PuduLangMediator.Utils.Shared

type: module path: "@root/src/PuduLangMediator/Utils/Shared.pudu" fidelity: Active grammar: "[[grammar/pudu]]" depth_score: 0.7 depth_status: DEEP tags: [module, leaf] aliases: [PuduLangMediator.Utils.Shared]

Purpose

A value shared between threads that changes only under its lock, so every read-modify-write is atomic.

Interface

Signatures

export type Shared[S] = { lock: Sync.Mutex, held: Sync.Cell[S] }

export fn shared[S](initial: S) -> Shared[S]

export fn current[S](source: &Shared[S]) -> S

export fn change[S, R](target: &Shared[S], step: fn(S) -> (S, R)) -> R

export fn update[S](target: &Shared[S], step: fn(S) -> S) -> ()

Linkage

• Requires: standard library only.
• Consumed by: [[src/PuduLangMediator/Behaviors/Logging]], [[src/PuduLangMediator/Context]], [[src/PuduLangMediator/Mediator]].

Algorithm

1. change reads, computes, and writes under the mutex and answers the second half of what the step returned.
2. update is change with no answer.

Negative Logic (Prohibited Paths)

• No write depends on a read made outside the lock.

Edge Cases

• A poisoned lock or cell stops the program: shared state that cannot be read is not recoverable here.

Depth

DEPTH 0.7 (DEEP). Tested by the suite mirroring this module under test/.

Grill Log

• Q: Why a mutex around the cell rather than the cell alone? A: A cell makes single reads and writes atomic, not a read followed by a write; concurrent updates would be lost. _Rejected:_ a bare Sync.Cell (lost updates under contention).

Referenced by

[[grammar/pudu]] · [[src/PuduLangMediator/Behaviors/Logging]] · [[src/PuduLangMediator/Context]] · [[src/PuduLangMediator/Mediator]] · [[src/PuduLangMediator/Utils/_MOC]]