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/*
* 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.commons.lang3.concurrent;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.function.Function;
import org.apache.commons.lang3.exception.ExceptionUtils;
/**
* Definition of an interface for a wrapper around a calculation that takes a single parameter and returns a result. The
* results for the calculation will be cached for future requests.
*
*
* This is not a fully functional cache, there is no way of limiting or removing results once they have been generated.
* However, it is possible to get the implementation to regenerate the result for a given parameter, if an error was
* thrown during the previous calculation, by setting the option during the construction of the class. If this is not
* set the class will return the cached exception.
*
*
* Thanks should go to Brian Goetz, Tim Peierls and the members of JCP JSR-166 Expert Group for coming up with the
* original implementation of the class. It was also published within Java Concurrency in Practice as a sample.
*
*
* @param the type of the input to the calculation
* @param the type of the output of the calculation
*
* @since 3.6
*/
public class Memoizer implements Computable {
private final ConcurrentMap> cache = new ConcurrentHashMap<>();
private final Function> mappingFunction;
private final boolean recalculate;
/**
* Constructs a Memoizer for the provided Computable calculation.
*
*
* If a calculation throws an exception for any reason, this exception will be cached and returned for all future
* calls with the provided parameter.
*
*
* @param computable the computation whose results should be memorized
*/
public Memoizer(final Computable computable) {
this(computable, false);
}
/**
* Constructs a Memoizer for the provided Computable calculation, with the option of whether a Computation that
* experiences an error should recalculate on subsequent calls or return the same cached exception.
*
* @param computable the computation whose results should be memorized
* @param recalculate determines whether the computation should be recalculated on subsequent calls if the previous call
* failed
*/
public Memoizer(final Computable computable, final boolean recalculate) {
this.recalculate = recalculate;
this.mappingFunction = k -> FutureTasks.run(() -> computable.compute(k));
}
/**
* Constructs a Memoizer for the provided Function calculation.
*
*
* If a calculation throws an exception for any reason, this exception will be cached and returned for all future
* calls with the provided parameter.
*
*
* @param function the function whose results should be memorized
* @since 2.13.0
*/
public Memoizer(final Function function) {
this(function, false);
}
/**
* Constructs a Memoizer for the provided Function calculation, with the option of whether a Function that
* experiences an error should recalculate on subsequent calls or return the same cached exception.
*
* @param function the computation whose results should be memorized
* @param recalculate determines whether the computation should be recalculated on subsequent calls if the previous call
* failed
* @since 2.13.0
*/
public Memoizer(final Function function, final boolean recalculate) {
this.recalculate = recalculate;
this.mappingFunction = k -> FutureTasks.run(() -> function.apply(k));
}
/**
* This method will return the result of the calculation and cache it, if it has not previously been calculated.
*
*
* This cache will also cache exceptions that occur during the computation if the {@code recalculate} parameter in the
* constructor was set to {@code false}, or not set. Otherwise, if an exception happened on the previous calculation,
* the method will attempt again to generate a value.
*
*
* @param arg the argument for the calculation
* @return the result of the calculation
* @throws InterruptedException thrown if the calculation is interrupted
*/
@Override
public O compute(final I arg) throws InterruptedException {
while (true) {
final Future future = cache.computeIfAbsent(arg, mappingFunction);
try {
return future.get();
} catch (final CancellationException e) {
cache.remove(arg, future);
} catch (final ExecutionException e) {
if (recalculate) {
cache.remove(arg, future);
}
throw launderException(e.getCause());
}
}
}
/**
* This method launders a Throwable to either a RuntimeException, Error or any other Exception wrapped in an
* IllegalStateException.
*
* @param throwable the throwable to laundered
* @return a RuntimeException, Error or an IllegalStateException
*/
private RuntimeException launderException(final Throwable throwable) {
throw new IllegalStateException("Unchecked exception", ExceptionUtils.throwUnchecked(throwable));
}
}