RE: signal handling and optimisation

23 Jun 2003

...
I'm trying to write some code that catches unix signals and turns them
into GHC exceptions, GHC version 6.0, debian linux
Heres my code:
------
   module Main where
import Control.Concurrent
   import Control.Exception
   import System.Posix
   import IO
catchCtrlC :: IO Handler
   catchCtrlC
      = do main_thread <- myThreadId
           installHandler sigINT (Catch (handler main_thread)) Nothing
           where
           handler :: ThreadId -> IO ()
           handler main_thread = throwTo main_thread 
(ErrorCall "Kaboom")
main :: IO ()
   main = do catchCtrlC 
             print (f 1)
f :: Int -> Int
   f x = f (x + 1)
------
The function "f" is intentionally bogus, I want it to loop so 
I have enough time to hit cntrl-C.
You've hit a known bug with concurrency, described in the
Control.Concurrent documentation.

The problem is that context switches only happen when some allocation is
going on: in your f function above, the optimiser turns it into a loop
that does no allocation, so no context switches can happen and the
exception is never delivered.

You probably won't run into this bug in a real program ;-)

Cheers,
	Simon

RE: signal handling and optimisation

Simon Marlow