modules/core/src/main/java/org/apache/ignite/internal/processors/cache/persistence/wal/aware/SegmentLockStorage.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.ignite.internal.processors.cache.persistence.wal.aware;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.ignite.internal.processors.cache.persistence.wal.FileWriteAheadLogManager;

/**
 * Lock on segment protects from archiving segment.
 */
public class SegmentLockStorage extends SegmentObservable {
    /**
     * Maps absolute segment index to locks counter. Lock on segment protects from archiving segment and may come from
     * {@link FileWriteAheadLogManager.RecordsIterator} during WAL replay. Map itself is guarded by <code>this</code>.
     */
    private Map<Long, Integer> locked = new ConcurrentHashMap<>();

    /**
     * Check if WAL segment locked (protected from move to archive)
     *
     * @param absIdx Index for check reservation.
     * @return {@code True} if index is locked.
     */
    public boolean locked(long absIdx) {
        return locked.containsKey(absIdx);
    }

    /**
     * @param absIdx Segment absolute index.
     * @return <ul><li>{@code True} if can read, no lock is held, </li><li>{@code false} if work segment, need release
     * segment later, use {@link #releaseWorkSegment} for unlock</li> </ul>
     */
    @SuppressWarnings("NonPrivateFieldAccessedInSynchronizedContext")
    boolean lockWorkSegment(long absIdx) {
        locked.compute(absIdx, (idx, count) -> count == null ? 1 : count + 1);

        return false;
    }

    /**
     * @param absIdx Segment absolute index.
     */
    @SuppressWarnings("NonPrivateFieldAccessedInSynchronizedContext")
    void releaseWorkSegment(long absIdx) {
        locked.compute(absIdx, (idx, count) -> {
            assert count != null && count >= 1 : "cur=" + count + ", absIdx=" + absIdx;

            return count == 1 ? null : count - 1;
        });

        notifyObservers(absIdx);
    }
}