Function read_cache 

pub fn read_cache<const FULL_ROUNDS: usize, G, Srs>(
    identifier: &str,
    path: &Path,
    srs: Arc<Srs>,
) -> Result<MmapProverIndex<FULL_ROUNDS, G, Srs>, CacheError>
where
    G: KimchiCurve<FULL_ROUNDS>,
    Srs: SRS<G>,
    G::BaseField: PrimeField,

Reads a cache file produced by write_cache and returns an MmapProverIndex: a ProverIndex-compatible wrapper whose bulk Vec<F> fields are backed by the mmap’d file rather than heap copies.

Reading is a single mmap(2) syscall; the prover reads field elements directly from page-cache pages which the kernel can evict under memory pressure and re-fault on demand. This is the “OS can evict cached keys” behaviour the cache was designed for.

The returned MmapProverIndex [Deref]s to &ProverIndex, so existing callers that pass &ProverIndex<...> into the prover continue to work unchanged.

Safety of the construction

This function constructs Vec<F> values via Vec::from_raw_parts(mmap_ptr, len, len), pointing directly into the mmap. Those Vecs are bound by the lifetime of the mmap — which MmapProverIndex guarantees by holding an Arc<ReadOnlyMmap> alongside the wrapped index, and by wrapping the inner ProverIndex in ManuallyDrop so Vec::drop can never run on them. See the docstring on MmapProverIndex for the full invariant.

Identifier and ark-ff version must match the values the file was produced with, otherwise a descriptive error is returned.