#5866: Interrupting interleaved STM and resuming it produces segfault
------------------------------+---------------------------------------------
Reporter: joeyadams | Owner:
Type: bug | Status: new
Priority: normal | Component: Runtime System
Version: 7.4.1 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: Runtime crash | Testcase:
Blockedby: | Blocking:
Related: |
------------------------------+---------------------------------------------
The following program produces a segfault:
{{{
import Control.Concurrent.STM
import Control.Exception
import System.IO.Unsafe
import System.Timeout
main :: IO ()
main = do
x <- unsafeInterleaveIO $ atomically retry
_ <- timeout 1000000 $ evaluate x
evaluate x
}}}
When a thread is interrupted while evaluating interleaved IO, and that IO
is blocked on an STM transaction, resuming the suspended computation
produces a segfault.
This segfault happens with GHC 7.0.3, 7.2.2, and 7.4.1, on both Windows
32-bit and Linux 64-bit, with and without -threaded.
Compiling with -debug on 7.5.20120211, I get an assertion failure in
rts/STM.c, line 1525:
{{{
ASSERT (trec != NO_TREC);
}}}
In general, pure computations are not always suspended by asynchronous
exceptions:
{{{
import Control.Concurrent
import System.IO.Unsafe
import System.Timeout
main :: IO ()
main = do
-- Resuming interleaved takeMVar works correctly
mv <- newEmptyMVar
_ <- forkIO $ threadDelay 2000000 >> putMVar mv "Hello"
s <- unsafeInterleaveIO $ takeMVar mv
_ <- timeout 1000000 $ putStrLn s
putStrLn s
-- But resuming getLine repeats the asynchronous exception, contrary
to the
-- documentation of 'throwTo'
s <- unsafeInterleaveIO getLine
_ <- timeout 1000000 $ putStrLn s
putStrLn s
}}}
Note issue #5859 when testing: unsafeInterleaveIO being INLINE causes
computations to be duplicated when shared among threads. The examples
above dodge this issue by keeping the work in the current thread.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5866>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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