+ return oldFuture;
+ }
+
+ /*
+ * Note: must NOT invoke params.start() within retrievers.compute(), as start()
+ * may invoke obtain() which would cause a recursive update to the retrievers map.
+ */
+ CompletableFuture<OperationOutcome> future = params.start();
+
+ if ((oldFuture = retrievers.putIfAbsent(name, future)) != null) {