throwTo to a thread inside 'block'
[copy-pasting my original mail (http://www.haskell.org/pipermail/glasgow-haskell-bugs/2005-June/005235.html)\]
I just stumbled across a segfault caused when running the following small program. (During an attempt to implement single-assignment variables.)
> module Main where > > import Control.Concurrent > import System.IO.Unsafe (unsafeInterleaveIO) > > main = do > v <- newEmptyMVar > a <- unsafeInterleaveIO (readMVar v) > t <- forkIO (print a) > threadDelay (1000*1000) > killThread t > forkIO (print a) > putMVar v ()
The crucial part about it seems to be the interruption of the lazy IO. Typing Ctl-c while running the first "print a" by hand from ghci instead of the forkIO+killThread doesn't change behaviour:
Prelude System.IO.Unsafe Control.Concurrent> v <- newEmptyMVar Prelude System.IO.Unsafe Control.Concurrent> a <- unsafeInterleaveIO (readMVar v) Prelude System.IO.Unsafe Control.Concurrent> print a Interrupted. Prelude System.IO.Unsafe Control.Concurrent> forkIO (print a) Prelude System.IO.Unsafe Control.Concurrent> putMVar v () zsh: segmentation fault (core dumped) ghci
Both 6.4 and 6.2.1 crash when running main from ghci. When running it as a compiled executable everything is fine.
Although I'm pretty sure I've seen 6.2.1 crashing on it when run with -e main, I cannot reproduce it anymore. 6.4 certainly happily runs it with -e main. (A serious lack of sleep the last week may play a role too.. :-/)
Whether the module is compiled before being loaded into ghci has no effect.
Core-dumps etc can of course be sent if necessary.
Good night, Remi