aucahuasi commented on code in PR #14226:
URL: https://github.com/apache/arrow/pull/14226#discussion_r996434037
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cpp/src/parquet/arrow/reader.cc:
##########
@@ -1107,8 +1112,13 @@ class RowGroupGenerator {
if (!reader->properties().pre_buffer()) {
row_group_read = SubmitRead(cpu_executor_, reader, row_group,
column_indices);
} else {
+ reader->parquet_reader()->PreBuffer({row_group}, column_indices_,
+ reader_properties_.io_context(),
+ reader_properties_.cache_options());
auto ready = reader->parquet_reader()->WhenBuffered({row_group},
column_indices);
if (cpu_executor_) ready = cpu_executor_->TransferAlways(ready);
+ // wait for buffering the rowgroup before read it
+ ready.Wait();
Review Comment:
I think that when we transfer the future, the `PreBuffer` that it's running
now (in a different thread) cannot finish before the future triggers
`ReadOneRowGroup` (because the future was already transferred into a different
thread)
So perhaps we just need a way to make sure `PreBuffer` gets called before
in the same thread of the future.
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