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

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

richardstartin commented on a change in pull request #8272:
URL: https://github.com/apache/pinot/pull/8272#discussion_r817701130



##########
File path: pinot-core/src/main/java/org/apache/pinot/core/query/reduce/StreamingReduceService.java
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@@ -106,15 +104,18 @@ public BrokerResponseNative reduceOnStreamResponse(BrokerRequest brokerRequest,
     return brokerResponseNative;
   }
 
-  private static void processIterativeServerResponse(StreamingReducer reducer, ExecutorService executorService,
+  @VisibleForTesting
+  static void processIterativeServerResponse(StreamingReducer reducer,
       Map<ServerRoutingInstance, Iterator<Server.ServerResponse>> serverResponseMap, long reduceTimeOutMs,
-      ExecutionStatsAggregator aggregator) throws Exception {
+      ExecutionStatsAggregator aggregator)
+      throws Exception {
     int cnt = 0;
-    Future[] futures = new Future[serverResponseMap.size()];
-    CountDownLatch countDownLatch = new CountDownLatch(serverResponseMap.size());
-
-    for (Map.Entry<ServerRoutingInstance, Iterator<Server.ServerResponse>> entry: serverResponseMap.entrySet()) {
-      futures[cnt++] = executorService.submit(() -> {
+    CompletableFuture<Void>[] futures = new CompletableFuture[serverResponseMap.size()];
+    // based on ideas from on https://stackoverflow.com/questions/19348248/waiting-on-a-list-of-future
+    // and https://stackoverflow.com/questions/23301598/transform-java-future-into-a-completablefuture
+    // Future created via ExecutorService.submit() can be created by CompletableFuture.supplyAsync()
+    for (Map.Entry<ServerRoutingInstance, Iterator<Server.ServerResponse>> entry : serverResponseMap.entrySet()) {
+      futures[cnt++] = CompletableFuture.supplyAsync(() -> {

Review comment:
       This executes in a global pool which isn't the right behaviour. You can supply an executor to make it execute in the allotted thread pool.




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