[GitHub] [pinot] navina commented on a change in pull request #8272: Fix bug in GrpcBrokerRequestHandler: exceptions are suppressed

[GitBox <gi...@apache.org>]

navina commented on a change in pull request #8272:
URL: https://github.com/apache/pinot/pull/8272#discussion_r817385408



##########
File path: pinot-core/src/main/java/org/apache/pinot/core/query/reduce/StreamingReduceService.java
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@@ -106,15 +108,17 @@ public BrokerResponseNative reduceOnStreamResponse(BrokerRequest brokerRequest,
     return brokerResponseNative;
   }
 
-  private static void processIterativeServerResponse(StreamingReducer reducer, ExecutorService executorService,
+  @VisibleForTesting
+  static void processIterativeServerResponse(StreamingReducer reducer, ExecutorService executorService,
       Map<ServerRoutingInstance, Iterator<Server.ServerResponse>> serverResponseMap, long reduceTimeOutMs,
-      ExecutionStatsAggregator aggregator) throws Exception {
+      ExecutionStatsAggregator aggregator) throws ExecutionException {
     int cnt = 0;
-    Future[] futures = new Future[serverResponseMap.size()];
-    CountDownLatch countDownLatch = new CountDownLatch(serverResponseMap.size());
-
+    Future<Void>[] futures = new Future[serverResponseMap.size()];
+    // based on ideas from on https://stackoverflow.com/questions/19348248/waiting-on-a-list-of-future
+    // mostly because we need to handle and transfer the exception in threads into caller thread.
+    ExecutorCompletionService<Void> countDownHelper = new ExecutorCompletionService<>(executorService);

Review comment:
       wouldn't `CompletableFuture.allOf` satisfy your requirement here - https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html#allOf-java.util.concurrent.CompletableFuture...- ?
   Or is it too invasive change to replace `Future` with `CompletableFuture`?




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