[Haskell-cafe] STM commit hooks
ekarttun at cs.helsinki.fi
Tue Nov 29 07:39:46 EST 2005
I have been playing with STM and want to log transactions to disk.
Defining a logging function like:
log h act = unsafeIOToSTM $ hPrint h act
works most the time. Aborts can be handled with:
abort h = log h Abort >> retry
atomic' h act = atomically (act `orElse` abort h)
But is it possible to handle a commit?
commit h = unsafeIOToSTM (hPrint h Commit >> hSync h)
atomically2 h act = atomically ((act >> commit h) `orElse` abort h)
This won't work because the transaction is validated and
maybe aborted after the commit is logged to disk.
Another alternative would be:
atomically3 h act = atomically (act `orElse` abort h) >> atomically (commit h)
But this does not work either. Given Trx1 and Trx2, the following may occur:
1) Trx1 commits
2) Trx2 commits (and depends on Trx1)
3) Trx2 commit is logged to disk
This means that the log would be inconsistent. Is there a way to implement
the commit that works?
- Einar Karttunen
More information about the Haskell-Cafe