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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
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/*
 * 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.cassandra.hints;

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.Stream;

import com.google.common.collect.ImmutableMap;

import org.apache.cassandra.io.FSReadError;
import org.apache.cassandra.utils.NativeLibrary;
import org.apache.cassandra.utils.SyncUtil;

import static java.util.stream.Collectors.groupingBy;

/**
 * A simple catalog for easy host id -> {@link HintsStore} lookup and manipulation.
 */
final class HintsCatalog
{
    private final File hintsDirectory;
    private final Map stores;
    private final ImmutableMap writerParams;

    private HintsCatalog(File hintsDirectory, ImmutableMap writerParams, Map> descriptors)
    {
        this.hintsDirectory = hintsDirectory;
        this.writerParams = writerParams;
        this.stores = new ConcurrentHashMap<>();

        for (Map.Entry> entry : descriptors.entrySet())
            stores.put(entry.getKey(), HintsStore.create(entry.getKey(), hintsDirectory, writerParams, entry.getValue()));
    }

    /**
     * Loads hints stores from a given directory.
     */
    static HintsCatalog load(File hintsDirectory, ImmutableMap writerParams)
    {
        try
        {
            Map> stores =
                Files.list(hintsDirectory.toPath())
                     .filter(HintsDescriptor::isHintFileName)
                     .map(HintsDescriptor::readFromFile)
                     .collect(groupingBy(h -> h.hostId));
            return new HintsCatalog(hintsDirectory, writerParams, stores);
        }
        catch (IOException e)
        {
            throw new FSReadError(e, hintsDirectory);
        }
    }

    Stream stores()
    {
        return stores.values().stream();
    }

    void maybeLoadStores(Iterable hostIds)
    {
        for (UUID hostId : hostIds)
            get(hostId);
    }

    HintsStore get(UUID hostId)
    {
        // we intentionally don't just return stores.computeIfAbsent() because it's expensive compared to simple get(),
        // and in this case would also allocate for the capturing lambda; the method is on a really hot path
        HintsStore store = stores.get(hostId);
        return store == null
             ? stores.computeIfAbsent(hostId, (id) -> HintsStore.create(id, hintsDirectory, writerParams, Collections.emptyList()))
             : store;
    }

    /**
     * Delete all hints for all host ids.
     *
     * Will not delete the files that are currently being dispatched, or written to.
     */
    void deleteAllHints()
    {
        stores.keySet().forEach(this::deleteAllHints);
    }

    /**
     * Delete all hints for the specified host id.
     *
     * Will not delete the files that are currently being dispatched, or written to.
     */
    void deleteAllHints(UUID hostId)
    {
        HintsStore store = stores.get(hostId);
        if (store != null)
            store.deleteAllHints();
    }

    /**
     * @return true if at least one of the stores has a file pending dispatch
     */
    boolean hasFiles()
    {
        return stores().anyMatch(HintsStore::hasFiles);
    }

    void exciseStore(UUID hostId)
    {
        deleteAllHints(hostId);
        stores.remove(hostId);
    }

    void fsyncDirectory()
    {
        int fd = NativeLibrary.tryOpenDirectory(hintsDirectory.getAbsolutePath());
        if (fd != -1)
        {
            SyncUtil.trySync(fd);
            NativeLibrary.tryCloseFD(fd);
        }
    }

    ImmutableMap getWriterParams()
    {
        return writerParams;
    }
}