currenttransaction.java

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/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 2000,2007 Oracle.  All rights reserved.
 *
 * $Id: CurrentTransaction.java,v 1.46.2.1 2007/02/01 14:49:39 cwl Exp $
 */

package com.sleepycat.collections;

import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;
import java.util.WeakHashMap;

import com.sleepycat.compat.DbCompat;
import com.sleepycat.je.Cursor;
import com.sleepycat.je.CursorConfig;
import com.sleepycat.je.Database;
import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.Environment;
import com.sleepycat.je.EnvironmentConfig;
import com.sleepycat.je.LockMode;
import com.sleepycat.je.Transaction;
import com.sleepycat.je.TransactionConfig;
import com.sleepycat.util.RuntimeExceptionWrapper;

/**
 * Provides access to the current transaction for the current thread within the
 * context of a Berkeley DB environment.  This class provides explicit
 * transaction control beyond that provided by the {@link TransactionRunner}
 * class.  However, both methods of transaction control manage per-thread
 * transactions.
 *
 * @author Mark Hayes
 */
public class CurrentTransaction {

    /* For internal use, this class doubles as an Environment wrapper. */

    private static WeakHashMap envMap = new WeakHashMap();

    private LockMode writeLockMode;
    private boolean cdbMode;
    private boolean txnMode;
    private boolean lockingMode;
    private Environment env;
    private ThreadLocal localTrans = new ThreadLocal();
    private ThreadLocal localCdbCursors;

    /**
     * Gets the CurrentTransaction accessor for a specified Berkeley DB
     * environment.  This method always returns the same reference when called
     * more than once with the same environment parameter.
     *
     * @param env is an open Berkeley DB environment.
     *
     * @return the CurrentTransaction accessor for the given environment, or
     * null if the environment is not transactional.
     */
    public static CurrentTransaction getInstance(Environment env) {

        CurrentTransaction currentTxn = getInstanceInternal(env);
        return currentTxn.isTxnMode() ? currentTxn : null;
    }

    /**
     * Gets the CurrentTransaction accessor for a specified Berkeley DB
     * environment.  Unlike getInstance(), this method never returns null.
     *
     * @param env is an open Berkeley DB environment.
     */
    static CurrentTransaction getInstanceInternal(Environment env) {
        synchronized (envMap) {
            CurrentTransaction myEnv = null;
            WeakReference myEnvRef = (WeakReference) envMap.get(env);
            if (myEnvRef != null) {
                myEnv = (CurrentTransaction) myEnvRef.get();
            }
            if (myEnv == null) {
                myEnv = new CurrentTransaction(env);
                envMap.put(env, new WeakReference(myEnv));
            }
            return myEnv;
        }
    }

    private CurrentTransaction(Environment env) {
        this.env = env;
        try {
            EnvironmentConfig config = env.getConfig();
            txnMode = config.getTransactional();
            lockingMode = DbCompat.getInitializeLocking(config);
            if (txnMode || lockingMode) {
                writeLockMode = LockMode.RMW;
            } else {
                writeLockMode = LockMode.DEFAULT;
            }
            cdbMode = DbCompat.getInitializeCDB(config);
            if (cdbMode) {
                localCdbCursors = new ThreadLocal();
            }
        } catch (DatabaseException e) {
            throw new RuntimeExceptionWrapper(e);
        }
    }

    /**
     * Returns whether environment is configured for locking.
     */
    final boolean isLockingMode() {

        return lockingMode;
    }

    /**
     * Returns whether this is a transactional environment.
     */
    final boolean isTxnMode() {

        return txnMode;
    }

    /**
     * Returns whether this is a Concurrent Data Store environment.
     */
    final boolean isCdbMode() {

        return cdbMode;
    }

    /**
     * Return the LockMode.RMW or null, depending on whether locking is
     * enabled.  LockMode.RMW will cause an error if passed when locking
     * is not enabled.  Locking is enabled if locking or transactions were
     * specified for this environment.
     */
    final LockMode getWriteLockMode() {

        return writeLockMode;
    }

    /**
     * Returns the underlying Berkeley DB environment.
     */
    public final Environment getEnvironment() {

        return env;
    }

    /**
     * Returns the transaction associated with the current thread for this
     * environment, or null if no transaction is active.
     */
    public final Transaction getTransaction() {

        Trans trans = (Trans) localTrans.get();
        return (trans != null) ? trans.txn : null;
    }

    /**
     * Returns whether auto-commit may be performed by the collections API.
     * True is returned if no collections API transaction is currently active,
     * and no XA transaction is currently active.
     */
    boolean isAutoCommitAllowed()
	throws DatabaseException {

        return getTransaction() == null &&
               DbCompat.getThreadTransaction(env) == null;
    }

    /**
     * Begins a new transaction for this environment and associates it with
     * the current thread.  If a transaction is already active for this
     * environment and thread, a nested transaction will be created.
     *
     * @param config the transaction configuration used for calling
     * {@link Environment#beginTransaction}, or null to use the default
     * configuration.
     *
     * @return the new transaction.
     *
     * @throws DatabaseException if the transaction cannot be started, in which
     * case any existing transaction is not affected.
     *
     * @throws IllegalStateException if a transaction is already active and
     * nested transactions are not supported by the environment.
     */
    public final Transaction beginTransaction(TransactionConfig config)
        throws DatabaseException {

        Trans trans = (Trans) localTrans.get();
        if (trans != null) {
            if (trans.txn != null) {
                if (!DbCompat.NESTED_TRANSACTIONS) {
                    throw new IllegalStateException(
                            "Nested transactions are not supported");
                }
                Transaction parentTxn = trans.txn;
                trans = new Trans(trans, config);
                trans.txn = env.beginTransaction(parentTxn, config);
                localTrans.set(trans);
            } else {
                trans.txn = env.beginTransaction(null, config);
                trans.config = config;
            }
        } else {
            trans = new Trans(null, config);
            trans.txn = env.beginTransaction(null, config);
            localTrans.set(trans);
        }
        return trans.txn;
    }

    /**
     * Commits the transaction that is active for the current thread for this
     * environment and makes the parent transaction (if any) the current
     * transaction.
     *
     * @return the parent transaction or null if the committed transaction was
     * not nested.
     *
     * @throws DatabaseException if an error occurs committing the transaction.
     * The transaction will still be closed and the parent transaction will
     * become the current transaction.
     *
     * @throws IllegalStateException if no transaction is active for the
     * current thread for this environment.
     */
    public final Transaction commitTransaction()
        throws DatabaseException, IllegalStateException {