Struct SharedRow

pub struct SharedRow(Row);

A thread-local row, which can be borrowed and returned.

Example

Use this type instead of creating a new row:

use mz_repr::SharedRow;

let mut row_builder = SharedRow::get();

This allows us to reuse an existing row allocation instead of creating a new one or retaining an allocation locally. Additionally, we can observe the size of the local row in a central place and potentially reallocate to reduce memory needs.

Panic

SharedRow::get panics when trying to obtain multiple references to the shared row.

Tuple Fields

0: Row

Implementations

impl SharedRow

const SHARED_ROW: LocalKey<Cell<Option<Row>>>

A thread-local slot containing a shared Row that can be temporarily used by a function. There can be at most one active user of this Row, which is tracked by the state of the Option<_> wrapper. When it is Some(..), the row is available for using. When it is None, it is not, and the constructor will panic if a thread attempts to use it.

pub fn get() -> Self

Get the shared row.

The row’s contents are cleared before returning it.

Panic

Panics when the row is already borrowed elsewhere.

pub fn pack<'a, I, D>(iter: I) -> Row

where I: IntoIterator<Item = D>, D: Borrow<Datum<'a>>,

Gets the shared row and uses it to pack iter.

Methods from Deref<Target = Row>

const SIZE: usize = 23usize

pub fn decode_from_proto( &mut self, proto: &ProtoRow, desc: &RelationDesc, ) -> Result<(), String>

A variant of Row::from_proto that allows for reuse of internal allocs and validates the decoding against a provided RelationDesc.

pub fn packer(&mut self) -> RowPacker<'_>

Constructs a RowPacker that will pack datums into this row’s allocation.

This method clears the existing contents of the row, but retains the allocation.

pub fn pack_using<'a, I, D>(&mut self, iter: I) -> Row

where I: IntoIterator<Item = D>, D: Borrow<Datum<'a>>,

Use self to pack iter, and then clone the result.

This is a convenience method meant to reduce boilerplate around row formation.

pub fn byte_len(&self) -> usize

Returns the total amount of bytes used by this row.

pub fn data_len(&self) -> usize

The length of the encoded row in bytes. Does not include the size of the Row struct itself.

pub fn byte_capacity(&self) -> usize

Returns the total capacity in bytes used by this row.

pub fn as_row_ref(&self) -> &RowRef

Extracts a Row slice containing the entire Row.

fn clear(&mut self)

Clear the contents of the Row, leaving any allocation in place.

Methods from Deref<Target = RowRef>

pub fn unpack(&self) -> Vec<Datum<'_>>

Unpack self into a Vec<Datum> for efficient random access.

pub fn unpack_first(&self) -> Datum<'_>

Return the first Datum in self

Panics if the RowRef is empty.

pub fn iter(&self) -> DatumListIter<'_>

Iterate the Datum elements of the RowRef.

pub fn byte_len(&self) -> usize

Return the byte length of this RowRef.

pub fn data(&self) -> &[u8]

For debugging only.

pub fn is_empty(&self) -> bool

True iff there is no data in this RowRef.

Trait Implementations

impl Debug for SharedRow

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

Formats the value using the given formatter.

impl Deref for SharedRow

type Target = Row

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl DerefMut for SharedRow

fn deref_mut(&mut self) -> &mut Self::Target

Mutably dereferences the value.

impl Drop for SharedRow

fn drop(&mut self)

Executes the destructor for this type.