LANG-740: Implementation of a Memomizer (closes #203)
changes suggested in https://github.com/apache/commons-lang/pull/80: - tabs to spaces - use @Override - remove unused variables - other minimal clean-ups
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pascalschumacher
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9f89fd4626
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@ -55,6 +55,7 @@ The <action> type attribute can be add,update,fix,remove.
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<action issue="LANG-1070" type="fix" dev="pschumacher" due-to="Paul Pogonyshev">ArrayUtils#add confusing example in javadoc</action>
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<action issue="LANG-1271" type="fix" dev="pschumacher" due-to="Pierre Templier">StringUtils#isAnyEmpty and #isAnyBlank should return false for an empty array</action>
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<action issue="LANG-1155" type="fix" dev="pschumacher" due-to="Saif Asif, Thiago Andrade">Add StringUtils#unwrap</action>
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<action issue="LANG-740" type="add" dev="pschumacher" due-to="James Sawle">Implementation of a Memomizer</action>
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<action issue="LANG-1258" type="add" dev="pschumacher" due-to="IG, Grzegorz Rożniecki">Add ArrayUtils#toStringArray method</action>
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<action issue="LANG-1160" type="add" dev="kinow">StringUtils#abbreviate should support 'custom ellipses' parameter</action>
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<action issue="LANG-1270" type="add" dev="pschumacher" due-to="Pierre Templier">Add StringUtils#isAnyNotEmpty and #isAnyNotBlank</action>
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@ -21,17 +21,21 @@
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* <p/>
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* <p>This interface allows for wrapping a calculation into a class so that it maybe passed around an application.</p>
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*
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* @param <A> the type of the input to the calculation
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* @param <V> the type of the output of the calculation
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* @param <I> the type of the input to the calculation
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* @param <O> the type of the output of the calculation
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*
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* @since 3.6
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*/
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public interface Computable<A, V> {
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public interface Computable<I, O> {
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/**
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* This method carries out the given operation with the provided argument.
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*
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* @param arg the argument for the calculation
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* @param arg
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* the argument for the calculation
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* @return the result of the calculation
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* @throws InterruptedException thrown if the calculation is interrupted
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* @throws InterruptedException
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* thrown if the calculation is interrupted
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*/
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V compute(final A arg) throws InterruptedException;
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O compute(final I arg) throws InterruptedException;
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}
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@ -25,88 +25,117 @@
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import java.util.concurrent.FutureTask;
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/**
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* <p>Definition of an interface for a wrapper around a calculation that takes a single parameter and returns a result.
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* The results for the calculation will be cached for future requests.</p>
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* <p/>
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* <p>This is not a fully functional cache, there is no way of limiting or removing results once they have been generated.
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* However, it is possible to get the implementation to regenerate the result for a given parameter, if an error was
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* thrown during the previous calculation, by setting the option during the construction of the class. If this is not
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* set the class will return the cached exception.</p>
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* <p/>
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* <p>Thanks should go to Brian Goetz, Tim Peierls and the members of JCP JSR-166 Expert Group for coming up with the
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* original implementation of the class. It was also published within Java Concurreny in Practice as a sample.</p>
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* <p>
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* Definition of an interface for a wrapper around a calculation that takes a
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* single parameter and returns a result. The results for the calculation will
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* be cached for future requests.
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* </p>
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* <p>
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* This is not a fully functional cache, there is no way of limiting or removing
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* results once they have been generated. However, it is possible to get the
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* implementation to regenerate the result for a given parameter, if an error
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* was thrown during the previous calculation, by setting the option during the
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* construction of the class. If this is not set the class will return the
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* cached exception.
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* </p>
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* <p>
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* Thanks should go to Brian Goetz, Tim Peierls and the members of JCP JSR-166
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* Expert Group for coming up with the original implementation of the class. It
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* was also published within Java Concurrency in Practice as a sample.
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* </p>
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*
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* @param <A> the type of the input to the calculation
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* @param <V> the type of the output of the calculation
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* @param <I>
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* the type of the input to the calculation
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* @param <O>
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* the type of the output of the calculation
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*
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* @since 3.6
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*/
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public class Memoizer<A, V> implements Computable<A, V> {
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private final ConcurrentMap<A, Future<V>> cache
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= new ConcurrentHashMap<A, Future<V>>();
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private final Computable<A, V> c;
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public class Memoizer<I, O> implements Computable<I, O> {
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private final ConcurrentMap<I, Future<O>> cache = new ConcurrentHashMap<>();
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private final Computable<I, O> computable;
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private final boolean recalculate;
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/**
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* <p>Constructs a Memoizer for the provided Computable calculation.</p>
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* <p/>
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* <p>If a calculation is thrown an exception for any reason, this exception will be cached and returned for
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* all future calls with the provided parameter.</p>
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* <p>
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* Constructs a Memoizer for the provided Computable calculation.
