Summary:
This PR adds support for new APIs Async Read that reads the data
asynchronously and Poll API that checks if requested read request has
completed or not.
Usage: In RocksDB, we are currently planning to prefetch data
asynchronously during sequential scanning and RocksDB will call these
APIs to prefetch more data in advanced.
Design:
- ReadAsync API submits the read request to underlying FileSystem in
order to read data asynchronously. When read request is completed,
callback function will be called. cb_arg is used by RocksDB to track the
original request submitted and IOHandle is used by FileSystem to keep track
of IO requests at their level.
- The Poll API is added in FileSystem because the call could end up handling
completions for multiple different files which is not specific to a
FSRandomAccessFile instance. There could be multiple outstanding file reads
from different files in future and they can complete in any order.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9564
Test Plan: Test will be added in separate PR.
Reviewed By: anand1976
Differential Revision: D34226216
Pulled By: akankshamahajan15
fbshipit-source-id: 95e64edafb17f543f7232421d51e2665a3267f69
Akanksha Mahajan
559525dcbb