[Haskell-cafe] ANN: asynchronous-exceptions

[Roman Cheplyaka]

It works as expected.

With GHC 7.8 it doesn't print the timeout exception.

With earlier GHC it does (again, as expected, because the timeout
exception isn't marked as asynchronous). In practice one should rarely
want to use System.Timeout anyway (because of the overflow issue), and
I'm going to patch one of the better timeout packages (such as
unbounded-delays) to support asynchronous-exceptions.

* Michael Snoyman <michael at snoyman.com> [2014-02-05 16:56:31+0200]
> I don't think this package works as expected. Consider the following:
> 
> import           Control.Concurrent
> import           Control.Exception.Async
> import           System.Timeout
> 
> main :: IO ()
> main = do
>     timeout 1000000 $ do
>         threadDelay 10000000 `catchSync` \e -> do
>             print e
>             threadDelay 10000000
>     return ()
> 
> The expected behavior would be that the timeout- an async exception- would
> kill the thread delay, the catch would ignore the async exception, and the
> program would exit. In reality, catchSync treats the timeout as a
> synchronous exception, prints it, and delays once again. Compare this to
> classy-prelude's catchAny, which handles the situation correctly, via the
> technique I described in "Catching all exceptions."[1]
> 
> In this case, the issue is that the timeout exception type is not
> recognized as async, and a special case could be added to handle that
> exception type[2]. However, I think the overall approach of determining
> *how* an exception was thrown based on *what* was thrown is not tenable.
> 
> [1]
> https://www.fpcomplete.com/user/snoyberg/general-haskell/exceptions/catching-all-exceptions
> [2] It's a bit difficult to do so, since IIRC the type is never exported.
> But a hack using the Typeable instance- while ugly- is likely possible.
> 
> 
> On Wed, Feb 5, 2014 at 1:28 PM, Roman Cheplyaka <roma at ro-che.info> wrote:
> 
> > The links are:
> >
> > http://hackage.haskell.org/package/asynchronous-exceptions
> > https://github.com/feuerbach/asynchronous-exceptions
> >
> > * Roman Cheplyaka <roma at ro-che.info> [2014-02-05 13:23:38+0200]
> > > It is often useful to distinguish between synchronous and asynchronous
> > > exceptions. The common idiom is to run a user-supplied computation
> > > catching any synchronous exceptions but allowing asynchronous exceptions
> > > (such as user interrupt) pass through.
> > >
> > > base 4.7 (shipped with GHC 7.8) will have SomeAsyncException type that
> > > solves this problem.
> > >
> > > asynchronous-exceptions is a new package that serves two purposes:
> > > * provide compatibility with older `base` versions that lack the
> > >   `SomeAsyncException` type
> > > * define convenient functions for catching only synchronous exceptions
> > >
> > > Roman
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe at haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
> >
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