Struct Listener 

pub struct Listener { /* private fields */ }

Processes events from the event bus.

Listens for events, handles them with registered handlers, and manages retry logic with exponential backoff.

Implementations

impl Listener

pub fn new(pool: PgPool, registry: EventHandlerRegistry) -> Self

Creates a new listener with default configuration.

Default settings: 3 max attempts, 15 second base retry duration.

Arguments

• pool - Database connection pool
• registry - Registry containing event handlers

pub fn with_max_attempts(self, max_attempts: u16) -> Self

Sets maximum retry attempts before moving events to dead letter queue.

Arguments

• max_attempts - Maximum number of processing attempts (1-65535)

pub fn with_retry_duration(self, retry_duration: Duration) -> Self

Sets base duration for exponential backoff retry delays.

Actual delay = base_duration * 2^(attempt - 1)

Arguments

• retry_duration - Base duration for retry calculations

impl Listener

pub async fn listen(&mut self, tx: Option<Sender<Handled>>) -> Result<(), Error>

Starts the event listener loop.

Continuously polls for events using PostgreSQL LISTEN/NOTIFY with intelligent backoff. Processes events until the loop is stopped.

Arguments

• tx - Optional channel to send polling results to

Errors

Returns database errors if connection or polling fails.

impl Listener

pub async fn poll(&self, now: DateTime<Utc>) -> Result<Option<Uuid>, Error>

Polls for and processes a single event.

Prioritizes unacknowledged events over retry events. Handles the event with registered handlers and manages success/failure reporting.

Arguments

• now - Current timestamp for processing

Returns

Returns the UUID of the processed event, or None if no events were available.

Errors

Returns database errors if polling or transaction operations fail.

impl Listener

pub async fn poll_retryable<'tx>( tx: &mut PgTransaction<'tx>, now: DateTime<Utc>, ) -> Result<Option<RawEvent>, Error>

Polls for retryable events that are ready for another processing attempt.

Uses FOR UPDATE SKIP LOCKED to atomically claim retryable events while maintaining FIFO ordering and avoiding contention between concurrent listeners.

Arguments

• tx - Database transaction to use for the operation
• now - Current timestamp to check against retry deadlines

Returns

Returns the next retryable event if one is available and ready, or None if no events are ready for retry.

Errors

Returns database errors if the query or transaction operations fail.