NaiveRevisionManager.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.nifi.web.revision;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.apache.nifi.authorization.user.NiFiUser;
import org.apache.nifi.web.InvalidRevisionException;
import org.apache.nifi.web.Revision;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>
 * This class implements a naive approach for Revision Management.
 * Each call into the Revision Manager will block until any previously held
 * lock is expired or unlocked. This provides a very simple solution but can
 * likely be improved by allowing, for instance, multiple threads to obtain
 * temporary locks simultaneously, etc.
 * </p>
 */
public class NaiveRevisionManager implements RevisionManager {
    private static final Logger logger = LoggerFactory.getLogger(NaiveRevisionManager.class);

    private final ConcurrentMap<String, Revision> revisionMap = new ConcurrentHashMap<>();


    @Override
    public void reset(final Collection<Revision> revisions) {
        synchronized (this) { // avoid allowing two threads to reset versions concurrently
            revisionMap.clear();

            for (final Revision revision : revisions) {
                revisionMap.put(revision.getComponentId(), revision);
            }
        }
    }

    @Override
    public List<Revision> getAllRevisions() {
        return new ArrayList<>(revisionMap.values());
    }

    @Override
    public Revision getRevision(final String componentId) {
        return revisionMap.computeIfAbsent(componentId, id -> new Revision(0L, null, componentId));
    }

    @Override
    public <T> T deleteRevision(final RevisionClaim claim, final NiFiUser user, final DeleteRevisionTask<T> task) throws ExpiredRevisionClaimException {
        Objects.requireNonNull(user);
        logger.debug("Attempting to delete revision using {}", claim);
        final List<Revision> revisionList = new ArrayList<>(claim.getRevisions());
        revisionList.sort(new RevisionComparator());

        // Verify the provided revisions.
        String failedId = null;
        for (final Revision revision : revisionList) {
            final Revision curRevision = getRevision(revision.getComponentId());
            if (!curRevision.equals(revision)) {
                throw new ExpiredRevisionClaimException("Invalid Revision was given for component with ID '" + failedId + "'");
            }
        }

        // Perform the action provided
        final T taskResult = task.performTask();

        for (final Revision revision : revisionList) {
            revisionMap.remove(revision.getComponentId());
        }

        return taskResult;
    }

    @Override
    public <T> RevisionUpdate<T> updateRevision(final RevisionClaim originalClaim, final NiFiUser user, final UpdateRevisionTask<T> task) throws ExpiredRevisionClaimException {
        Objects.requireNonNull(user);
        logger.debug("Attempting to update revision using {}", originalClaim);

        final List<Revision> revisionList = new ArrayList<>(originalClaim.getRevisions());
        revisionList.sort(new RevisionComparator());

        String failedId = null;
        for (final Revision revision : revisionList) {
            final Revision currentRevision = getRevision(revision.getComponentId());
            final boolean verified = revision.equals(currentRevision);

            if (!verified) {
                // Throw an Exception indicating that we failed to obtain the locks
                throw new InvalidRevisionException("Invalid Revision was given for component with ID '" + failedId + "'");
            }
        }

        // We successfully verified all revisions.
        logger.debug("Successfully verified Revision Claim for all revisions");

        RevisionUpdate<T> updatedComponent = null;
        try {
            updatedComponent = task.update();
        } finally {
            // Release the lock that we are holding and update the revision.
            // To do this, we need to map the old revision to the new revision
            // so that we have an efficient way to lookup the pairing, so that
            // we can easily obtain the old revision and the new revision for
            // the same component in order to call #unlock on the RevisionLock
            final Map<Revision, Revision> updatedRevisions = new HashMap<>();
            final Map<String, Revision> revisionsByComponentId = new HashMap<>();
            for (final Revision revision : revisionList) {
                updatedRevisions.put(revision, revision);
                revisionsByComponentId.put(revision.getComponentId(), revision);
            }

            if (updatedComponent != null) {
                for (final Revision updatedRevision : updatedComponent.getUpdatedRevisions()) {
                    final Revision oldRevision = revisionsByComponentId.get(updatedRevision.getComponentId());
                    if (oldRevision != null) {
                        updatedRevisions.put(oldRevision, updatedRevision);
                    }
                }
            }

            for (final Revision revision : revisionList) {
                final Revision updatedRevision = updatedRevisions.get(revision);
                revisionMap.put(updatedRevision.getComponentId(), updatedRevision);

                if (updatedRevision.getVersion() != revision.getVersion()) {
                    logger.debug("Unlocked Revision {} and updated associated Version to {}", revision, updatedRevision.getVersion());
                } else {
                    logger.debug("Unlocked Revision {} without updating Version", revision);
                }
            }
        }

        return updatedComponent;
    }
}