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dhis-2/dhis-api/src/main/java/org/hisp/dhis/cache/SoftCache.java
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| /* | ||
| * Copyright (c) 2004-2024, University of Oslo | ||
| * All rights reserved. | ||
| * | ||
| * Redistribution and use in source and binary forms, with or without | ||
| * modification, are permitted provided that the following conditions are met: | ||
| * Redistributions of source code must retain the above copyright notice, this | ||
| * list of conditions and the following disclaimer. | ||
| * | ||
| * Redistributions in binary form must reproduce the above copyright notice, | ||
| * this list of conditions and the following disclaimer in the documentation | ||
| * and/or other materials provided with the distribution. | ||
| * Neither the name of the HISP project nor the names of its contributors may | ||
| * be used to endorse or promote products derived from this software without | ||
| * specific prior written permission. | ||
| * | ||
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND | ||
| * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED | ||
| * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE | ||
| * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR | ||
| * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES | ||
| * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; | ||
| * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON | ||
| * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | ||
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS | ||
| * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | ||
| */ | ||
| package org.hisp.dhis.cache; | ||
|
|
||
| import java.lang.ref.SoftReference; | ||
| import java.util.concurrent.ConcurrentHashMap; | ||
| import java.util.concurrent.ConcurrentMap; | ||
| import java.util.function.Supplier; | ||
| import javax.annotation.CheckForNull; | ||
| import javax.annotation.Nonnull; | ||
|
|
||
| /** | ||
| * A soft cache uses a concurrent map with {@link java.lang.ref.SoftReference} boxed values. | ||
| * | ||
| * <p>This means the values might get GC-ed if the JVM needs memory. Therefore, when accessing a | ||
| * value by key, a {@link java.util.function.Supplier} needs to be passed in case the value needs | ||
| * re-computing. | ||
| * | ||
| * @author Jan Bernitt | ||
| * @since 2.42 | ||
| */ | ||
| public final class SoftCache<T> { | ||
|
|
||
| private final ConcurrentMap<String, SoftReference<T>> cache = new ConcurrentHashMap<>(); | ||
|
|
||
| /** | ||
| * Access a cached value by key. | ||
| * | ||
| * @param key the key to get from the cache, when null the value is computed and not cached | ||
| * @param onMiss a function to compute the value on a cache miss; the function must not return | ||
| * null | ||
| * @return the cached or computed value | ||
| */ | ||
| @Nonnull | ||
| public T get(@CheckForNull String key, @Nonnull Supplier<T> onMiss) { | ||
| if (key == null) return onMiss.get(); | ||
| Supplier<T> memOnMiss = memorize(onMiss); | ||
| T res = | ||
| cache | ||
| .compute( | ||
| key, | ||
| (k, v) -> { | ||
| if (v == null) return new SoftReference<>(memOnMiss.get()); | ||
| if (v.get() != null) return v; | ||
| return new SoftReference<>(memOnMiss.get()); | ||
| }) | ||
| .get(); | ||
| // in theory the get() of the SoftReference can become null | ||
| // just when it is returned from the map | ||
| // in which case the res is taken directly from the supplier | ||
| // since this should mean the JVM is low on memory | ||
| return res == null ? memOnMiss.get() : res; | ||
| } | ||
|
|
||
| /** | ||
| * @param onMiss assumed expensive to compute | ||
| * @return a supplier that will memorize the result once it has been computed | ||
| */ | ||
| private Supplier<T> memorize(Supplier<T> onMiss) { | ||
| Object[] memorize = new Object[1]; | ||
| return () -> { | ||
| @SuppressWarnings("unchecked") | ||
| T v = (T) memorize[0]; | ||
| if (v != null) return v; | ||
| v = onMiss.get(); | ||
| memorize[0] = v; | ||
| return v; | ||
| }; | ||
| } | ||
| } |
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