New post from Yuras provides food for thought:
https://github.com/Yuras/io-region/wiki/Handling-%28async%29-exceptions-in-h...
In particular he points out a case for which uninterruptibleMask will cause
unkillable threads: let's say hClose blocks flushing the output to a file,
but the write fails because of a hardware error and blocks forever.
(Alternatively, imagine the file is on NFS and you get a cable cut between
the two machines). The thread executing hClose in the cleanup action
becomes unkillable.
G
On Thu, Nov 20, 2014 at 7:24 AM, Simon Marlow
On 19/11/2014 23:07, Ganesh Sittampalam wrote:
On 13/11/2014 10:44, Simon Marlow wrote:
On 13/11/2014 07:47, Merijn Verstraaten wrote:
A new version would look like:
bracket before after thing = mask $ \restore -> do let atomicAfter = uninterruptibleMask . after a <- before r <- restore (thing a) `onException` atomicAfter a _ <- atomicAfter a return r
Slightly different versions are possible and the other relevant bracketing functions mentioned in this thread can be treated similarly.
Since we would need this for catch too, the sensible thing to do (if we decide to go ahead with this) would be to change the implementation of catch in the RTS from masking the exception handler to uninterruptibleMask. That would mean that at least for catch there would be no additional overhead, and it would make the modifications to the other operations simpler in some cases.
If this isn't done in the RTS, is there a possibility of an async exception slipping in between the exception handler starting and the uninterruptibleMask starting?
No, because the exception handler is masked.
Cheers, Simon
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Gregory Collins