transactionmanagerimpl.java

开源的axion的数据库代码

/*
 * $Id: TransactionManagerImpl.java,v 1.12 2003/06/10 22:53:06 morgand Exp $
 * =======================================================================
 * Copyright (c) 2002 Axion Development Team.  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.
 *
 * 3. The names "Tigris", "Axion", nor the names of its contributors may
 *    not be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. Products derived from this software may not be called "Axion", nor
 *    may "Tigris" or "Axion" appear in their names without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT
 * OWNER 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.axiondb.engine;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.axiondb.AxionException;
import org.axiondb.Database;
import org.axiondb.Transaction;
import org.axiondb.TransactionConflictException;
import org.axiondb.TransactionManager;

/**
 * An implemenation of {@link TransactionManager} currently
 * only supportd {@link SnapshotIsolationTransaction}s.
 * 
 * @version $Revision: 1.12 $ $Date: 2003/06/10 22:53:06 $
 * @author Rodney Waldhoff
 */
public class TransactionManagerImpl implements TransactionManager {
    public TransactionManagerImpl(Database db) {
        _database = db;
    }
    
    public synchronized Transaction createTransaction() throws AxionException {       
        if(_log.isDebugEnabled()) {
            _log.debug("createTransaction()");
        }
        assertNotShutdown();
        Transaction t = new SnapshotIsolationTransaction(getLastCommittedTransaction());
        _openTransactions.add(t);
        if(_log.isDebugEnabled()) {
            _log.debug("createTransaction(): created transaction " + t);
        }
        return t;
    }
    
    public synchronized void commitTransaction(Transaction t) throws AxionException {
        if(_log.isDebugEnabled()) {
            _log.debug("commitTransaction(): committing transaction " + t);
        }
        assertNotShutdown();
        if(t.getModifiedTables().isEmpty()) {
            t.commit();
            t.apply();
            _openTransactions.remove(t);
        } else {
            // check for conflicts
            Iterator iter = null;
            {
                int index = _committedTransactions.indexOf(t.getOpenOnTransaction());
                if(-1 == index) {
                    iter = _committedTransactions.iterator();
                } else {
                    iter = _committedTransactions.subList(index+1,_committedTransactions.size()).iterator();
                }
            }
            
            while(iter.hasNext()) {
                Transaction c = (Transaction)(iter.next());
                if(inConflict(t,c)) {
                    _log.debug("commitTransaction(): conflict found.");
                    throw new TransactionConflictException("Transaction conflict.");
                }
            }
            
            t.commit();
            _committedTransactions.add(t);
            _openTransactions.remove(t);
        }
        tryToApply();
    }
    
    public synchronized void abortTransaction(Transaction t) throws AxionException {
        if(_log.isDebugEnabled()) {
            _log.debug("abortTransaction(): aborting transaction " + t);
        }
        assertNotShutdown();
        t.rollback();
        _openTransactions.remove(t);
        tryToApply();
    }
    
    public synchronized void shutdown() throws AxionException {
        _log.debug("shutdown()");
        for(int i=_openTransactions.size()-1;i>=0;i--) {
            Transaction t = (Transaction)(_openTransactions.get(i));
            t.rollback();
        }
        _openTransactions.clear();
        tryToApply();
        _database.shutdown();
        _database = null;
    }
    
    public synchronized boolean isShutdown() {
        return null == _database;
    }
    
    private boolean inConflict(Transaction newT, Transaction oldT) {
        // if the new transaction changed anything
        if(!newT.getModifiedTables().isEmpty()) {
            // then check that none of the tables read were changed
            // by the already committed transaction
            // (note that this is much too strong of a conflict detection
            // alogrithm, it'll give a lot of false conflicts).
            if(CollectionUtils.containsAny(newT.getReadTables(),oldT.getModifiedTables())) {
                return true;
            } else {
                return false;
            }
        } else {
            return false;
        }
    }

    private void assertNotShutdown() throws AxionException {
        if(isShutdown()) {
            throw new AxionException("Already shutdown");
        }
    }
    
    private void tryToApply() throws AxionException {
        if(_log.isDebugEnabled()) {
            _log.debug("tryToApply()");
        }
        if((!NEVER_APPLY) && _openTransactions.isEmpty()) {
            Iterator iter = _committedTransactions.iterator();
            while(iter.hasNext()) {
                Transaction t = (Transaction)(iter.next());
                t.apply();
                iter.remove();
            }
        }
    }
    
    private Database getLastCommittedTransaction() {
        if(_committedTransactions.isEmpty()) {
            return _database;
        } else {
            return (Database)(_committedTransactions.get(_committedTransactions.size()-1));
        }
    }
    
    private List _committedTransactions = new ArrayList();
    private List _openTransactions = new ArrayList();
    private Database _database = null;

    // allow a System property to indicate that we should never apply a transaction
    protected static final boolean NEVER_APPLY = Boolean.getBoolean("org.axiondb.engine.TransactionManagerImpl.NEVER_APPLY");
    private static Log _log = LogFactory.getLog(TransactionManagerImpl.class);
    
}