[GitHub] [arrow] westonpace commented on a change in pull request #11923: ARROW-14970: [C++] Make ExecNodes can generate/consume tasks

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

westonpace commented on a change in pull request #11923:
URL: https://github.com/apache/arrow/pull/11923#discussion_r767079966



##########
File path: cpp/src/arrow/compute/exec/exec_plan.h
##########
@@ -226,6 +227,8 @@ class ARROW_EXPORT ExecNode {
   std::string ToString() const;
 
  protected:
+  static inline Result<ExecBatch> IdentityTask(ExecBatch batch) { return batch; }
+

Review comment:
       This isn't really a task though is it.  I was expecting something like...
   
   ```
   static inline std::function<Result<ExecBatch>(ExecBatch)> IdentityTask() { return [] (ExecBatch batch) { return batch; }; }
   ```

##########
File path: cpp/src/arrow/compute/exec/exec_plan.h
##########
@@ -134,8 +134,9 @@ class ARROW_EXPORT ExecNode {
   /// - these are allowed to call back into PauseProducing(), ResumeProducing()
   ///   and StopProducing()
 
-  /// Transfer input batch to ExecNode
-  virtual void InputReceived(ExecNode* input, ExecBatch batch) = 0;
+  /// Transfer the input task to ExecNode
+  virtual void InputReceived(ExecNode* input, ExecBatch batch,
+                             std::function<Result<ExecBatch>(ExecBatch)> task) = 0;

Review comment:
       I would expect the signature to be:
   
   ```
   virtual void InputReceived(ExecNode* input, std::function<Result<ExecBatch>(ExecBatch)> task) = 0;
   ```
   
   I'm not sure what it means to have `batch` and `task`?
   
   Is this some kind of intermediate step between the two models?




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