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* </p>
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* <p>
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* If a calculation is thrown an exception for any reason, this exception
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* will be cached and returned for all future calls with the provided
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* parameter.
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* </p>
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*
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* @param c the computation whose results should be memorized
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* @param computable
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* the computation whose results should be memorized
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*/
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public Memoizer(Computable<A, V> c) {
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this(c, false);
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public Memoizer(final Computable<I, O> computable) {
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this(computable, false);
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}
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/**
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* <p>Constructs a Memoizer for the provided Computable calculation, with the option of whether a Computation
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* that experiences an error should recalculate on subsequent calls or return the same cached exception.</p>
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* <p>
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* Constructs a Memoizer for the provided Computable calculation, with the
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* option of whether a Computation that experiences an error should
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* recalculate on subsequent calls or return the same cached exception.
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* </p>
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*
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* @param c the computation whose results should be memorized
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* @param recalculate determines whether the computation should be recalculated on subsequent calls if the previous
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* call failed
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* @param computable
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* the computation whose results should be memorized
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* @param recalculate
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* determines whether the computation should be recalculated on
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* subsequent calls if the previous call failed
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*/
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public Memoizer(Computable<A, V> c, boolean recalculate) {
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this.c = c;
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public Memoizer(final Computable<I, O> computable, final boolean recalculate) {
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this.computable = computable;
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this.recalculate = recalculate;
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}
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/**
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* <p>This method will return the result of the calculation and cache it, if it has not previously been calculated.</p>
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* <p/>
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* <p>This cache will also cache exceptions that occur during the computation if the {@code recalculate} parameter is
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* the constructor was set to {@code false}, or not set. Otherwise, if an exception happened on the previous
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* calculation, the method will attempt again to generate a value.</p>
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* <p>
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* This method will return the result of the calculation and cache it, if it
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* has not previously been calculated.
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* </p>
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* <p>
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* This cache will also cache exceptions that occur during the computation
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* if the {@code recalculate} parameter is the constructor was set to
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* {@code false}, or not set. Otherwise, if an exception happened on the
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* previous calculation, the method will attempt again to generate a value.
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* </p>
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*
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* @param arg the argument for the calculation
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* @param arg
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* the argument for the calculation
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* @return the result of the calculation
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* @throws InterruptedException thrown if the calculation is interrupted
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* @throws IllegalStateException a wrapper around any checked exception that occurs during the computation of the result
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* @throws InterruptedException
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* thrown if the calculation is interrupted
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*/
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public V compute(final A arg) throws InterruptedException, IllegalStateException {
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@Override
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public O compute(final I arg) throws InterruptedException {
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while (true) {
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Future<V> f = cache.get(arg);
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if (f == null) {
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Callable<V> eval = new Callable<V>() {
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public V call() throws InterruptedException {
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return c.compute(arg);
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Future<O> future = cache.get(arg);
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if (future == null) {
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Callable<O> eval = new Callable<O>() {
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@Override
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public O call() throws InterruptedException {
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return computable.compute(arg);
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}
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};
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FutureTask<V> ft = new FutureTask<V>(eval);
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f = cache.putIfAbsent(arg, ft);
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if (f == null) {
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f = ft;
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ft.run();
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FutureTask<O> futureTask = new FutureTask<>(eval);
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future = cache.putIfAbsent(arg, futureTask);
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if (future == null) {
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future = futureTask;
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futureTask.run();
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}
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}
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try {
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return f.get();
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}
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catch (CancellationException e) {
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cache.remove(arg, f);
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}
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catch (ExecutionException e) {
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return future.get();
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} catch (CancellationException e) {
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cache.remove(arg, future);
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} catch (ExecutionException e) {
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if (recalculate) {
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cache.remove(arg, f);
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cache.remove(arg, future);
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}
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throw launderException(e.getCause());
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@ -115,19 +144,22 @@ public V call() throws InterruptedException {
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}
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/**
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* <p>This method launders a Throwable to either a RuntimeException, Error or any other Exception wrapped
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* in an IllegalStateException.</p>
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* <p>
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* This method launders a Throwable to either a RuntimeException, Error or
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* any other Exception wrapped in an IllegalStateException.
