huberylee commented on code in PR #39393:
URL: https://github.com/apache/arrow/pull/39393#discussion_r1446277356
##########
cpp/src/arrow/io/buffered.h:
##########
@@ -163,5 +164,156 @@ class ARROW_EXPORT BufferedInputStream
std::unique_ptr<Impl> impl_;
};
+/// \class ChunkBufferedInputStream
+/// \brief An ChunkBufferedInputStream that performs buffered reads from an
+/// unbuffered InputStream, which can mitigate the overhead of many small
+/// reads in some cases.
+///
+/// When an actual io request occurs, read ranges will be coalesced if the
+/// distance between them is less than io_merge_threshold, and the actual size
+/// in one io request will be limited by the buffer_size.
+///
+/// \attention It is important to note that since the data returned by the Read
+/// interface is a reference to the Buffer, the caller must ensure that the
data
+/// returned by the Read interface is processed completely before calling the
+/// Read interface again. Otherwise, fatal errors may occur due to data in the
+/// Buffer being overwritten.
+class ARROW_EXPORT ChunkBufferedInputStream : public InputStream {
+ public:
+ static Result<std::shared_ptr<ChunkBufferedInputStream>> Create(
+ int64_t start, int64_t length, std::shared_ptr<RandomAccessFile> impl,
+ std::vector<ReadRange> read_ranges, int64_t buffer_size, int32_t
io_merge_threshold,
+ MemoryPool* pool_ = ::arrow::default_memory_pool());
+
+ // InputStream interface
+ Status Advance(int64_t nbytes) override;
+
+ /// \brief Peek some data without advancing the read position.
+ Result<std::string_view> Peek(int64_t nbytes) override;
+
+ // Readable interface
+ Result<int64_t> Read(int64_t nbytes, void* out) override;
+
+ Result<std::shared_ptr<Buffer>> Read(int64_t nbytes) override;
+
+ // FileInterface
+ Status Close() override;
+
+ Result<int64_t> Tell() const override;
+
+ bool closed() const override;
+
+ private:
+ explicit ChunkBufferedInputStream(int64_t start, int64_t length,
+ std::shared_ptr<RandomAccessFile> impl,
+ std::vector<ReadRange> read_ranges,
+ int64_t buffer_size, int32_t
io_merge_threshold,
+ std::shared_ptr<ResizableBuffer> buffer);
+
+ inline Status CheckClosed() const {
+ if (ARROW_PREDICT_TRUE(is_open_)) {
+ return Status::OK();
+ }
+
+ return Status::IOError("Operation forbidden on closed file input stream");
+ }
+
+ inline Status CheckReadRange(int64_t nbytes) {
+ // Upon reaching the end of the current read range, if there is a next read
+ // range, current_range_available_bytes_ will be set to the length of the
+ // next read range, and this will be ensured by ConsumeBuffer;
+ if (ARROW_PREDICT_TRUE(current_range_available_bytes_ >= nbytes)) {
+ return Status::OK();
+ }
+
+ if (current_range_available_bytes_ > 0 && current_range_available_bytes_ <
nbytes) {
+ if (read_ranges_[read_ranges_idx_].length > nbytes) {
+ return Status::IOError("Read length is illegal");
+ }
+
+ // At the beginning of a new read range and required bytes is more than
+ // read range length, we think it's ok because there are some tentative
+ // read requests when getting next page data.
+ return Status::OK();
+ }
+
+ if (read_ranges_idx_ != read_ranges_.size()) {
Review Comment:
> Why not checking this before line 230?
We can not check this before line 230 for there may be more ranges to read.
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