#2401: unsafeIOToSTM hangs with 64 bit multicore.
----------------------------+-----------------------------------------------
Reporter: sclv | Owner:
Type: bug | Status: closed
Priority: normal | Milestone: 6.10.1
Component: Runtime System | Version: 6.8.3
Severity: major | Resolution: wontfix
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Changes (by simonmar):
* status: new => closed
* resolution: => wontfix
Comment:
I understand what's happening here. Inside a transaction you're doing
this:
{{{
unsafeIOToSTM $ putStrLn ".."
}}}
Now, `putStrLn` needs to take a lock on `stdin`. But the STM
implementation assumes it can abort a transaction at any time, and in this
case it aborts a transaction in the middle of `putStrLn` (because it
discovered the transaction was already invalid). When it aborts the
transaction, the exception handler in `putStrLn` is discarded (STM didn't
expect there to be a real IO exception handler in the middle of a
transaction). So `stdin` remains locked, and the program eventually
deadlocks.
Perhaps we could fix this by throwing a real exception, but there's quite
a large design space there, and in any case when using `unsafeIOToSTM`
you're really on your own. I'll put a big warning in the docs for
`unsafeIOToSTM` though.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2401#comment:4>
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