#8006: Asynchronous exception rethrown synchronously inside runStmt ---------------------------------+------------------------------------------ Reporter: edsko | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------ Comment(by simonmar): If repeating the I/O is what you want, then you can do that - indeed, that's what I suggested that we should do, and this ticket is Edsko's followup after investigating that possibility. For some background, we adopted this approach in the I/O library for lazy I/O, see #3997, and `Note [async]` in `libraries/base/GHC/IO/Handle/Internals.hs`. Edsko's objection to doing this in GHC is that there are a lot of places where we catch exceptions inside `unsafePerformIO` or equivalent, and it probably isn't safe to repeat the I/O in all of them. Well, maybe it is - I'm not sure. The semantics of async exceptions doesn't say anything about this, because it doesn't include `unsafePerformIO` - IO is strictly at a higher level than pure computation. What seems attractive about having a different kind of catch is that it avoids the problem in cases where we're only interested in catching a subset of exceptions, which is what we're doing in GHC: both `tryM` and `tryMostM` want to just pass through async exceptions. You're right that it doesn't help if you want to do some cleanup (`bracket` or `finally`). -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/8006#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler