[jira] [Created] (ARROW-11943) [C++] Create specialized queue for serial readahead

["Weston Pace (Jira)" <ji...@apache.org>]

Weston Pace created ARROW-11943:
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             Summary: [C++] Create specialized queue for serial readahead
                 Key: ARROW-11943
                 URL: https://issues.apache.org/jira/browse/ARROW-11943
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++
            Reporter: Weston Pace


Follow-up from ARROW-11590.

The current serial readahead implementation is a little confusing.

Problem 1:

The readahead operator is keeping track of the queue size instead of the queue.  This is because the queue is intended more for either the "fill up queue then spin until free" case or the "fill up queue and then drop on the floor" case and not the "fill up queue and then stop reading values" case.

In particular, ProducerConsumerQueue::Write should return true if the write filled up the queue and ProducerConsumerQueue::Read should return true if the read made space in an otherwise empty queue.  This would need to be atomic/thread-safe so every true returned from a ::Write should be paired exactly 1:1 with a true-returning ::Read

Problem 2:

Serial readahead's writes follow a write slot to queue, get value, put value in slot pattern.  Currently this uses a shared_ptr.  This could probably be changed to use util::optional if we created a BackPtr function in the queue.

These two changes would simplify the serial readahead logic and help keep the code organized.



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