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Adopt completed image buffers, protect readers with snapshots, and park encoded bytes into one disk extent with a reusable backup. Keep resident and parked registries separate, expose owner-driven deadlines and force parking, and synchronize notifications with a short-lock waiting flag. Include lifecycle, concurrency, scheduling, and failure regressions with documentation and runnable examples.
moli-parkable-image
Shared storage for completed encoded image bytes.
It releases idle buffers from memory by parking them in moli-disk-pool, then restores them when a reader needs them.
The renderer shares this backing between image consumers and network records.
What it does
from_frozen_bytes(Vec<u8>)takes ownership of a completed buffer. Snapshots provide read-only access and prevent its memory from being discarded while readers are active.- Parking writes one extent per image. Reading a parked image restores its bytes; the disk backup remains, so parking again needs no additional write.
- A manager tracks deadlines and separates resident from parked images. Defaults are a 1 KiB minimum size, a 30-second initial delay, and a 2-second delay after the last snapshot is released.
park_images()respects those delays;force_park_images()bypasses them and immediately retries parking. Neither waits for a deadline or discards bytes held by live snapshots.- The owning runtime drives scheduling. This crate creates no threads or timers; constructing a manager alone does not start automatic parking.
Trade-offs
Arc<Vec<u8>>adopts the receive buffer without a full payload copy, but retains its spare capacity until parking.- Only completed encoded bytes are managed. Receive buffers and decoded RGBA/SVG data remain outside this crate.
- Unparking synchronously reads the whole image, even for a partial read. Retaining the disk backup uses space but makes later parking cheap.
- Failed parking keeps the bytes in memory; failed unparking returns an I/O error. Releasing a heap buffer does not guarantee an immediate RSS reduction, particularly with allocator retention or tmpfs.
Examples
These use synthetic bytes; no decoder is involved.
park_unpark.rs: park manually, then restore through a snapshot.reader_leases.rs: show why snapshots prevent parking but cloned image handles do not.deadline.rs: customize the policy and drive one deadline. This is a single-threaded demonstration, not a concurrent scheduler.
Run from the repository root:
cargo run -p moli-parkable-image --example park_unpark
cargo run -p moli-parkable-image --example reader_leases
cargo run -p moli-parkable-image --example deadline