Struct BlockCache 

pub struct BlockCache<R> { /* private fields */ }

Available on crate feature std only.

A ReadAt wrapper that keeps recently read blocks in memory.

The source is read in fixed-size blocks, held within a byte budget across sharded locks and evicted with the CLOCK algorithm. A read that spans blocks is assembled from them. Reads larger than a quarter of the budget go straight to the source so one large read cannot flush the cache.

The cache assumes the source does not change: the size is captured at construction and cached blocks are never revalidated. Wrap a new cache around a new source when the source is replaced.

Implementations

impl<R> BlockCache<R>

where R: ReadAt,

pub fn new(inner: R, config: &BlockCacheConfig) -> Result<BlockCache<R>, Error>

Wrap inner, capturing its current size.

Errors

Returns the error of ReadAt::size on inner.

pub fn get_ref(&self) -> &R

The wrapped source.

pub fn len(&self) -> u64

The size of the source captured at construction.

pub fn is_empty(&self) -> bool

Whether the source was empty at construction.

pub fn is_enabled(&self) -> bool

Whether blocks are kept at all (the budget holds at least one block).

pub fn block_size(&self) -> usize

The size of one block.

pub fn block(&self, index: u64) -> Result<Bytes, Error>

The block with index index, shorter than the block size only at the end of the source.

A cached block is returned without copying. With caching disabled the block is read from the source on every call.

Errors

Returns io::ErrorKind::UnexpectedEof for a block past the captured size, or the error of the source.

Trait Implementations

impl<R> Debug for BlockCache<R>

where R: Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<R> ReadAt for BlockCache<R>

where R: ReadAt,

fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<(), Error>

Fill all of buf with the bytes starting at offset.

fn size(&self) -> Result<u64, Error>

The current size of the source in bytes.