Struct WaitingList 

pub struct WaitingList { /* private fields */ }

Coordination layer for pub-sub message delivery.

Combines persistent storage (EntryRepository) with in-memory waiter channels. Supports two patterns:

1. Inbox: producer stores, consumer polls or long-polls for message
2. Link: producer stores, waits for ACK; consumer fetches and ACKs

Memory is bounded by repository’s max_entries and per-entry waiter limits.

Implementations

impl WaitingList

pub fn new(repository: EntryRepository) -> Self

Creates a WaitingList with the given repository.

pub fn store( &mut self, id: String, message: Message, ttl: Duration, ) -> Result<()>

Stores a message, immediately notifying any long-polling subscribers.

On overwrite: message_waiters receive the new message; stale ack_waiters (from previous message) are dropped (their receivers get RecvError).

Returns an error if persistence fails. Waiters are notified regardless of persistence success (message is delivered but may not survive restart).

pub fn ack(&mut self, id: &str) -> bool

Marks entry as acknowledged, clearing message payload and notifying waiters.

Returns false if entry missing or expired (caller should return 404).

pub fn is_acked(&self, id: &str) -> Option<bool>

Returns whether an entry has been acknowledged.

Returns None if entry doesn’t exist or is expired, Some(bool) otherwise.

pub fn subscribe_ack( &mut self, id: &str, ) -> Result<Receiver<()>, SubscribeError>

Subscribes to receive notification when this entry is ACKed.

Returns Err(SubscribeError::NotFound) if entry missing/expired, Err(SubscribeError::WaiterLimitReached) if waiter limit reached.

pub fn get_or_subscribe( &mut self, id: &str, ) -> Result<GetOrSubscribeResult, SubscribeError>

Atomically checks for message and subscribes if not present.

Prevents TOCTOU race: without this, a separate “check then subscribe” would miss messages arriving between the two operations.

Creates a waiter entry if no message exists, allowing waiters to register before any message is stored (consumer arrives before producer).

pub fn cleanup_expired(&mut self) -> usize

Removes expired entries and cleans up stale waiters.