If you want to guarantee safety, you can use an MVar () to force
serialization; put something in the MVar inside of catchDyn, and take
from it immediately after starting the thread & after throwing each
exception.
-- ryan
On Feb 10, 2008 11:49 AM, Thomas DuBuisson <[EMAIL PROTECTED]> wrote:
> Cafe,
> Fact 1: ghc{,i} does not crash when executing this code.
> Fact 2: I do not want this to crash.
> Question: Is there some theoretical window between the 'catchDyn' exception
> handling and the recursive call to 'catchThatDamnError' that could result in
> an unhandled exception? (of type 'DynError', of coarse)
>
> I suppose I am looking for an answer to this question from a language
> standpoint as well as a compiler pov.
>
> As an aside: I see at least one way to be certain of the safty by wrapping
> the call to forkIO in 'catchDyn', reforking if an exception is caught, and
> passing the new ThreadId to throwConstantly via shared mutable state - I'd
> like to avoid all this if my current example is safe.
>
> Thomas
>
> > import Control.Exception (catchDyn, throwDynTo)
> > import Control.Concurrent (forkIO, threadDelay)
> > import Control.Monad (forever)
> > import Data.Dynamic
> >
> > main = do
> > tid <- forkIO catchThatDamnError
> > forever $ throwConstantly tid
> >
> > catchThatDamnError = catchDyn start (\DynError -> catchThatDamnError)
> >
> > start = do
> > threadDelay 5000
> > start
> >
> > throwConstantly tid = do
> > throwDynTo tid DynError
> >
> > data DynError = DynError deriving (Eq, Ord, Show, Typeable)
>
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