[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

@@ -237,26 +237,34 @@ public void close() {
 	 * closed
 	 * @since 6.0
 	 */
+	@SuppressWarnings("ReferenceEquality")
 	@API(status = MAINTAINED, since = "6.0")
 	public <K, V> Object computeIfAbsent(N namespace, K key, Function<? super K, ? extends V> defaultCreator) {
-		Preconditions.notNull(defaultCreator, "defaultCreator must not be null");
-		CompositeKey<N> compositeKey = new CompositeKey<>(namespace, key);
-		StoredValue storedValue = getStoredValue(compositeKey);
+		requireNonNull(defaultCreator);
+		var compositeKey = new CompositeKey<>(namespace, key);
+		var storedValue = getStoredValue(compositeKey);
 		var result = StoredValue.evaluateIfNotNull(storedValue);
 		if (result == null) {
-			StoredValue newStoredValue = this.storedValues.compute(compositeKey, (__, oldStoredValue) -> {
-				if (StoredValue.evaluateIfNotNull(oldStoredValue) == null) {
+			var newStoredValue = this.storedValues.compute(compositeKey, (__, oldStoredValue) -> {
+				if (oldStoredValue == storedValue || oldStoredValue == null) {
 					rejectIfClosed();
-					var computedValue = Preconditions.notNull(defaultCreator.apply(key),
-						"defaultCreator must not return null");
-					return newStoredValue(() -> {
+					return newStoredValue(new MemoizingSupplier(() -> {
 						rejectIfClosed();
-						return computedValue;
-					});
+						return requireNonNull(defaultCreator.apply(key));
+					}));
 				}
 				return oldStoredValue;
 			});
-			return requireNonNull(newStoredValue.evaluate());
+			try {
+				return requireNonNull(newStoredValue.evaluate());
+			}
+			catch (Throwable t) {
+				// If the evaluation fails, remove the failed entry so subsequent calls can retry
+				if (newStoredValue == this.storedValues.get(compositeKey)) {
+					this.storedValues.remove(compositeKey, newStoredValue);
+				}
+				throw t;
+			}
 		}
 		return result;
 	}