Opening and closing a hslogger log file, within the GHCi REPL

Question

I am annoyed with my implementation of hslogger, when running within the GHCi REPL.

import System.IO (Handle)
import System.Log.Logger (Priority( DEBUG ), updateGlobalLogger, addHandler, setLevel, debugM)
import System.Log.Handler.Simple (fileHandler)
import System.Log.Handler (setFormatter, close)

main :: IO ()
main = do
    f <- fileHandler "sample.log" DEBUG
    updateGlobalLogger "Component" (addHandler f)
    updateGlobalLogger "Component" (setLevel DEBUG)
    debugM "Component" "This is a sample log line"
    close f

It runs without exception the first time, however, on subsequent executions of main:

*** Exception: sample.log: hPutStr: illegal operation (handle is closed)

This is not experienced when I'm running the program outside of GHCi.

Am I not closing the file handle correctly with hslogger, or does GHCi keep the file handle open?

I don't the experience the same problem when opening and closing a standard file.

import System.IO (Handle, openFile, hClose, hPutStrLn, IOMode (WriteMode))

main :: IO ()
main = do
    f <- openFile "sampleFile.log" WriteMode
    hPutStrLn f "Hello"
    hClose f

score 1 · Accepted Answer · answered Mar 05 '15 at 22:09

Using removeHandler in conjunction with close seems to work:

import System.IO (Handle)
import System.Log.Logger (Priority( DEBUG ), updateGlobalLogger, addHandler, setLevel, debugM, removeHandler)
import System.Log.Handler.Simple (fileHandler)
import System.Log.Handler (setFormatter, close)

main1 :: FilePath -> IO ()
main1 fp = do
    f <- fileHandler fp DEBUG
    updateGlobalLogger "Component" (addHandler f)
    updateGlobalLogger "Component" (setLevel DEBUG)
    debugM "Component" ("This is a sample log line to file " ++ fp)
    updateGlobalLogger "Component" removeHandler
    close f

main = do main1 "foo.log"; main1 "foo.log"

Great. Now to properly clean up when exceptions arise. – indi Mar 06 '15 at 10:30 — indi, Mar 06 '15 at 10:30

Opening and closing a hslogger log file, within the GHCi REPL

1 Answers1