moli/moli-disk-pool

moli-disk-pool

Thread-safe storage for multiple resources in one anonymous temporary file. Moli shares a pool between parkable images and generic response bodies.

What it does

• Stores each payload in an immutable (offset, len) extent. Reservations and stored-data handles keep the pool alive and return their space when dropped.
• Reuses free extents with exact-fit, then worst-fit allocation, merging adjacent holes on release. Offset and size indexes make allocation and release O(log F) for F free extents.
• Provides offset-based reads and writes using standard platform file APIs. The file is created with tempfile; no positioned_io dependency is needed.

Trade-offs

• One file avoids a separate file per resource. The two indexes cost extra metadata, and fragmentation can still prevent a contiguous allocation.
• Released space is reusable, but the file is not compacted or truncated. The optional capacity limit bounds the logical high-water mark, not guaranteed filesystem space.
• I/O is synchronous; async callers must arrange blocking execution. Storage failures are returned to the caller, which owns any memory fallback.
• This is temporary backing storage, not a persistent cache. It provides no URL index, deduplication, or durability guarantee.

Examples

• basic.rs: write, read a range, and reuse an extent.
• capacity.rs: handle capacity exhaustion and cancel a reservation.
• shared_readers.rs: share stored data across threads.

Run from the repository root:

cargo run -p moli-disk-pool --example basic
cargo run -p moli-disk-pool --example capacity
cargo run -p moli-disk-pool --example shared_readers