#4858: Add Control.Concurrent.forkIOWithUnmask, deprecate forkIOUnmasked
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Reporter: simonmar | Owner:
Type: proposal | Status: new
Priority: normal | Milestone:
Component: libraries/base | Version: 7.0.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Description changed by simonmar:
Old description:
> We added `forkIOUnmasked` as part of the new asynchronous exceptions API
> in base 4.3.0.0 (GHC 7.0.1). Unfortunately, `forkIOUnmasked` isn't very
> useful: the computation in the child thread is executed in the unmasked
> state, so the child doesn't have a way to reliably set up an exception
> handler before an asynchronous exception is raised.
>
> This proposal is to replace `forkIOUnmasked` with `forkIOWithUnmask`:
>
> {{{
> -- | Like 'forkIO', but the child thread is passed a function that can
> -- be used to unmask asynchronous exceptions. This function is
> -- typically used in the following way
> --
> -- > ... mask_ $ forkIOWithUnmask $ \unmask ->
> -- > catch (unmask ...) handler
> --
> -- so that the exception handler in the child thread is established
> -- with asynchronous exceptions masked, meanwhile the main body of
> -- the child thread is executed in the unmasked state.
> --
> -- Note that the unmask function passed to the child thread should
> -- only be used in that thread; the behaviour is undefined if it is
> -- invoked in a different thread.
> --
> forkIOWithUnmask :: ((forall a . IO a -> IO a) -> IO ()) -> IO ThreadId
> forkIOWithUnmask io = forkIO (io unsafeUnmask)
> }}}
>
> `forkIOUnmasked` will be deprecated.
>
> Some discussion leading up to this can be found in #3837.
New description:
We added `forkIOUnmasked` as part of the new asynchronous exceptions API
in base 4.3.0.0 (GHC 7.0.1). Unfortunately, `forkIOUnmasked` isn't very
useful: the computation in the child thread is executed in the unmasked
state, so the child doesn't have a way to reliably set up an exception
handler before an asynchronous exception is raised.
This proposal is to replace `forkIOUnmasked` with `forkIOWithUnmask`:
{{{
-- | Like 'forkIO', but the child thread is passed a function that can
-- be used to unmask asynchronous exceptions. This function is
-- typically used in the following way
--
-- > ... mask_ $ forkIOWithUnmask $ \unmask ->
-- > catch (unmask ...) handler
--
-- so that the exception handler in the child thread is established
-- with asynchronous exceptions masked, meanwhile the main body of
-- the child thread is executed in the unmasked state.
--
-- Note that the unmask function passed to the child thread should
-- only be used in that thread; the behaviour is undefined if it is
-- invoked in a different thread.
--
forkIOWithUnmask :: ((forall a . IO a -> IO a) -> IO ()) -> IO ThreadId
forkIOWithUnmask io = forkIO (io unsafeUnmask)
}}}
`forkIOUnmasked` will be deprecated.
Some discussion leading up to this can be found in #3837.
Discussion period: 3 weeks (until 12 Jan 2011)
--
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4858#comment:1>
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