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Core module containing all storage functionality.
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/**
 * Copyright (c) 2011, University of Konstanz, Distributed Systems Group
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * * 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.
 * * Neither the name of the University of Konstanz nor the
 * names of its contributors may be used to endorse or promote products
 * derived from this software 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  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.treetank.access;

import static com.google.common.base.Objects.toStringHelper;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;

import java.io.File;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;

import org.treetank.access.conf.ResourceConfiguration;
import org.treetank.access.conf.SessionConfiguration;
import org.treetank.access.conf.StorageConfiguration;
import org.treetank.api.IBucketReadTrx;
import org.treetank.api.IBucketWriteTrx;
import org.treetank.api.ISession;
import org.treetank.bucket.IConstants;
import org.treetank.bucket.MetaBucket;
import org.treetank.bucket.RevisionRootBucket;
import org.treetank.bucket.UberBucket;
import org.treetank.bucket.interfaces.IReferenceBucket;
import org.treetank.exception.TTException;
import org.treetank.exception.TTIOException;
import org.treetank.io.IBackendReader;
import org.treetank.io.IBackendWriter;
import org.treetank.io.IOUtils;

/**
 * Session
 * 
 * 
 * Makes sure that there only is a single session instance bound to a TreeTank file.
 * 
 */
public final class Session implements ISession {

    /** Session configuration. */
    private final ResourceConfiguration mResourceConfig;

    /** Session configuration. */
    protected final SessionConfiguration mSessionConfig;

    /** Storage for centralized closure of related Sessions. */
    private final Storage mDatabase;

    /** Strong reference to uber bucket before the begin of a write transaction. */
    private AtomicReference mLastCommittedUberBucket;

    /** Remember the write separately because of the concurrent writes. */
    private final Set mBucketTrxs;

    /** Determines if session was closed. */
    private transient boolean mClosed;

    /** Check if already a Wtx is used. */
    private AtomicBoolean mWriteTransactionUsed;

    /** Future of currently running commit under this Session. */
    private Future mCommitRunning = null;

    /**
     * 
     * Hidden constructor, only visible for the Storage-Class for instantiation.
     * 
     * @param pStorage
     *            Storage for centralized operations on related sessions.
     * @param pSessionConf
     *            StorageConfiguration for general setting about the storage
     * @param pResourceConf
     *            ResourceConfiguration for handling this specific session
     * @param pBucket
     *            to be set.
     * @throws TTException
     */
    protected Session(final Storage pStorage, final ResourceConfiguration pResourceConf,
        final SessionConfiguration pSessionConf, final UberBucket pBucket) throws TTException {
        mDatabase = pStorage;
        mResourceConfig = pResourceConf;
        mSessionConfig = pSessionConf;
        mBucketTrxs = new CopyOnWriteArraySet();
        mClosed = false;
        mLastCommittedUberBucket = new AtomicReference(pBucket);
        mWriteTransactionUsed = new AtomicBoolean(false);
    }

    public IBucketReadTrx beginBucketRtx(final long pRevKey) throws TTException {
        waitForRunningCommit();
        assertAccess(pRevKey);
        final IBackendReader bucketReader = mResourceConfig.mBackend.getReader();
        final RevisionRootBucket revBucket =
            (RevisionRootBucket)bucketReader
                .read(BucketReadTrx.dereferenceLeafOfTree(bucketReader, mLastCommittedUberBucket.get()
                    .getReferenceKeys()[IReferenceBucket.GUARANTEED_INDIRECT_OFFSET], pRevKey)[IConstants.INDIRECT_BUCKET_COUNT.length]);
        final MetaBucket metaBucket =
            (MetaBucket)bucketReader
                .read(revBucket.getReferenceKeys()[RevisionRootBucket.META_REFERENCE_OFFSET]);
        final BucketReadTrx trx =
            new BucketReadTrx(this, mLastCommittedUberBucket.get(), revBucket, metaBucket, bucketReader);
        mBucketTrxs.add(trx);
        return trx;
    }

