#7170: Foreign.Concurrent finalizer called twice in some cases
------------------------------+---------------------------------------------
Reporter: joeyadams | Owner:
Type: bug | Status: new
Priority: normal | Component: Runtime System
Version: 7.4.2 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: Runtime crash | Testcase:
Blockedby: | Blocking:
Related: |
------------------------------+---------------------------------------------
When [http://hackage.haskell.org/packages/archive/base/latest/doc/html
/Foreign-Concurrent.html#v:newForeignPtr Foreign.Concurrent.newForeignPtr]
is used, here's a case where the finalizer is called twice:
{{{
{-# LANGUAGE ForeignFunctionInterface #-}
import Control.Concurrent
import Control.Exception (bracket)
import Foreign.Ptr (Ptr, intPtrToPtr)
import Foreign.ForeignPtr (ForeignPtr)
import qualified Foreign.Concurrent as FC
import qualified Foreign.ForeignPtr as FP
testForeignPtr_Concurrent :: Ptr a -> IO (ForeignPtr a)
testForeignPtr_Concurrent ptr = FC.newForeignPtr ptr (fin ptr)
fin :: Ptr a -> IO ()
fin ptr = putStrLn $ "finalizing " ++ show ptr
main :: IO ()
main = do
mv <- newEmptyMVar
bracket (testForeignPtr_Concurrent $ intPtrToPtr 1)
FP.finalizeForeignPtr $ \_ ->
-- hang, so the thread and foreign pointer get GCed
takeMVar mv
}}}
This produces the following output:
{{{
finalizing 0x0000000000000001
finalizing 0x0000000000000001
foreignptr: thread blocked indefinitely in an MVar operation
}}}
This happens on GHC 7.4.2 and 7.6.0.20120810, with and without -threaded.
This can easily lead to segfaults when you have an FFI library that does
this:
{{{
create :: IO Object
create = do
ptr <- c_create
CObject <$> newForeignPtr ptr (finalize ptr)
finalize :: Ptr CObject -> IO ()
finalize ptr = do
...
destroy :: Object -> IO ()
destroy (Object fptr) =
finalizeForeignPtr fptr
}}}
And application code does this:
{{{
bracket create destroy $ \obj -> do
...
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7170>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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