Control.Monad.AdvSTM

Provides the type class MonadAdvSTM and the AdvSTM monad. Parts of this implementation were taken from the HaskellWiki Page of MonadAdvSTM (see package description).

Documentation

class Monad m => MonadAdvSTM m where

A type class for extended-STM monads. For a concrete instantiation see AdvSTM

Methods

onCommit :: IO () -> m ()

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

Arguments

:: IO ()

IO action that will be run on retry the transaction.

-> m ()

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.

Uses unsafeIOToSTM to fork a helper thread that runs the retry actions.

orElse :: m a -> m a -> m a

See orElse

retry :: m a

Runs any IO actions added by unsafeOnRetry and then retries the transaction.

check :: Bool -> m ()

See check

alwaysSucceeds :: m a -> m ()

See alwaysSucceeds

always :: m Bool -> m ()

See always

runAtomic :: m a -> IO a

Runs a transaction atomically in the IO monad.

catchSTM :: Exception e => m a -> (e -> m a) -> m a

See catchSTM

liftAdv :: STM a -> m a

Lifts STM actions to MonadAdvSTM.

readTVar :: TVar a -> m a

Reads a value from a TVar. Blocks until the IO onCommit action(s) of the corresponding transaction are complete. See onCommit for a more detailed description of this behaviour.

writeTVar :: TVar a -> a -> m ()

Writes a value to a TVar. Blocks until the onCommit IO-action(s) are complete. See onCommit for details.

newTVar :: a -> m (TVar a)

See newTVar

Instances

MonadAdvSTM AdvSTM

data AdvSTM a

Drop-in replacement for the STM monad

Instances

Monad AdvSTM

Functor AdvSTM

MonadPlus AdvSTM

MonadAdvSTM AdvSTM