net.openhft.chronicle.queue.impl.single.ReferenceCountedCache Maven / Gradle / Ivy

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Java library for persisted low latency messaging (Java 8+)
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/*
 * Copyright 2016-2022 chronicle.software
 *
 *       https://chronicle.software
 *
 * Licensed 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 net.openhft.chronicle.queue.impl.single;

import net.openhft.chronicle.core.Jvm;
import net.openhft.chronicle.core.io.*;
import net.openhft.chronicle.core.util.ThrowingFunction;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.function.Function;

/**
 * Thread-safe, self-cleaning cache for ReferenceCounted (and Closeable) objects
 */
public class ReferenceCountedCache
        extends AbstractCloseable {

    private final Map cache = new LinkedHashMap<>();
    private final Function transformer;
    private final ThrowingFunction creator;
    private final ReferenceChangeListener referenceChangeListener;

    @SuppressWarnings("this-escape")
    public ReferenceCountedCache(final Function transformer,
                                 final ThrowingFunction creator) {
        this.transformer = transformer;
        this.creator = creator;
        this.referenceChangeListener = new TriggerFlushOnLastReferenceRemoval();

        singleThreadedCheckDisabled(true);
    }

    @NotNull
    V get(@NotNull final K key) throws E {
        throwExceptionIfClosed();

        final V rv;
        synchronized (cache) {
            @Nullable T value = cache.get(key);

            if (value == null) {
                value = creator.apply(key);
                value.reserveTransfer(INIT, this);
                value.addReferenceChangeListener(referenceChangeListener);
                //System.err.println("Reserved " + value.toString() + " by " + this);
                cache.put(key, value);
            }

            // this will add to the ref count and so needs to be done inside of sync block
            rv = transformer.apply(value);
        }

        return rv;
    }

    @Override
    protected void performClose() {
        synchronized (cache) {
            for (T value : cache.values()) {
                releaseResource(value);
            }
            cache.clear();
        }
    }

    private void releaseResource(T value) {
        try {
            if (value != null)
                value.release(this);
        } catch (Exception e) {
            Jvm.debug().on(getClass(), e);
        }
    }

    public void remove(K key) {
        // harmless to call if cache is already closing/closed

        synchronized (cache) {
            releaseResource(cache.remove(key));
        }
    }

    private class TriggerFlushOnLastReferenceRemoval implements ReferenceChangeListener {

        private final Runnable bgCleanup = this::bgCleanup;

        @Override
        public void onReferenceRemoved(ReferenceCounted referenceCounted, ReferenceOwner referenceOwner) {
            if (referenceOwner != ReferenceCountedCache.this && referenceCounted.refCount() == 1) {
                BackgroundResourceReleaser.run(bgCleanup);
            }
        }

        private void bgCleanup() {
            // remove all which have been de-referenced by other than me. Garbagy but rare
            synchronized (cache) {
                cache.entrySet().removeIf(entry -> {
                    T value = entry.getValue();
                    int refCount = value.refCount();
                    if (refCount == 1) {
                        value.release(ReferenceCountedCache.this);
                    }
                    return refCount <= 1;
                });
            }
        }
    }
}