|Portability||non-portable (requires STM)|
|Maintainer||Peter Robinson <firstname.lastname@example.org>|
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
- onCommit :: IO () -> m ()
- unsafeRetryWith :: IO () -> m b
- orElse :: m a -> m a -> m a
- retry :: m a
- check :: Bool -> m ()
- alwaysSucceeds :: m a -> m ()
- always :: m Bool -> m ()
- catchSTM :: Exception e => m a -> (e -> m a) -> m a
- liftAdv :: STM a -> m a
- readTVar :: TVar a -> m a
- writeTVar :: TVar a -> a -> m ()
- readTVarAsync :: TVar a -> m a
- writeTVarAsync :: TVar a -> a -> m ()
- newTVar :: a -> m (TVar a)
- data AdvSTM a
A type class for extended-STM monads. For a concrete instantiation see
Takes an IO action that will be executed iff the transaction commits.
- When a TVar was modified in a transaction and the transaction tries to commit, this update remains invisible to other threads until the corresponding onCommit action is dispatched.
- 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,
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)
Retries the transaction and uses
unsafeIOToSTM to fork off a
thread that runs the given IO action. Since a transaction might be rerun
several times by the runtime system, it is your responsibility to
ensure that the IO-action is idempotent and releases all acquired locks.
Lifts STM actions to
Reads a value from a TVar. Blocks until the IO onCommit action(s) of
the corresponding transaction are complete.
onCommit for a more detailed description of this behaviour.
Writes a value to a TVar. Blocks until the onCommit IO-action(s) are
onCommit for details.
Reads a value directly from the TVar. Does not block when the onCommit actions aren't done yet. NOTE: Only use this function when you know what you're doing.
Writes a value directly to the TVar. Does not block when onCommit actions aren't done yet. This function comes in handy for error recovery of exceptions that occur in onCommit.