Struct IdentityValues

pub(crate) struct IdentityValues {
    free: Vec<(u32, u32)>,
    next_index: u32,
    count: usize,
    id_source: IdSource,
}

A simple structure to allocate Id identifiers.

Calling alloc returns a fresh, never-before-seen id. Calling release marks an id as dead; it will never be returned again by alloc.

IdentityValues returns Ids whose index values are suitable for use as indices into a Vec<T> that holds those ids’ referents:

• Every live id has a distinct index value. Every live id’s index selects a distinct element in the vector.

• IdentityValues prefers low index numbers. If you size your vector to accommodate the indices produced here, the vector’s length will reflect the highwater mark of actual occupancy.

• IdentityValues reuses the index values of freed ids before returning ids with new index values. Freed vector entries get reused.

• The non-reuse property is achieved by storing an epoch alongside the index in an Id. Index values are reused, but only with a different epoch.

IdentityValues can also be used to track the count of IDs allocated by some external allocator. Combining internal and external allocation is not allowed; calling both alloc and mark_as_used on the same IdentityValues will result in a panic. The external mode is used when playing back a trace of wgpu operations.

Fields

free: Vec<(u32, u32)>

next_index: u32

count: usize

id_source: IdSource

Implementations

impl IdentityValues

pub fn alloc<T: Marker>(&mut self) -> Id<T>

Allocate a fresh, never-before-seen ID.

Panics

If mark_as_used has previously been called on this IdentityValues.

pub fn mark_as_used<T: Marker>(&mut self, id: Id<T>) -> Id<T>

Increment the count of used IDs.

Panics

If alloc has previously been called on this IdentityValues.

pub fn release<T: Marker>(&mut self, id: Id<T>)

Free id and/or decrement the count of used IDs.

Freed IDs will never be returned from alloc again.

pub fn count(&self) -> usize

Trait Implementations

impl Debug for IdentityValues

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

Formats the value using the given formatter.