#4162: GHC API messes up signal handlers
---------------------------------+------------------------------------------
Reporter: jcpetruzza | Owner:
Type: bug | Status: new
Priority: normal | Component: GHC API
Version: 6.12.3 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
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A side-effect of using the {{{runGhc}}} function is that some signal
handlers are modified and not restored afterwards (see function
{{{initGhcMonad}}}). In particular, the handler for {{{SIGINT}}} installed
by ghc throws an exception to a thread stored in a global variable, which
initially corresponds to the thread from which {{{runGhc}}} was run.
This is a particularly problematic for programs that wish to run ghc "in
the background" on its own thread. For example, consider this code:
{{{
import qualified GHC
import qualified MonadUtils as GHC
import qualified GHC.Paths as GHC
import Control.Concurrent ( forkIO, threadDelay )
main = do
putStrLn "waiting for 5 seconds..."
threadDelay $ 5 * 1000 * 1000
putStrLn "starting..."
forkIO $ GHC.runGhc (Just GHC.libdir) (GHC.liftIO $ putStrLn "hello")
putStrLn "waiting for 10 seconds"
threadDelay $ 10 * 1000 * 1000
putStrLn "exiting after final wait"
}}}
One can interrupt this program with Ctrl-C during the first five seconds
of execution only.
It is not clear to me how one can safely workaround this problem. For
instance, one could manually restore the program's original handlers at
the beginning of execution, that is, transform:
{{{
runGhc action
}}}
into something like this:
{{{
runGhc $ (liftIO restoreProgramHandlers >> action)
}}}
but I don't know if this is safe (i.e., what happens if ghc is run without
its own handlers installed).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4162>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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