#5365: Finalizer running prematurely in ghci
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Reporter: ekmett | Owner: simonmar
Type: bug | Status: closed
Priority: normal | Milestone:
Component: GHCi | Version: 7.0.3
Resolution: invalid | Keywords: finalizers
Testcase: | Blockedby:
Difficulty: | Os: Unknown/Multiple
Blocking: | Architecture: Unknown/Multiple
Failure: Incorrect result at runtime |
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Changes (by simonmar):
* status: new => closed
* resolution: => invalid
Comment:
You are attaching a finalizer to `y`, which is a thunk. After `y` is
evaluated, the thunk is no longer referenced, so the finalizer runs. (`y`
might not look like a thunk, but it is in fact a call to
`unpackCString#`).
Usually you want to `seq` before calling `addFinalizer` for this reason,
although note that `seq` doesn't guarantee ordering so you could still get
unexpected results. This is probably better:
{{{
let y = "foo" in (unsafePerformIO $ do
y' <- evaluate y
addFinalizer y' (putStrLn $ "deleted")) `seq` y
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5365#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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