SeekableAsyncFile

This library will provide a SeekableAsyncFile struct that is designed to be similar in function to tokio::fs::File. It provides async read_at and write_at methods, which aren't currently available with Tokio.

The target platform must support std::os::unix::fs::FileExt.

Getting started

Add it to your project like:

cargo add seekable-async-file

View the documentation for usage guides.

Delayed sync

The write_at_with_delayed_sync method is provided to call write and fdatasync, but the sync call will be made at some future time. The returned future won't resolve until the sync call is made and completes successfully. This is a performance optimisation to try to batch multiple writes with a single sync, but still keep the semantics where the call completes only when successfully written to disk.

If this is used, make sure to also execute the start_delayed_data_sync_background_loop method in the background, such as using tokio::spawn or tokio::join!.

Metrics

Metrics will be populated via the SeekableAsyncFileMetrics struct. All values are atomic, so it's possible to read them at any time from any thread safely using the provided getter methods. This is designed for use inside a larger system (e.g. database, object storage, cache) or I/O subsystem.

Features

For experimental purposes, there are other Cargo features that can be toggled:

• fsync_delayed: (Default) Delay calls to fdatasync when using write_at_with_delayed_sync.
• fsync_immediate: Immediately call fdatasync, even from write_at_with_delayed_sync. The start_delayed_data_sync_background_loop method does nothing.
• mmap: Use mmap instead of pread and pwrite.
• tokio_file: (Default) Use pread and pwrite with tokio::spawn_blocking.
• unsafe_fsync_none: (UNSAFE) Never call fdatasync, even when expected to.