Struct Segment 

pub struct Segment { /* private fields */ }

A segment’s entries in memory, plus whether they differ from the file they were read from.

super holds one of these per process for the segment this application writes, and one for the read-only segment a bundle ships. cn export owns a third directly: the segment it warms into a bundle is one this process never reads back, so it is built and written as a value rather than through the process-global tiers.

Implementations

impl Segment

pub fn read_from(path: &Path) -> Self

Read path into memory. An absent, unreadable, or foreign file reads as an empty segment: whatever it held is regenerated, and the next write replaces it.

pub fn get(&mut self, kind: CacheEntryKind, key: &str) -> Option<&[u8]>

The bytes stored for key, or None when the segment holds no such entry. Marks the entry used, so a flush does not evict what this run is running on.

pub fn put(&mut self, kind: CacheEntryKind, key: &str, bytes: &[u8]) -> bool

Take bytes as key’s entry, reporting whether the segment took them.

An entry already holding at least as many bytes is left alone. Growth is the only reliable “new content” signal for a driver pipeline blob, which only accumulates but does not serialize deterministically (MoltenVK shuffles entry order run to run), so a byte compare would dirty the segment every launch. A content-addressed artifact re-stored under its own key is by definition the bytes already there.

pub fn write_to(&mut self, path: &Path, budget: u64) -> bool

Replace path with what the segment now holds, first evicting entries until its payload fits budget. Reports whether the file was written.

A segment nothing changed is not rewritten: this is where the per-store growth check pays off, since a launch that only read the cache leaves the file untouched.