[Haskell-cafe] Ctrl-C handling in Haskell with curl on Linux
vasyl.pasternak at gmail.com
Thu Sep 24 05:30:46 EDT 2009
Yesterday I tried to implement simple tool to download pages, and wanted
catch Ctrl-C (and other 'killing' messages) from haskell to handle state
saving. Without curl (when I perform some long operation) haskell throws
UserInterrupt exception immediately, but if I put long operation, which
downloads page from the WEB (from the far-far-away server :) ) than I
noticed following issues:
- to break my program I have to press Ctrl-C twice
- haskell doesn't throw an exception
- when I rewrite this code to use signals, haskell, after I press Ctrl-C
several times exits with error "too many pending signals"
I put the test code in the end of the letter. Shortly the longTask doesn't
handle Ctrl-C and longTask' handles it.
I couldn't find any solutions to this problem, I am afraid that this problem
could occur in other non-native haskell modules (bindings to C libraries)
Many thanks in advance,
module Main where
import Prelude hiding (catch)
errorHandler defVal e = do
putStrLn $ "Error: " ++ (show (e :: ErrorCall))
link = "far-far-away-site.com.net"
getSite curl l = do
r <- do_curl_ curl l method_GET :: IO (CurlResponse)
if respCurlCode r /= CurlOK
then error "get page failed"
else return $ respBody r
-- this long task doesn't throw user interrupts
longTask = do
putStrLn "Long task started"
curl <- initialize
setopts curl [CurlCookieJar "cookies"]
handle (errorHandler ()) $
mapM_ (\_ -> getSite curl link >> return ()) [0..100]
-- this trows
longTask' = do
putStrLn "long task started"
let fib n = foldr (*) 1 [1..n]
h <- openFile "/dev/null" WriteMode
-- never ends
mapM_ (hPutStr h . show . fib) [1..]
onAbort e = do
let x = show (e :: AsyncException)
putStrLn $ "Aborted: " ++ x
main :: IO ()
main = do
handle onAbort longTask
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