gradle-master/subprojects/scala/src/main/java/org/gradle/api/internal/tasks/scala/GuavaBackedClassLoaderCache.java
/*
 * Copyright 2020 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.api.internal.tasks.scala;


import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.RemovalListener;
import com.google.common.cache.RemovalNotification;

import java.util.concurrent.Callable;

/**
 * Simple guava-based classloader cache. Usually used with a very small size (&lt; 10),
 * as classloaders are strongly referenced.
 *
 * Keeping them strongly referenced allows us to correctly release resources for the evicted entries.
 */
public class GuavaBackedClassLoaderCache<K> implements AutoCloseable {
    private final Cache<K, ClassLoader> cache;


    public GuavaBackedClassLoaderCache(int maxSize) {
        cache = CacheBuilder
            .newBuilder()
            .maximumSize(maxSize)
            .removalListener(new RemovalListener<K, ClassLoader>() {
                @Override
                public void onRemoval(RemovalNotification<K, ClassLoader> notification) {
                    ClassLoader value = notification.getValue();
                    if (value instanceof AutoCloseable) {
                        try {
                            ((AutoCloseable) value).close();
                        } catch(Exception ex) {
                            throw new RuntimeException("Failed to close classloader", ex);
                        }
                    }
                }
            })
            .build();
    }

    public ClassLoader get(K key, Callable<ClassLoader> loader) throws Exception {
        return cache.get(key, loader);
    }

    public void clear() {
        cache.invalidateAll();
    }

    @Override
    public void close() {
        cache.invalidateAll();
    }
}
