Re: [PR] GH-39377: [C++] IO: Reuse same buffer in CompressedInputStream [arrow]

[via GitHub]

mapleFU commented on code in PR #39807:
URL: https://github.com/apache/arrow/pull/39807#discussion_r1471298716


##########
cpp/src/arrow/io/compressed.cc:
##########
@@ -261,21 +262,39 @@ class CompressedInputStream::Impl {
     }
   }
 
-  bool closed() { return !is_open_; }
+  bool closed() const { return !is_open_; }
 
   Result<int64_t> Tell() const { return total_pos_; }
 
   // Read compressed data if necessary
   Status EnsureCompressedData() {
     int64_t compressed_avail = compressed_ ? compressed_->size() - 
compressed_pos_ : 0;
     if (compressed_avail == 0) {
+      // Ensure compressed_ buffer is allocated with kChunkSize.
+      if (compressed_ == nullptr) {
+        ARROW_ASSIGN_OR_RAISE(compressed_, AllocateResizableBuffer(kChunkSize, 
pool_));
+      } else {
+        RETURN_NOT_OK(compressed_->Resize(kChunkSize, 
/*shrink_to_fit=*/false));
+      }
       // No compressed data available, read a full chunk
-      ARROW_ASSIGN_OR_RAISE(compressed_, raw_->Read(kChunkSize));
+      ARROW_ASSIGN_OR_RAISE(int64_t read_size,
+                            raw_->Read(kChunkSize, 
compressed_->mutable_data_as<void>()));

Review Comment:
   Aha we have a `supports_zero_copy()`, can we use this to optimize it?



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