[GitHub] [arrow] pitrou commented on a change in pull request #7030: ARROW-7808: [Java][Dataset] Implement Dataset Java API by JNI to C++

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

pitrou commented on a change in pull request #7030:
URL: https://github.com/apache/arrow/pull/7030#discussion_r552554266



##########
File path: cpp/src/arrow/memory_pool.h
##########
@@ -149,6 +149,43 @@ class ARROW_EXPORT ProxyMemoryPool : public MemoryPool {
   std::unique_ptr<ProxyMemoryPoolImpl> impl_;
 };
 
+class ARROW_EXPORT ReservationListener {
+ public:
+  virtual ~ReservationListener();
+
+  virtual Status OnReservation(int64_t size) = 0;
+  virtual Status OnRelease(int64_t size) = 0;
+
+ protected:
+  ReservationListener();
+};
+
+class ARROW_EXPORT ReservationListenableMemoryPool : public MemoryPool {

Review comment:
       What does "ReservationListenableMemoryPool" mean? What does "pre-reserving" mean? How does this even work, since you're delegating actual allocations to a regular MemoryPool?




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