Guard.hs

-- Communicating Haskell Processes.
-- Copyright (c) 2008, University of Kent.
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module Control.Concurrent.CHP.Guard where

import Control.Concurrent.STM
import Control.Monad.Trans
import Data.Unique
import System.IO

import Control.Concurrent.CHP.Event
import Control.Concurrent.CHP.Traces.Base

-- Setup (giving transaction)
data Guard = TimeoutGuard (IO (STM ()))
             | SkipGuard
             | StopGuard
             -- The STM item is an action to take in the same transaction as
             -- completing the event (before it is completed).
             | EventGuard ((Unique -> Integer) -> [RecordedIndivEvent Unique]) (STM ()) [Event]

skipGuard :: Guard
skipGuard = SkipGuard

isSkipGuard :: Guard -> Bool
isSkipGuard SkipGuard = True
isSkipGuard _ = False

badGuard :: String -> Either String a
badGuard = Left

stopGuard :: Guard
stopGuard = StopGuard

isStopGuard :: Guard -> Bool
isStopGuard StopGuard = True
isStopGuard _ = False

-- Microseconds
guardWaitFor :: Int -> Guard
guardWaitFor n
  = TimeoutGuard $ 
     do signalDone <- liftIO $ registerDelay n
        return $ do b <- readTVar signalDone
                    if b == False
                      then retry
                      else return ()