Starts a worker pool with a dispatcher and N worker threads.

A worker pool bundled with its queue name from the type-level registry.

The queue name is derived from the registry at compile time, ensuring it stays in sync with the type-level definition.

Use namedWorkerPool to construct these, then runSelectedWorkerPools to run only the ones matching a runtime configuration.

Example:

allWorkers :: [NamedWorkerPool (SimpleDb MyRegistry IO)]
allWorkers =
  [ namedWorkerPool emailConfig      -- name derived from registry: "email_jobs"
  , namedWorkerPool imageConfig      -- name derived from registry: "image_jobs"
  , namedWorkerPool notifConfig      -- name derived from registry: "notifications"
  ]

main = runWorkerPools (Proxy @MyRegistry) allWorkers (\_ -> pure ())

Create a named worker pool, deriving the name from the type-level registry.

Run worker pools with shared state for coordinated shutdown.

Creates shared state, passes it to setup action (for signal handlers), then runs pools. Reads enabled queues from ARBITER_ENABLED_QUEUES.

Run only the worker pools whose names appear in the enabled list.

Get enabled queues from an environment variable.

If the environment variable is set and non-empty, parses it as a comma-separated list of queue names. Each name is validated against the registry - invalid names cause an error. If not set or empty, returns all queue names from the registry.

Example:

-- With ENABLED_QUEUES="email_jobs,notifications"
queues <- getEnabledQueues ENABLED_QUEUES (Proxy @MyRegistry)
-- Returns: ["email_jobs", "notifications"]

-- With ENABLED_QUEUES unset or empty
queues <- getEnabledQueues ENABLED_QUEUES (Proxy @MyRegistry)
-- Returns: all queues from registry

-- With ENABLED_QUEUES="email_jobs,invalid_queue"
-- Throws error: "Unknown queue names: invalid_queue"

Handler result types. () is fire-and-forget; any (ToJSON a, FromJSON a) is stored in the results table when the job has a parent and decoded when read by a rollup finalizer.

A cron schedule definition.

Use cronJob to construct — it parses the cron expression eagerly, so invalid expressions are caught at construction time.

Determines how overlapping cron ticks are deduplicated.

Smart constructor for CronJob. Parses the cron expression eagerly.

Returns Left with an error message if the cron expression is invalid.

Note: cron expressions are evaluated in UTC. "0 3 * * *" fires at 03:00 UTC regardless of the server's local timezone.

Example:

cronJob "nightly-report" "0 3 * * *" SkipOverlap
  (\_ -> defaultJob (GenerateReport "nightly"))

Initialize the cron_schedules table and upsert defaults for all cron jobs.

Called once at scheduler startup. Upserts default_expression and default_overlap for each CronJob, preserving any user overrides and enabled state.

Convert an OverlapPolicy to its text representation.

Parse an OverlapPolicy from text.