Switched implementation of MpEnvironmentVariablesSource to use an LRU cache

config/config-mp/src/main/java/io/helidon/config/mp/MpEnvironmentVariablesSource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2021 Oracle and/or its affiliates.
+ * Copyright (c) 2020, 2024 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -36,6 +36,15 @@ class MpEnvironmentVariablesSource implements ConfigSource {
         this.env = Map.copyOf(System.getenv());
     }
 
+    /**
+     * Access internal cache, used for testing.
+     *
+     * @return internal cache
+     */
+    Map<String, Cached> cache() {
+        return cache;
+    }
+
     @Override
     public Set<String> getPropertyNames() {
         return env.keySet();
@@ -50,7 +59,7 @@ public Map<String, String> getProperties() {
     public String getValue(String propertyName) {
         // environment variable config source is immutable - we can safely cache all requested keys, so we
         // do not execute the regular expression on every get
-        return cache.computeIfAbsent(propertyName, theKey -> {
+        Cached cached = cache.computeIfAbsent(propertyName, theKey -> {
             // According to the spec, we have three ways of looking for a property
             // 1. Exact match
             String result = env.get(propertyName);
@@ -66,8 +75,12 @@ public String getValue(String propertyName) {
             // 3. replace same as above, but uppercase
             String rule3 = rule2.toUpperCase();
             result = env.get(rule3);
-            return new Cached(result);
-        }).value;
+            if (result != null) {
+                return new Cached(result);
+            }
+            return null;    // does not cache misses
+        });
+        return cached == null ? null : cached.value;
     }
 
     @Override

config/config-mp/src/test/java/io/helidon/config/mp/MpEnvironmentVariablesSourceTest.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2024 Oracle and/or its affiliates.
+ *
+ * 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 io.helidon.config.mp;
+
+import java.util.UUID;
+import java.util.stream.IntStream;
+
+import org.junit.jupiter.api.Test;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.not;
+import static org.hamcrest.Matchers.is;
+
+class MpEnvironmentVariablesSourceTest {
+
+    @Test
+    void testCacheMissGrowth() {
+        MpEnvironmentVariablesSource source = new MpEnvironmentVariablesSource();
+        assertThat(source.cache().size(), is(0));
+        IntStream.range(0, 10).forEach(i -> {
+            String random = UUID.randomUUID().toString().toLowerCase();
+            assertThat(source.cache().keySet(), not(contains(random)));
+            source.getValue(random);        // lookup miss, should not cache
+            assertThat(source.cache().keySet(), not(contains(random)));
+        });
+        assertThat(source.cache().size(), is(0));
+    }
+}