getChanContents exception behavior seems a bit odd
I've been playing around with Control.Concurrent.Chan today. Something seems a bit off:
-- Bug.hs
import Control.Concurrent (forkIO, yield)
import Control.Concurrent.Chan
import Data.List (elem)
import Control.Exception
import Control.Concurrent.MVar
data Ex = Ex deriving Show
instance Exception Ex
main = do
ch <- newChan
sync1 <- newEmptyMVar
sync2 <- newEmptyMVar
forkIO $ do {writeList2Chan ch [1..3*10^6 :: Int]; putMVar sync1 ()}
yield
writeChan ch (-12)
cont <- getChanContents ch
tid <- forkIO $ do
evaluate (last cont)
putMVar sync2 ()
yield
throwTo tid Ex
print (elem (3*10^6) cont)
takeMVar sync1
tryTakeMVar sync2When I run this single-threaded (+RTS -N1), it prints
Bug: Ex
Bug: ExOne of the thunks in the lazy list gets overwritten by the (asynchronous) exception. This seems a bit surprising; is it the way it should be? Does hGetContents do this too?
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.4.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Core Libraries |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | simonmar |
| Operating system | |
| Architecture |