e.g.,
* LockMode.READ.
*/
public final int getLockMode ()
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::getLockMode()");
}
return lMode;
}
/**
* @return the identity of the lock's current owner (the transaction id).
*/
public final Uid getCurrentOwner ()
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::getCurrentOwner()");
}
return owners.getDeepestActionUid();
}
/**
* @return the transaction hierarchy associated with this lock.
*/
public final ActionHierarchy getAllOwners ()
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::getAllOwners()");
}
return owners;
}
/**
* @return the lock's current status.
*/
public final int getCurrentStatus ()
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::getCurrentStatus()");
}
return currentStatus;
}
/**
* Change the transaction hierarchy associated with the lock to that
* provided.
*/
public final void changeHierarchy (ActionHierarchy newOwner)
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::getCurrentOwner()");
}
owners.copy(newOwner);
if (currentStatus == LockStatus.LOCKFREE)
currentStatus = LockStatus.LOCKHELD;
}
/**
* Propagate the lock.
*/
public final void propagate ()
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::propagate()");
}
owners.forgetDeepest();
currentStatus = LockStatus.LOCKRETAINED;
}
/**
* Does this lock imply a modification of the object it is applied to? For
* example, a READ lock would return false, but a WRITE lock would return
* true.
*
* @return true if this lock implies the object's state will be
* modified, false otherwise.
*/
public boolean modifiesObject ()
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::modifiesObject()");
}
return ((lMode == LockMode.WRITE) ? true : false);
}
/**
* Implementation of Lock conflict check. Returns TRUE if there is conflict
* FALSE otherwise. Does not take account of relationship in the atomic
* action hierarchy since this is a function of LockManager.
*
* @return true if this lock conflicts with the parameter,
* false otherwise.
*/
public boolean conflictsWith (Lock otherLock)
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::conflictsWith(" + otherLock + ")\n" + "\tLock 1:\n"
+ this + "\n" + "\tLock 2:\n" + otherLock);
}
if (!(getCurrentOwner().equals(otherLock.getCurrentOwner())))
{
switch (lMode)
{
case LockMode.WRITE:
return true; /* WRITE conflicts always */
case LockMode.READ:
if (otherLock.getLockMode() != LockMode.READ)
return true;
break;
}
}
return false; /* no conflict between these locks */
}
/**
* Overrides Object.equals()
*/
public boolean equals (Object otherLock)
{
if (otherLock instanceof Lock)
return equals((Lock) otherLock);
else
return false;
}
/**
* Are the two locks equal?
*
* @return true if the locks are equal, false
* otherwise.
*/
public boolean equals (Lock otherLock)
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::equals("
+ otherLock + ")\n" + "\tLock 1:\n" + this + "\n"
+ "\tLock 2:\n" + otherLock);
}
if (this == otherLock)
return true;
if ((lMode == otherLock.lMode) && (owners.equals(otherLock.owners))
&& (currentStatus == otherLock.currentStatus))
{
return true;
}
return false;
}
/**
* Overrides Object.toString()
*/
public String toString ()
{
StringWriter strm = new StringWriter();
strm.write("Lock object : \n");
strm.write("\tunique id is : " + get_uid() + "\n");
strm.write("\tcurrent_status : "
+ LockStatus.printString(currentStatus));
strm.write("\n\tMode : " + LockMode.stringForm(lMode));
strm.write("\n\tOwner List : \n");
owners.print(new PrintWriter(strm));
return strm.toString();
}
/**
* functions inherited from StateManager
*/
public void print (PrintWriter strm)
{
strm.print(toString());
}
/**
* Carefully restore the state of a Lock.
*
* @return true if successful, false otherwise.
*/
public boolean restore_state (InputObjectState os, int ot)
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::restore_state(" + os + ", " + ot + ")");
}
ActionHierarchy ah = new ActionHierarchy(0);
try
{
currentStatus = os.unpackInt();
lMode = os.unpackInt();
ah.unpack(os);
owners = ah;
return true;
}
catch (IOException e)
{
return false;
}
}
/**
* Save the state of a lock object.
*
* @return true if successful, false otherwise.
*/
public boolean save_state (OutputObjectState os, int ot)
{
if (txojLogger.logger.isTraceEnabled()) {
txojLogger.logger.trace("Lock::save_state("
+ os + ", " + ot + ")");
}
try
{
os.packInt(currentStatus);
os.packInt(lMode);
owners.pack(os);
return os.valid();
}
catch (IOException e)
{
return false;
}
}
/**
* Overrides StateManager.type()
*/
public String type ()
{
return "/StateManager/Lock";
}
/**
* Get the next lock in the chain.
*/
protected Lock getLink ()
{
return nextLock;
}
/**
* Set the next lock in the chain.
*/
protected void setLink (Lock pointTo)
{
nextLock = pointTo;
}
private int currentStatus;/* Current status of lock */
private Lock nextLock;
private int lMode; /* Typically READ or WRITE */
private ActionHierarchy owners; /* Uid of owner action (faked if none) */
private static Uid applicUid = null; /* In case lock set outside AA */
private static int applicPid = com.arjuna.ats.arjuna.utils.Utility.getpid(); /*
* process
* id
*/
}