Struct SlotCache 

pub struct SlotCache<const N: usize> { /* private fields */ }

Available on crate feature fs only.

Bounded LRU image cache backed by a fixed-size array.

Const-generic parameter

N is the number of slots. Choose a value appropriate to the platform’s available RAM: on the STM32H747I-DISCO a value of 8–16 is typical.

Eviction policy

On insertion when all N slots are occupied, the slot with the smallest (oldest) ts value is evicted. On a cache hit, the matching slot’s ts is updated to the current counter value and the counter increments.

Determinism

Given a fixed sequence of get/insert calls starting from a freshly constructed SlotCache, the eviction order is fully deterministic. Tests that require reproducible cache behaviour should create a fresh SlotCache::new() and drive calls in a known order.

Handle numbering

CacheHandle values are assigned sequentially starting at 1 (0 is reserved). Within a session handles are never reused.

Implementations

impl<const N: usize> SlotCache<N>

pub const fn new() -> Self

Create an empty cache with all slots vacant.

pub fn get(&mut self, handle: CacheHandle) -> Option<&ImageDescriptor<'static>>

Look up handle in the cache.

On a hit the slot’s timestamp is updated (LRU touch) and a reference to the cached ImageDescriptor is returned. On a miss None is returned.

pub fn insert(&mut self, descriptor: ImageDescriptor<'static>) -> CacheHandle

Insert descriptor into the cache and return its CacheHandle.

If all slots are occupied, the least-recently-used entry is evicted first. The returned handle is unique within the session.

pub fn evict(&mut self, handle: CacheHandle)

Evict the entry identified by handle if it is present.

After eviction the decoded pixels are dropped. The next resolve_image call for the same asset will re-decode from the source.

pub fn len(&self) -> usize

Return the number of occupied slots.

pub fn is_empty(&self) -> bool

Return true if no slots are occupied.

Trait Implementations

impl<const N: usize> Default for SlotCache<N>

fn default() -> Self

Returns the “default value” for a type.

impl<const N: usize> ImageCache<'static> for SlotCache<N>

fn get(&self, _handle: CacheHandle) -> Option<&ImageDescriptor<'static>>

Return the descriptor associated with handle, if it is still cached.

fn put(&mut self, descriptor: ImageDescriptor<'static>) -> CacheHandle

Register descriptor with the cache and return its handle.