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* </p>
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*
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* @param t the throwable to laundered
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* @param throwable
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* the throwable to laundered
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* @return a RuntimeException, Error or an IllegalStateException
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*/
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private RuntimeException launderException(Throwable t) {
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if (t instanceof RuntimeException) {
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return (RuntimeException) t;
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} else if (t instanceof Error) {
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throw (Error) t;
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private RuntimeException launderException(final Throwable throwable) {
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if (throwable instanceof RuntimeException) {
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return (RuntimeException) throwable;
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} else if (throwable instanceof Error) {
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throw (Error) throwable;
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} else {
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throw new IllegalStateException("Unchecked exception", t);
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throw new IllegalStateException("Unchecked exception", throwable);
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}
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}
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}
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@ -1,3 +1,19 @@
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/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.commons.lang3.concurrent;
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import org.easymock.EasyMockRunner;
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@ -19,7 +35,7 @@ public class MemoizerTest {
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@Test
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public void testOnlyCallComputableOnceIfDoesNotThrowException() throws Exception {
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Integer input = 1;
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Memoizer<Integer, Integer> memoizer = new Memoizer<Integer, Integer>(computable);
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Memoizer<Integer, Integer> memoizer = new Memoizer<>(computable);
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expect(computable.compute(input)).andReturn(input);
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replay(computable);
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@ -30,18 +46,16 @@ public void testOnlyCallComputableOnceIfDoesNotThrowException() throws Exception
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@Test(expected = IllegalStateException.class)
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public void testDefaultBehaviourNotToRecalculateExecutionExceptions() throws Exception {
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Integer input = 1;
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Integer answer = 3;
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Memoizer<Integer, Integer> memoizer = new Memoizer<Integer, Integer>(computable);
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Memoizer<Integer, Integer> memoizer = new Memoizer<>(computable);
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InterruptedException interruptedException = new InterruptedException();
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expect(computable.compute(input)).andThrow(interruptedException);
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replay(computable);
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try {
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memoizer.compute(input);
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fail();
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}
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catch (Throwable ex) {
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//Should always be thrown the first time
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fail("Expected Throwable to be thrown!");
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} catch (Throwable expected) {
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// Should always be thrown the first time
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}
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memoizer.compute(input);
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@ -50,18 +64,16 @@ public void testDefaultBehaviourNotToRecalculateExecutionExceptions() throws Exc
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@Test(expected = IllegalStateException.class)
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public void testDoesNotRecalculateWhenSetToFalse() throws Exception {
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Integer input = 1;
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Integer answer = 3;
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Memoizer<Integer, Integer> memoizer = new Memoizer<Integer, Integer>(computable, false);
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Memoizer<Integer, Integer> memoizer = new Memoizer<>(computable, false);
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InterruptedException interruptedException = new InterruptedException();
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expect(computable.compute(input)).andThrow(interruptedException);
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replay(computable);
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try {
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memoizer.compute(input);
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fail();
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}
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catch (Throwable ex) {
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//Should always be thrown the first time
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fail("Expected Throwable to be thrown!");
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} catch (Throwable expected) {
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// Should always be thrown the first time
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}
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memoizer.compute(input);
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@ -71,27 +83,25 @@ public void testDoesNotRecalculateWhenSetToFalse() throws Exception {
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public void testDoesRecalculateWhenSetToTrue() throws Exception {
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Integer input = 1;
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Integer answer = 3;
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Memoizer<Integer, Integer> memoizer = new Memoizer<Integer, Integer>(computable, true);
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Memoizer<Integer, Integer> memoizer = new Memoizer<>(computable, true);
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InterruptedException interruptedException = new InterruptedException();
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expect(computable.compute(input)).andThrow(interruptedException).andReturn(answer);
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replay(computable);
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try {
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memoizer.compute(input);
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fail();
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}
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catch (Throwable ex) {
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//Should always be thrown the first time
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fail("Expected Throwable to be thrown!");
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} catch (Throwable expected) {
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// Should always be thrown the first time
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}
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assertEquals(answer, memoizer.compute(input));
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}
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@Test(expected = RuntimeException.class)
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public void testWhenComputableThrowsRuntimeException() throws Exception {
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Integer input = 1;
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Memoizer<Integer, Integer> memoizer = new Memoizer<Integer, Integer>(computable);
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Memoizer<Integer, Integer> memoizer = new Memoizer<>(computable);
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RuntimeException runtimeException = new RuntimeException("Some runtime exception");
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expect(computable.compute(input)).andThrow(runtimeException);
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replay(computable);
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@ -102,7 +112,7 @@ public void testWhenComputableThrowsRuntimeException() throws Exception {
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@Test(expected = Error.class)
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public void testWhenComputableThrowsError() throws Exception {
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Integer input = 1;
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Memoizer<Integer, Integer> memoizer = new Memoizer<Integer, Integer>(computable);
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Memoizer<Integer, Integer> memoizer = new Memoizer<>(computable);
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Error error = new Error();
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expect(computable.compute(input)).andThrow(error);
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replay(computable);
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