Deadlock in the threaded RTS
The following program deadlocks with high probability:
-- ghc -rtsopts -threaded -debug performGC.hs
-- ./performGC 1000 +RTS -qg -N2
-- -qg turns off parallel GC, needed to trigger the bug
-- -N2 or greater is needed
module Main (main) where
import System.Environment
import Control.Concurrent
import Control.Exception
import Control.Monad
import System.Random
import System.Mem
import qualified Data.Set as Set
main = do
[n] <- getArgs
forkIO $ doSomeWork
forM [1..read n] $ \n -> do print n; threadDelay 1000; performMinorGC
doSomeWork :: IO ()
doSomeWork = forever $ do
ns <- replicateM 10000 randomIO :: IO [Int]
ms <- replicateM 1000 randomIO
let set = Set.fromList ns
elems = filter (`Set.member` set) ms
evaluate $ sum elemsThere are a few ways that this bug can be triggered:
- At shutdown, when there are other threads still running. This is how we first encountered it.
- Using
performGC, as above. I think it's necessary to call it from a bound thread (e.g. the main thread) to get bad things to happen. - I think
forkProcessmight also trigger it, but I haven't observed it.
I'm working on a fix.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.10.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | highest |
| Resolution | Unresolved |
| Component | Runtime System |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | niteria, simonmar |
| Operating system | |
| Architecture |
