Question

I’m creating a Happstack server application, but I don’t know how to end the application .

If I have:

main = do
  printf "begin server"
  simpleHTTP nullConf myHomepage
  printf "end server"

I can run it ok, and I can kill the application (linux) with CTRL+C, but the last print is never executed. How can I exit gracefully from Happstack? It bothers me because I notice that eventlog is not generated if I don’t exit correctly from the application.

UPDATE:

The application is using Dyre at the top main.

Answer 1

I generally use forkIO to spawn simpleHTTP in a separate thread. And then waitForTermination to wait for ^C.

module Main where

import Control.Concurrent (killThread, forkIO)
import Happstack.Server (nullConf, simpleHTTP, ok, toResponse)
import Happstack.State (waitForTermination)

main :: IO ()
main =
    do putStrLn "begin server"
       httpThreadId <- forkIO $ simpleHTTP nullConf (ok $ toResponse "This site rules!")
       waitForTermination
       killThread httpThreadId
       putStrLn "end server"

waitForTermination comes from the happstack-state package. It really needs to be moved somewhere else for multiple reasons. If you don’t want to install happstack-state you can copy and paste a local copy into your app:

-- | Wait for a signal.
--   On unix, a signal is sigINT or sigTERM. 
waitForTermination :: IO ()
waitForTermination
    = do istty <- queryTerminal stdInput
         mv <- newEmptyMVar
         installHandler softwareTermination (CatchOnce (putMVar mv ())) Nothing
         case istty of
           True  -> do installHandler keyboardSignal (CatchOnce (putMVar mv ())) Nothing
                       return ()
           False -> return ()
         takeMVar mv