[Haskell-cafe] Ctrl-C handling in Haskell with curl on Linux

Vasyl Pasternak vasyl.pasternak at gmail.com
Thu Sep 24 08:24:16 EDT 2009

Thank you,

You give me and idea, and I fixed this annoying bug - we should only wrap
curl code into withCurlDo function, so the longTask function should be

longTask = do
  putStrLn "Long task started (curl)"
  withCurlDo $ do
             curl <- initialize
             setopts curl [CurlCookieJar "cookies"]

             handle (errorHandler ()) $
                    mapM_ (\_ -> getSite curl link >> return ()) [0..100]
  return ()

Now it works fine and handles interrupts correctly.

Best regards,
Vasyl Pasternak

2009/9/24 Brandon S. Allbery KF8NH <allbery at ece.cmu.edu>

> On Sep 24, 2009, at 06:20 , Brandon S. Allbery KF8NH wrote:
> On Sep 24, 2009, at 05:30 , Vasyl Pasternak wrote:
> 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:
> You're going to have problems any time a C library installs its own signal
> handler, which I would expect libcurl to do so it can clean up after itself.
>  This is true even in C-to-C calling; you need a way to hook the signal
> handler, which some libraries provide in their API and others you just lose.
> Just occurred to me I should clarify:  while most exception handling
> mechanisms support the concept of re-throwing exceptions to outer exception
> handlers, POSIX signals do not.  The best you could hope for in a library
> routine which handles signals itself is an API hook into the signal handler;
> next best is the API returning a signal-occurred error/exception value.
> Note that I have no idea how the equivalent signaling mechanism works on
> Win32.
> --
> brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
> system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
> electrical and computer engineering, carnegie mellon university    KF8NH
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