org.conqat.lib.commons.cache4j.BasicCache Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of teamscale-lib-commons Show documentation
Provides common utility functions
The newest version!
/*
 * Copyright (c) CQSE GmbH
 *
 * 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.conqat.lib.commons.cache4j;

import org.conqat.lib.commons.cache4j.backend.ICacheBackend;
import org.conqat.lib.commons.error.NeverThrownRuntimeException;
import org.conqat.lib.commons.factory.IParameterizedFactory;

/**
 * Basic implementation of a cache.
 * 
 * @param 
 *            the key type. This must have both {@link Object#equals(Object)} and
 *            {@link Object#hashCode()} correctly implemented.
 * @param 
 *            the value type. It is generally recommended to use an immutable type here, but this is
 *            not required.
 * @param 
 *            the type of exception thrown. If no exception will be throws, use
 *            {@link NeverThrownRuntimeException}.
 */
public class BasicCache implements ICache {

	/** The name of this cache (e.g. used for statistics). */
	private final String name;

	/** The cache backend. */
	private ICacheBackend backend;

	/** The factory used to create new elements. */
	private final IParameterizedFactory factory;

	/**
	 * Counts the number of cache hits. This variable is not synchronized in any way, so multi-threaded
	 * usage of this class may lead to incorrect results. However, the amount of error is small enough
	 * to be tolerated, while the performance impact of synchronization is not.
	 */
	private int hits = 0;

	/**
	 * Counts the number of cache misses. This variable is not synchronized in any way, so
	 * multi-threaded usage of this class may lead to incorrect results. However, the amount of error is
	 * small enough to be tolerated, while the performance impact of synchronization is not.
	 */
	private int misses = 0;

	/** Accumulated cost of cache misses in milliseconds. */
	private long missCostMillis = 0;

	/** Constructor. */
	public BasicCache(String name, IParameterizedFactory factory, ICacheBackend backend) {
		this.name = name;
		this.factory = factory;
		this.backend = backend;
	}

	/** {@inheritDoc} */
	@Override
	public String getName() {
		return name;
	}

	/** {@inheritDoc} */
	@Override
	public void clear(boolean allThreads) {
		backend = backend.newInstance();
	}

	/** {@inheritDoc} */
	@Override
	public V obtain(K key) throws X {
		V value = backend.retrieve(key);

		if (value != null) {
			hits++;
			return value;
		}

		misses++;

		long start = System.currentTimeMillis();

		value = factory.create(key);
		backend.store(key, value);

		missCostMillis += System.currentTimeMillis() - start;

		return value;
	}

	/** {@inheritDoc} */
	@Override
	public int getHits() {
		return hits;
	}

	/** {@inheritDoc} */
	@Override
	public int getMisses() {
		return misses;
	}

	/** {@inheritDoc} */
	@Override
	public long getMissCostMillis() {
		return missCostMillis;
	}
}