Portability | non-portable (requires STM) |
---|---|
Stability | experimental |
Maintainer | Peter Robinson <robinson@ecs.tuwien.ac.at> |
Provides the type class MonadAdvSTM and the AdvSTM monad. Parts of this implementation were taken from the HaskellWiki Page of MonadAdvSTM (see package description).
- class Monad m => MonadAdvSTM m where
- data AdvSTM a
Documentation
class Monad m => MonadAdvSTM m whereSource
A type class for extended-STM monads. For a concrete instantiation see
AdvSTM
onCommit :: IO () -> m ()Source
Takes an IO action that will be executed iff the transaction commits.
- When a TVar was modified in a transaction and this transaction commits, this update remains invisible to other threads until the corresponding onCommit action was run.
- If the onCommit action throws an exception, the original value of the TVars will be restored.
- Accessing a modified TVar within the onCommit action will cause a
Deadlock
exception to be thrown.
As a general rule, onCommit
should
only be used for "real" (i.e. without atomic blocks) IO actions and is certainly
not the right place to fiddle with TVars. For example, if you wanted to
write a TVar value to a file on commit, you could write:
tvar <- newTVarIO "bla" atomically $ do x <- readTVar tvar onCommit (writeFile "myfile" x)
unsafeOnRetry :: IO () -> m ()Source
Adds an IO action to the retry job-queue. If the transaction retries, a new helper thread is forked that runs the retry actions, and, after the helper thread is done, the transaction retries. Warning: Uses unsafeIOToSTM to fork a helper thread that runs the retry actions!
orElse :: m a -> m a -> m aSource
See orElse
See retry
. Skips any IO actions added by unsafeOnRetry.
See check
alwaysSucceeds :: m a -> m ()Source
See alwaysSucceeds
always :: m Bool -> m ()Source
See always
runAtomic :: m a -> IO aSource
Runs a transaction atomically in the IO
monad.
catchSTM :: Exception e => m a -> (e -> m a) -> m aSource
See catchSTM
Lifts STM actions to MonadAdvSTM
.