    public IBucketWriteTrx beginBucketWtx() throws TTException {
        return beginBucketWtx(mLastCommittedUberBucket.get().getRevisionNumber());
    }

    public IBucketWriteTrx beginBucketWtx(final long mRepresentRevision) throws TTException {
        checkState(mWriteTransactionUsed.compareAndSet(false, true),
            "Only one WriteTransaction per Session is allowed");
        waitForRunningCommit();
        assertAccess(mRepresentRevision);
        final IBackendWriter backendWriter = mResourceConfig.mBackend.getWriter();
        final IBucketWriteTrx trx =
            new BucketWriteTrx(this, mLastCommittedUberBucket.get(), backendWriter, mRepresentRevision);
        mBucketTrxs.add(trx);
        return trx;
    }

    /**
     * {@inheritDoc}
     */
    public synchronized boolean close() throws TTException {
        waitForRunningCommit();
        if (!mClosed) {
            // Forcibly close all open transactions.
            for (final IBucketReadTrx rtx : mBucketTrxs) {
                // If the transaction is a WriteTrx, clear log aswell..
                if (rtx instanceof BucketWriteTrx) {
                    ((BucketWriteTrx)rtx).clearLog();
                }
                rtx.close();
            }

            // Immediately release all resources.
            mLastCommittedUberBucket = null;
            mBucketTrxs.clear();
            mResourceConfig.mBackend.close();
            mDatabase.mSessions.remove(mSessionConfig.getResource());
            mClosed = true;
            return true;
        } else {
            return false;
        }
    }

    /**
     * {@inheritDoc}
     */
    public boolean truncate() throws TTException {
        checkState(!mClosed, "Session must be opened to truncate.");
        waitForRunningCommit();
        if (mResourceConfig.mBackend.truncate()) {
            // Forcibly close all open transactions.
            for (final IBucketReadTrx rtx : mBucketTrxs) {
                rtx.close();
            }
            // Immediately release all resources.
            mLastCommittedUberBucket = null;
            mBucketTrxs.clear();
            mDatabase.mSessions.remove(mSessionConfig.getResource());
            mClosed = true;
            return IOUtils.recursiveDelete(new File(new File(mDatabase.getLocation(),
                StorageConfiguration.Paths.Data.getFile().getName()), mSessionConfig.getResource()));
        } else {
            return false;
        }
    }

    /**
     * Asserting access on this session with the denoted revision number
     * 
     * @param pRevision
     *            the revision to be validated
     * @throws TTIOException
     */
    private void assertAccess(final long pRevision) throws TTIOException {
        checkState(!mClosed, "Session is already closed.");
        checkArgument(pRevision <= getMostRecentVersion(), "Revision must not be bigger than %s",
            getMostRecentVersion());
    }

    protected void setLastCommittedUberBucket(final UberBucket pBucket) {
        this.mLastCommittedUberBucket.set(pBucket);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public long getMostRecentVersion() throws TTIOException {
        waitForRunningCommit();
        return mLastCommittedUberBucket.get().getRevisionNumber();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public ResourceConfiguration getConfig() {
        return mResourceConfig;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean deregisterBucketTrx(IBucketReadTrx pTrx) throws TTIOException {
        if (pTrx instanceof IBucketWriteTrx) {
            mWriteTransactionUsed.set(false);
        }
        return mBucketTrxs.remove(pTrx);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String toString() {
        return toStringHelper(this).add("mResourceConfig", mResourceConfig).add("mSessionConfig",
            mSessionConfig).add("mLastCommittedUberBucket", mLastCommittedUberBucket).add(
            "mLastCommittedUberBucket", mBucketTrxs).toString();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void waitForRunningCommit() throws TTIOException {
        if (mCommitRunning != null) {
            try {
                // long time = System.currentTimeMillis();
                mCommitRunning.get();
                // System.out.println(System.currentTimeMillis() - time);
                mCommitRunning = null;
            } catch (InterruptedException | ExecutionException exc) {
                throw new TTIOException(exc);
            }
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void setRunningCommit(Future pRunningCommit) {
        mCommitRunning = pRunningCommit;

    }
}