pitrou commented on code in PR #37460:
URL: https://github.com/apache/arrow/pull/37460#discussion_r1310200589
##########
cpp/src/arrow/io/buffered.cc:
##########
@@ -373,33 +378,35 @@ class BufferedInputStream::Impl : public BufferedBase {
return Status::Invalid("Bytes to read must be positive. Received:",
nbytes);
}
- if (nbytes < buffer_size_) {
- // Pre-buffer for small reads
- RETURN_NOT_OK(BufferIfNeeded());
+ // 1. First consume pre-buffered data.
+ int64_t pre_buffer_copy_bytes = std::min(nbytes, bytes_buffered_);
+ if (pre_buffer_copy_bytes > 0) {
+ memcpy(out, buffer_data_ + buffer_pos_, pre_buffer_copy_bytes);
+ ConsumeBuffer(pre_buffer_copy_bytes);
+ }
+ int64_t remain_bytes = nbytes - pre_buffer_copy_bytes;
Review Comment:
Nit: call this `remaining_bytes`
##########
cpp/src/arrow/io/buffered.cc:
##########
@@ -373,33 +378,35 @@ class BufferedInputStream::Impl : public BufferedBase {
return Status::Invalid("Bytes to read must be positive. Received:",
nbytes);
}
- if (nbytes < buffer_size_) {
- // Pre-buffer for small reads
- RETURN_NOT_OK(BufferIfNeeded());
+ // 1. First consume pre-buffered data.
Review Comment:
Should you first ensure that `nbytes` does not go past `raw_read_bound_`?
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