supervise

This library facilitates the spawning, maintenance and resolution of asynchronous operations running concurrently. See example below for more info:

module Main where

import Concurrency.Supervise ( supervise, ThreadCount(..), RespawnTime(..), Supervise(..), poll )
import Control.Concurrent
import Control.Exception
import Control.Monad
import System.Exit
import System.Random

secs :: Int -> Int
secs = (*1000000)

main :: IO ()
main = do
  Supervise
    threadcount -- MVar to change the current amount of running threads
    respawnTime -- MVar to change the respawn time of asynchronous actions
    adminThread -- Admin thread for monitoring
        <-
      supervise -- * Main API function we care about
        (ThreadCount 5)   -- This means 5 threads will run 'action' concurrently
        (RespawnTime 0)   -- Time elapsed before the next thread respawns
        action            -- IO action to run
        handleExceptions  -- Exception handler
        handleCompletions -- Completion handler

  -- Monitor the admin thread
  forever $ do
    res <- poll adminThread
    case res of
      Nothing        -> putStrLn "adming running..."
      Just (Right x) -> putStrLn "admin completed.."
      Just (Left x)  -> putStrLn "admin error.."
    threadDelay (secs 2)

  -- Example
  where handleExceptions    = print
        handleCompletions x = print "finished action.."
        action              = do r <- randomRIO (1,10)
                                 threadDelay (secs r)
                                 putStrLn $ "running action..." ++ show r ++ " secs"