Monitor.hs

{-# options_haddock prune #-}
-- |Description: Monitor Interpreters, Internal
module Polysemy.Conc.Interpreter.Monitor where

import qualified Control.Exception as Base
import Polysemy (embedFinal, runTSimple)
import Polysemy.Async (Async)
import Polysemy.Error (errorToIOFinal, fromExceptionSem)
import Polysemy.Resource (Resource)
import qualified Polysemy.Time as Time
import Polysemy.Time (Time)

import Polysemy.Conc.Async (withAsync_)
import Polysemy.Conc.Effect.Monitor (
  Monitor (Monitor),
  MonitorCheck (MonitorCheck),
  MonitorResource (MonitorResource),
  RestartingMonitor,
  ScopedMonitor,
  )
import qualified Polysemy.Conc.Effect.Race as Race
import Polysemy.Conc.Effect.Race (Race)
import Polysemy.Conc.Interpreter.Scoped (runScoped, runScopedAs)

newtype CancelResource =
  CancelResource { signal :: MVar () }

data MonitorCancel =
  MonitorCancel
  deriving (Eq, Show, Exception)

interpretMonitorCancel ::
  Members [Race, Async, Final IO] r =>
  MonitorResource CancelResource ->
  InterpreterFor (Monitor action) r
interpretMonitorCancel (MonitorResource CancelResource {..}) =
  interpretH \case
    Monitor ma ->
      leftM (Base.throw MonitorCancel) =<< Race.race (embedFinal @IO (readMVar signal)) (runTSimple ma)

monitorRestart ::
  ∀ t d r a .
  Members [Time t d, Resource, Async, Race, Final IO] r =>
  MonitorCheck r ->
  (MonitorResource CancelResource -> Sem r a) ->
  Sem r a
monitorRestart (MonitorCheck interval check) run = do
  sig <- embedFinal @IO newEmptyMVar
  withAsync_ (Time.loop_ @t @d interval (check sig)) (spin sig)
  where
    spin sig = do
      let res = (MonitorResource (CancelResource sig))
      void (embedFinal @IO (tryTakeMVar sig))
      leftM (spin sig) =<< errorToIOFinal @MonitorCancel (fromExceptionSem @MonitorCancel (raise (run res)))

-- |Interpret @'Scoped' 'Monitor'@ with the 'Restart' strategy.
-- This takes a check action that may put an 'MVar' when the scoped region should be restarted.
-- The check is executed in a loop, with an interval given in 'MonitorCheck'.
interpretMonitorRestart ::
  ∀ t d r .
  Members [Time t d, Resource, Async, Race, Final IO] r =>
  MonitorCheck r ->
  InterpreterFor (RestartingMonitor CancelResource) r
interpretMonitorRestart check =
  runScoped (monitorRestart @t @d check) interpretMonitorCancel

interpretMonitorPure' :: MonitorResource () -> InterpreterFor (Monitor action) r
interpretMonitorPure' _ =
  interpretH \case
    Monitor ma ->
      runTSimple ma

-- |Run 'Monitor' as a no-op.
interpretMonitorPure :: InterpreterFor (ScopedMonitor () action) r
interpretMonitorPure =
  runScopedAs (pure (MonitorResource ())) interpretMonitorPure'