The only progress I made was to start this thread on the ghc-users
mailing list:
http://www.haskell.org/pipermail/glasgow-haskell-users/2014-July/025107.html
The #1 issue I have is that it's not clear what changed in the
transition from ghc-7.6 to ghc-7.8 that caused this problem. I think if
we understood that we can better understand the potential solutions.
The worst case scenario (if the problem is can't be resolved) is that I
just change the type of `spawn` to:
spawn :: Buffer a -> Managed (Output a, Input a, STM ())
... where that will automatically `seal` the action when done. It's not
as useful, but at least it will avoid the exception.
On 8/16/14, 2:14 PM, Tony Day wrote:
Any progress on this Gabe?
I was thinking of diving in and exploring weak references if no
immediate solution has presented itself.
Knowing absolutely zero about them, to what extent could I apply
equational reasoning to the minimum code, given the effects in there?
I took the liberty of adding this as an open issue on github.
On Monday, July 14, 2014 5:04:48 AM UTC+10, Gabriel Gonzalez wrote:
Alright, so even when I switched to the safe `mkWeakTVar` I still
see the exact same issue. I've also reduced the minimal
reproducing program to:
import Pipes.Concurrent
main = do
(_, input) <- spawn Unbounded
atomically $ recv input
It seems like something has fundamentally changed about how weak
references interact with STM transactions in ghc-7.8. Right now I
am trying to see if there is some other way to accomplish the same
behavior without weak references.
On 7/7/14, 3:53 PM, Michael Thompson wrote:
The bit about user input was nonsense; the example wasn't using
the `user` it defined. Here is a more minimal main (with the
same `worker`):
main = do
(output, input) <- spawn (Bounded 1)
a1 <- async $ runEffect $ fromInput input >-> worker 1
a2 <- async $ runEffect $ yield 1 >-> toOutput output
wait a1
wait a2
$ ./work
Worker #1: Processed 1
work: thread blocked indefinitely in an STM transaction
It works if a higher `Bounded` or if `Unbounded` is chosen; it
works if the second `wait` is dropped, etc.
The most striking difference was the use of `Unbounded` in the
good version and `Bounded` in the separate module.
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