[GitHub] [arrow] westonpace commented on a diff in pull request #35902: GH-35837: [C++] Acero will hang if StopProducing is called while backpressure is applied on the source node

["westonpace (via GitHub)" <gi...@apache.org>]

westonpace commented on code in PR #35902:
URL: https://github.com/apache/arrow/pull/35902#discussion_r1221598762


##########
cpp/src/arrow/acero/source_node.cc:
##########
@@ -263,6 +263,22 @@ struct SourceNode : ExecNode, public TracedNode {
     to_finish.MarkFinished();
   }
 
+  Status StopProducing() override {
+    // GH-35837: ensure node is not paused
+    Future<> to_finish;
+    {
+      std::lock_guard<std::mutex> lg(mutex_);
+      if (!backpressure_future_.is_finished()) {

Review Comment:
   If the backpressure future is not finished then backpressure is currently applied.  It's basically...
   
   ```
   void ResumeProducing() {
     if (actually_paused) {
       ... // unpause
     }
   }
   ```



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