[GitHub] [incubator-pinot] mqliang commented on a change in pull request #6678: Extends GroupByCombineOperator and GroupByOrderByCombineOperator from BaseCombineOperator

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

mqliang commented on a change in pull request #6678:
URL: https://github.com/apache/incubator-pinot/pull/6678#discussion_r593385265



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File path: pinot-core/src/main/java/org/apache/pinot/core/operator/combine/BaseCombineOperator.java
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@@ -52,77 +52,102 @@
   protected final ExecutorService _executorService;
   protected final long _endTimeMs;
 
+  protected final int _numOperators;
+  protected int _numThreads;
+  // Use a Phaser to ensure all the Futures are done (not scheduled, finished or interrupted) before the main thread
+  // returns. We need to ensure this because the main thread holds the reference to the segments. If a segment is
+  // deleted/refreshed, the segment will be released after the main thread returns, which would lead to undefined
+  // behavior (even JVM crash) when processing queries against it.
+  protected final Phaser _phaser = new Phaser(1);
+  protected final Future[] _futures;
+  // Use a _blockingQueue to store the per-segment result
+  private final BlockingQueue<IntermediateResultsBlock> _blockingQueue;
+
   public BaseCombineOperator(List<Operator> operators, QueryContext queryContext, ExecutorService executorService,
       long endTimeMs) {
     _operators = operators;
     _queryContext = queryContext;
     _executorService = executorService;
     _endTimeMs = endTimeMs;
+    _numOperators = _operators.size();
+    _numThreads = CombineOperatorUtils.getNumThreadsForQuery(_numOperators);

Review comment:
       I add a new constructor at L78, which can accept a `numThreads` parameter from subclass. GroupByCombineOperator and GroupByOrderByCombineOperator are now using the new constructor 




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