[Haskell-cafe] ANN: asynchronous-exceptions

[Roman Cheplyaka]

Hi João,

* João Cristóvão <jmacristovao at gmail.com> [2014-02-05 15:53:34+0000]
> Hi Roman,
> 
> One other question: in Michael's article, he also mentions the possibility of:
> "Consider that, for some strange reason, we decided to asynchronously
> throw an IOException to a worker thread"
> 
> Meaning that you can throwTo any exception asynchronouly, even if it
> is not a SomeAsyncException. At least from what I gathered from (GHC
> Head) throwTo code, this does not seem to be a restriction.
> 
> Thus, your module will work for any well behaved code that does the
> right thing, and respects the SomeAsyncException superclass, but not
> for other spurious asynchronous exceptions, right?

Precisely.

> I'm just trying to frame the possible use cases of your library.
> Thanks
> Joao
> 
> 2014-02-05 Roman Cheplyaka <roma at ro-che.info>:
> > 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
> >> >
> >> >
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe at haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: Digital signature
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140205/3f9c4f66/attachment.sig>