[tryout fix] concurrency bug in NamespacedHierarchicalStore#computeIfAbsent(Object, Object, Function) junit-team#5171 junit-team#5209

Signed-off-by: Vincent Potucek <vpotucek@me.com>

Author: Vincent Potucek

junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStore.java

@@ -30,6 +30,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.NonNull;
 import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
@@ -244,16 +245,10 @@ public <K, V> Object computeIfAbsent(N namespace, K key, Function<? super K, ? e
 		StoredValue storedValue = getStoredValue(compositeKey);
 		var result = StoredValue.evaluateIfNotNull(storedValue);
 		if (result == null) {
-			var value = storedValues.compute(compositeKey, (__, currentValue) -> {
-				if (currentValue == null || currentValue.equals(storedValue)) {
-					rejectIfClosed();
-					return newStoredValue(new MemoizingSupplier(() -> {
-						rejectIfClosed();
-						return requireNonNull(defaultCreator.apply(key));
-					}));
-				}
-				return currentValue;
-			});
+			var value = storedValues.compute(compositeKey, (__, currentValue) ->
+					currentValue != null && !currentValue.equals(storedValue)
+					? currentValue
+					: getStoredValue(key, defaultCreator));
 			try {
 				return requireNonNull(value.evaluate());
 			}
@@ -267,6 +262,14 @@ public <K, V> Object computeIfAbsent(N namespace, K key, Function<? super K, ? e
 		return result;
 	}
 
+	private <K, V> StoredValue getStoredValue(K key, Function<? super K, ? extends V> defaultCreator) {
+		rejectIfClosed();
+		return newStoredValue(new MemoizingSupplier(() -> {
+			rejectIfClosed();
+			return requireNonNull(defaultCreator.apply(key));
+		}));
+	}
+
 	/**
 	 * Get the value stored for the supplied namespace and key in this store or
 	 * the parent store, if present, or call the supplied function to compute it