Graceful Shutdown

Install signal handlers after the worker configurations exist. Pass the same pool list to shutdownWorkerPools and runWorkerPools:

import System.Posix.Signals qualified as Signals

emailConfig <- Worker.transactionalWorkerConfig 3 processEmail
imageConfig <- Worker.transactionalWorkerConfig 2 processImage

let workers = [Worker.namedWorkerPool emailConfig, Worker.namedWorkerPool imageConfig]
    shutdown = Signals.Catch $ Worker.shutdownWorkerPools workers
void $ Signals.installHandler Signals.sigTERM shutdown Nothing
void $ Signals.installHandler Signals.sigINT shutdown Nothing

poolCfg <- Worker.poolConfigForWorkers workers
env <- ArbS.createSimpleEnvWithConfig (Proxy @AppRegistry) connStr "arbiter" poolCfg
ArbS.runSimpleDb env $ Worker.runWorkerPools workers

The dispatcher stops claiming and waits for in-flight jobs. runWorkerPools returns when they finish or after gracefulShutdownTimeout. A job still running at the timeout is left unfinalized and redelivered after its lease expires.