Util: Add cache which keeps a soft reference on the values

The values need to implement the SoftCache.Cacheable<K> interface
where K is the key type. By doing this they promise to keep a
reference to the key. Not doing so will eventually cause the value
from being removed from the cache.

utils/build.gradle.kts

@@ -5,4 +5,11 @@ plugins {
 
 dependencies {
     compileOnly(libs.nullabilityAnnotations)
+
+    testImplementation(libs.test.junit.api)
+    testRuntimeOnly(libs.test.junit.engine)
+}
+
+tasks.test {
+    useJUnitPlatform()
 }

utils/src/main/java/com/github/weisj/darklaf/util/cache/SoftCache.java

@@ -0,0 +1,67 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2021 Jannis Weis
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+ * associated documentation files (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge, publish, distribute,
+ * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or
+ * substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
+ * NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+package com.github.weisj.darklaf.util.cache;
+
+import java.lang.ref.Reference;
+import java.lang.ref.SoftReference;
+import java.util.Map;
+import java.util.WeakHashMap;
+
+public class SoftCache<K, V extends SoftCache.Cacheable<K>> {
+
+    private final Map<K, SoftReference<V>> cache = new WeakHashMap<>();
+
+    public V get(final K key) {
+        Reference<V> reference = cache.get(key);
+        if (reference == null) return null;
+        V value = reference.get();
+        if (value == null) {
+            cache.remove(key);
+        }
+        return value;
+    }
+
+    public void put(final K key, final V value) {
+        if (value != null) {
+            cache.put(key, new SoftReference<>(value));
+            value.setCacheKey(key);
+        } else {
+            cache.remove(key);
+        }
+    }
+
+    public void clear() {
+        cache.clear();
+    }
+
+    public int size() {
+        return cache.size();
+    }
+
+    public boolean isEmpty() {
+        return cache.isEmpty();
+    }
+
+    public interface Cacheable<K> {
+        void setCacheKey(final K key);
+    }
+}

utils/src/main/module/module-info.java

@@ -29,6 +29,7 @@ module darklaf.utils {
     requires static annotations;
 
     exports com.github.weisj.darklaf.util;
+    exports com.github.weisj.darklaf.util.cache;
     exports com.github.weisj.darklaf.util.graphics;
     exports com.github.weisj.darklaf.util.value;
 }

utils/src/test/java/com/github/weisj/darklaf/util/cache/SoftCacheTest.java

@@ -0,0 +1,78 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2021 Jannis Weis
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+ * associated documentation files (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge, publish, distribute,
+ * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or
+ * substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
+ * NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+package com.github.weisj.darklaf.util.cache;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.function.Supplier;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class SoftCacheTest {
+
+    @Test
+    void testValuesAreReleased() {
+        final int count = 500;
+        SoftCache<TestKey, TestValue> cache = new SoftCache<>();
+        Set<TestValue> hardReferences = new HashSet<>();
+        for (int i = 0; i < count; i++) {
+            TestValue value = new TestValue();
+            TestKey key = new TestKey();
+            hardReferences.add(value);
+            cache.put(key, value);
+            Assertions.assertEquals(key, value.key);
+        }
+        Assertions.assertEquals(count, hardReferences.size());
+        Assertions.assertEquals(count, cache.size());
+
+        hardReferences.clear();
+
+        waitForGarbageCollection(() -> !cache.isEmpty());
+    }
+
+    @SuppressWarnings({"unused"})
+    private void waitForGarbageCollection(final Supplier<Boolean> checker) {
+        while (checker.get()) {
+            Object object = null;
+            try {
+                object = new int[10][10][10][10][10][10][10][10][10][10][10][10];
+            } catch (OutOfMemoryError ignored) {
+            }
+            System.out.println(object);
+            System.gc();
+        }
+    }
+
+    private static class TestKey {
+    }
+
+    private static class TestValue implements SoftCache.Cacheable<TestKey> {
+        @SuppressWarnings({"FieldCanBeLocal", "unused"})
+        private TestKey key;
+
+        @Override
+        public void setCacheKey(TestKey key) {
+            this.key = key;
+        }
+    }
+}