BlockingTransactions.BlockingTransactions

Composable blocking transactions, based on the blog post: http://blog.downstairspeople.org/2010/06/06/composable-blocking-transactions/

Transactional Variables

data BVar a

A transactional variable with a blocking implementation.

Instances

Eq (BVar a)

Ord (BVar a)

newBVar :: a -> IO (BVar a)

Construct a new transactional variable.

peekBVar :: BVar a -> IO a

Observe the contents of a transactional variable.

pokeBVar :: BVar a -> a -> IO ()

One-off write to a transactional variable.

modifyBVar :: BVar a -> (a -> (a, b)) -> IO b

Perform a transaction using only a single variable.

Blocking Transaction Monad

runBTM :: (forall e. BTM e (Value e a)) -> IO a

Commit a blocking transaction.

data BTM e a

The blocking transaction monad.

Instances

Monad (BTM e)

Functor (BTM e)

Applicative (BTM e)

data Value e a

An opaque value. It can be modified and combined with other opaque values, but not observed.

The type variable e binds the value to the monadic context in which it occurs, (this is identical to the runST existential type trick).

Instances

Monad (Value e)

Functor (Value e)

Applicative (Value e)

when :: Value e Bool -> BTM e (Value e ()) -> BTM e (Value e ())

Flow control. Skip the critical section if the predicate is false.

unless :: Value e Bool -> BTM e (Value e ()) -> BTM e (Value e ())

Flow control. Skip the critical section if the predicate is true.

readBVar :: BVar a -> BTM e (Value e a)

Read from a variable.

writeBVar :: BVar a -> Value e a -> BTM e (Value e ())

Write to a variable.

retry :: BTM e (Value e ())

Electively retry. This will restore all variables to their state before the transaction began, and listen for a change to any variable in the working set before trying the transaction again.

Blocking Transaction Arrow

runBTA :: BTA a b -> a -> IO b

data BTA a b

The blocking transaction arrow. The semantics are identical to the equivalent operations on the monadic interface.

Instances

Arrow BTA

ArrowChoice BTA

Category BTA

Functor (BTA a)

Applicative (BTA a)

fetchBVar :: BVar a -> BTA () a

As writeBVar.

storeBVar :: BVar a -> BTA a ()

As readBVar.

retryWhen :: BTA Bool ()

As retry.

retryUnless :: BTA Bool ()