[GitHub] [flink] zentol commented on a change in pull request #11639: [FLINK-16626][runtime] Prevent REST handler from being closed more than once

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zentol commented on a change in pull request #11639: [FLINK-16626][runtime] 
Prevent REST handler from being closed more than once
URL: https://github.com/apache/flink/pull/11639#discussion_r404158544
 
 

 ##########
 File path: 
flink-runtime/src/main/java/org/apache/flink/runtime/rest/handler/AbstractHandler.java
 ##########
 @@ -217,11 +223,17 @@ private void finalizeRequestProcessing(FileUploads 
uploadedFiles) {
                                HttpResponseStatus.INTERNAL_SERVER_ERROR,
                                responseHeaders);
                }
+
        }
 
        @Override
        public final CompletableFuture<Void> closeAsync() {
-               return FutureUtils.composeAfterwards(closeHandlerAsync(), 
inFlightRequestTracker::awaitAsync);
+               if (isHandlerClosed.compareAndSet(false, true)) {
+                       return 
FutureUtils.composeAfterwards(closeHandlerAsync(), 
inFlightRequestTracker::awaitAsync);
+               } else {
+                       log.warn("Handler instance {} had already been closed, 
not allowed to close it again.", this);
 
 Review comment:
   Without a `toString()` implementation the reference to the handler isn't 
that user-friendly; I would instead suggest to use 
`untypedResponseMessageHeaders.getTargetRestEndpointURL`.
   
   Something along the lines of `The handler for the url ({}) was already 
closed, but another attempt at closing it was made.` 

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