On Wed, Apr 05, 2006 at 07:47:08AM -0400, David Roundy wrote:
For me, asynchronous exceptions are the primary reason to use concurrent Haskell. They're the only way I'm aware of to write a program that handles signals in Haskell, and it's be a real shame to leave Haskell' programs unable to handle signals--it means that any real-world programs that deal with locking or the like will need to use non-standard extensions. Unless you can come up with some other way to deal with signals. Having no chance to clean up when control-C is hit isn't an acceptable alternative, and neither is simply ignoring control-C and forcing users to run kill (and then once again get no chance to clean up!).
I have been giving signals some thought, and resarching what other languages do, and have a semi-proposal-maybe. signals tend to be used for one of a couple purposes (some can fall into multiple categories): signal a synchronous exceptional event - SIGFPE, SIGPIPE, SIGILL, SIGSEGV signal an asynchronous exceptional event - SIGINT, SIGHUP (interactive) inform the app of an event it might want to take note of - SIGALRM, SIGCHLD, SIGWINCH, SIGHUP (daemon) I think it would make sense to have 3 mechanisms to cover these cases. signal a synchronous exceptional event - raise a (possibly imprecise) exception on the thread that produced the signal. signal an asynchronous exceptional event - the user should be able to choose the threads on which they wish to catch these, those that need to clean up after themselves. inform the app of an event it might want to take note of - these should run on their own thread, concurrently to all other threads data Signal = ... data SigInfo = SigInfo { ... } -- | declare which signals should throw a synchronous exception always (because they are thread specific) signalException :: [Signal] -> IO () signalExceution = ... -- | declare that a thread should catch the given asynchronous signals during the processing of the argument signalCatch :: [Signal] -- ^ the signals I care about -> IO a -- ^ while running this, signals will be delivered as an exception to this one. (not necessarily exclusively) -> IO a signalCatch = ... -- | declare a signal should perform a task in its own thread, exceptions thrown will be discarded. signalAction :: [Signal] -> (SigInfo -> IO ()) -> IO () signalAction = ... these roughly corespond to the Core,Term,and Ign type signals respectivly. ideally, we should specify some default behaior, ILL,FPE,SEGV raise synchronous exceptions SIGPIPE ignored John -- John Meacham - ⑆repetae.net⑆john⑈