Re: STM and unsafePerformIO
Oh I see! Your sollutions are indeed a lot better than implementating all my code using MVars :-). Thanks, Robert Remi Turk wrote: On Wed, Aug 03, 2005 at 12:50:54PM +0200, Robert van Herk wrote: Hello All, I think I've read somewhere that STM doesn't like unsafePerformIO. However, I would like to use a global STM variable. Something like this: module Main where import GHC.Conc import System.IO.Unsafe tSid = unsafePerformIO (atomically (newTVar 0)) tickSessionID :: STM Int tickSessionID = do sid <- readTVar tSid writeTVar tSid (sid + 1) return sid main = atomically tickSessionID But, when I try this, the evaluation of main causes a segmentation fault. Is there a workaround for this bug? Regards, Robert It probably dies not because of unsafePerformIO per se, but because STM doesn't understand nested transactions, and unsafePerformIO here results in a nested transaction. Using the following main works for me, as it forces both "atomically"'s to be evaluated sequentially: main = tSid `seq` atomically tickSessionID See also http://haskell.org/pipermail/glasgow-haskell-users/2005-June/008615.html and http://sourceforge.net/tracker/index.php?func=detail&aid=1235728&group_id=8032&atid=108032 Happy hacking, Remi P.S. Could you find out (and fix) what inserts those spurious *'s in your code? ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
RE: STM and unsafePerformIO
On 03 August 2005 11:51, Robert van Herk wrote: > I think I've read somewhere that STM doesn't like unsafePerformIO. > However, I would like to use a global STM variable. Something like > this: > > *module* Main *where* > import GHC.Conc > import System.IO.Unsafe > > tSid = unsafePerformIO (atomically (newTVar 0)) > > tickSessionID :: STM Int > tickSessionID = > *do* sid <- readTVar tSid > writeTVar tSid (sid + 1) > return sid > > main = atomically tickSessionID > > But, when I try this, the evaluation of main causes a segmentation > fault. Is there a workaround for this bug? You're ok as long as the global variable doesn't get evaluated inside another atomically. The problem is that nested atomically isn't supported; the RTS gets confused. For example, you could say main = do evaluate tSid ... to force evaluation of tSid before doing anything else. Cheers, Simon ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: STM and unsafePerformIO
On Wed, Aug 03, 2005 at 12:50:54PM +0200, Robert van Herk wrote: > Hello All, > > I think I've read somewhere that STM doesn't like unsafePerformIO. > However, I would like to use a global STM variable. Something like this: > > module Main where > import GHC.Conc > import System.IO.Unsafe > > tSid = unsafePerformIO (atomically (newTVar 0)) > > tickSessionID :: STM Int > tickSessionID = > do sid <- readTVar tSid > writeTVar tSid (sid + 1) > return sid > > main = atomically tickSessionID > > > > But, when I try this, the evaluation of main causes a segmentation > fault. Is there a workaround for this bug? > > Regards, > Robert It probably dies not because of unsafePerformIO per se, but because STM doesn't understand nested transactions, and unsafePerformIO here results in a nested transaction. Using the following main works for me, as it forces both "atomically"'s to be evaluated sequentially: main = tSid `seq` atomically tickSessionID See also http://haskell.org/pipermail/glasgow-haskell-users/2005-June/008615.html and http://sourceforge.net/tracker/index.php?func=detail&aid=1235728&group_id=8032&atid=108032 Happy hacking, Remi P.S. Could you find out (and fix) what inserts those spurious *'s in your code? -- Nobody can be exactly like me. Even I have trouble doing it. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: STM and unsafePerformIO
Never mind, I can probably use an MVar to work around this... Robert Robert van Herk wrote: Hello All, I think I've read somewhere that STM doesn't like unsafePerformIO. However, I would like to use a global STM variable. Something like this: module Main where import GHC.Conc import System.IO.Unsafe tSid = unsafePerformIO (atomically (newTVar 0)) tickSessionID :: STM Int tickSessionID = do sid <- readTVar tSid writeTVar tSid (sid + 1) return sid main = atomically tickSessionID But, when I try this, the evaluation of main causes a segmentation fault. Is there a workaround for this bug? Regards, Robert ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
