Struct heed::ReservedSpace

pub struct ReservedSpace<'a> { /* private fields */ }

A structure that is used to improve the write speed in LMDB.

You must write the exact amount of bytes, no less, no more.

Implementations

impl ReservedSpace<'_>

pub fn size(&self) -> usize

The total number of bytes that this memory buffer has.

pub fn remaining(&self) -> usize

The remaining number of bytes that this memory buffer has.

pub fn written_mut(&mut self) -> &mut [u8]

Get a slice of all the bytes that have previously been written.

This can be used to write information which cannot be known until the very end of serialization. For example, this method can be used to serialize a value, then compute a checksum over the bytes, and then write that checksum to a header at the start of the reserved space.

pub fn fill_zeroes(&mut self)

Fills the remaining reserved space with zeroes.

This can be used together with written_mut to get a mutable view of the entire reserved space.

Note

After calling this function, the entire space is considered to be filled and any further attempt to write anything else will fail.

pub fn as_uninit_mut(&mut self) -> &mut [MaybeUninit<u8>]

Get a slice of bytes corresponding to the entire reserved space.

It is safe to write to any byte within the slice. However, for a write past the end of the prevously written bytes to take effect, assume_written has to be called to mark those bytes as initialized.

Safety

As the memory comes from within the database itself, the bytes may not yet be initialized. Thus, it is up to the caller to ensure that only initialized memory is read (ensured by the MaybeUninit API).

pub unsafe fn assume_written(&mut self, len: usize)

Marks the bytes in the range 0..len as being initialized by advancing the internal write pointer.

Safety

The caller guarantees that all bytes in the range have been initialized.

Trait Implementations

impl Debug for ReservedSpace<'_>

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

Formats the value using the given formatter.

impl Seek for ReservedSpace<'_>

Note

May only seek within the previously written space. Attempts to do otherwise will result in an error.

fn seek(&mut self, pos: SeekFrom) -> Result<u64>

Seek to an offset, in bytes, in a stream.

fn rewind(&mut self) -> Result<()>

Rewind to the beginning of a stream.

fn stream_position(&mut self) -> Result<u64>

Returns the current seek position from the start of the stream.

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

🔬This is a nightly-only experimental API. (seek_stream_len)

Returns the length of this stream (in bytes).

fn seek_relative(&mut self, offset: i64) -> Result<(), Error>

Seeks relative to the current position.

impl Write for ReservedSpace<'_>

fn write(&mut self, buf: &[u8]) -> Result<usize>

Writes a buffer into this writer, returning how many bytes were written.

fn write_all(&mut self, buf: &[u8]) -> Result<()>

Attempts to write an entire buffer into this writer.

fn flush(&mut self) -> Result<()>

Flushes this output stream, ensuring that all intermediately buffered contents reach their destination.

fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize, Error>

Like write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Writer has an efficient write_vectored implementation.

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error>

🔬This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer.

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

Writes a formatted string into this writer, returning any error encountered.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Write.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 32 bytes