gradle-master/subprojects/persistent-cache/src/main/java/org/gradle/cache/internal/DefaultMultiProcessSafeIndexedCache.java
/*
 * Copyright 2011 the original author or authors.
 *
 * 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 org.gradle.cache.internal;

import org.gradle.cache.FileAccess;
import org.gradle.cache.FileIntegrityViolationException;
import org.gradle.cache.FileLock;
import org.gradle.cache.MultiProcessSafeIndexedCache;
import org.gradle.cache.internal.btree.BTreePersistentIndexedCache;
import org.gradle.internal.Factory;

import java.util.function.Function;

public class DefaultMultiProcessSafeIndexedCache<K, V> implements MultiProcessSafeIndexedCache<K, V> {
    private final FileAccess fileAccess;
    private final Factory<BTreePersistentIndexedCache<K, V>> factory;
    private BTreePersistentIndexedCache<K, V> cache;

    public DefaultMultiProcessSafeIndexedCache(Factory<BTreePersistentIndexedCache<K, V>> factory, FileAccess fileAccess) {
        this.factory = factory;
        this.fileAccess = fileAccess;
    }

    @Override
    public String toString() {
        return fileAccess.toString();
    }

    @Override
    public V getIfPresent(final K key) {
        final BTreePersistentIndexedCache<K, V> cache = getCache();
        try {
            return fileAccess.readFile((Factory<V>) () -> cache.get(key));
        } catch (FileIntegrityViolationException e) {
            return null;
        }
    }

    @Override
    public V get(K key, Function<? super K, ? extends V> producer) {
        V value = getIfPresent(key);
        if (value == null) {
            value = producer.apply(key);
            put(key, value);
        }
        return value;
    }

    @Override
    public void put(final K key, final V value) {
        final BTreePersistentIndexedCache<K, V> cache = getCache();
        // Use writeFile because the cache can internally recover from datafile
        // corruption, so we don't care at this level if it's corrupt
        fileAccess.writeFile(() -> cache.put(key, value));
    }

    @Override
    public void remove(final K key) {
        final BTreePersistentIndexedCache<K, V> cache = getCache();
        // Use writeFile because the cache can internally recover from datafile
        // corruption, so we don't care at this level if it's corrupt
        fileAccess.writeFile(() -> cache.remove(key));
    }

    @Override
    public void afterLockAcquire(FileLock.State currentCacheState) {
    }

    @Override
    public void finishWork() {
        if (cache != null) {
            try {
                fileAccess.writeFile(() -> cache.close());
            } finally {
                cache = null;
            }
        }
    }

    @Override
    public void beforeLockRelease(FileLock.State currentCacheState) {
    }

    private BTreePersistentIndexedCache<K, V> getCache() {
        if (cache == null) {
            // Use writeFile because the cache can internally recover from datafile
            // corruption, so we don't care at this level if it's corrupt
            fileAccess.writeFile(() -> cache = factory.create());
        }
        return cache;
    }
}
