| Copyright | (c) 2016 Michael Walker |
|---|---|
| License | MIT |
| Maintainer | Michael Walker <[email protected]> |
| Stability | experimental |
| Portability | CPP, RankNTypes, TemplateHaskell, TypeFamilies |
| Safe Haskell | Safe |
| Language | Haskell2010 |
Control.Monad.STM.Class
Contents
Description
This module provides an abstraction over STM, which can be used
with MonadConc.
This module only defines the STM class; you probably want to
import Control.Concurrent.Classy.STM (which exports
Control.Monad.STM.Class).
Deviations: An instance of MonadSTM is not required to be an
Alternative, MonadPlus, and MonadFix, unlike STM. The
always and alwaysSucceeds functions are not provided; if you
need these file an issue and I'll look into it.
- class MonadCatch stm => MonadSTM stm where
- check :: MonadSTM stm => Bool -> stm ()
- throwSTM :: (MonadSTM stm, Exception e) => e -> stm a
- catchSTM :: (MonadSTM stm, Exception e) => stm a -> (e -> stm a) -> stm a
- liftedOrElse :: (MonadTransControl t, MonadSTM stm) => (forall x. StT t x -> x) -> t stm a -> t stm a -> t stm a
Documentation
class MonadCatch stm => MonadSTM stm where Source #
MonadSTM is an abstraction over STM.
This class does not provide any way to run transactions, rather
each MonadConc has an associated MonadSTM from which it can
atomically run a transaction.
Associated Types
type TVar stm :: * -> * Source #
The mutable reference type. These behave like TVars, in that
they always contain a value and updates are non-blocking and
synchronised.
Methods
Retry execution of this transaction because it has seen values
in TVars that it shouldn't have. This will result in the
thread running the transaction being blocked until any TVars
referenced in it have been mutated.
orElse :: stm a -> stm a -> stm a Source #
Run the first transaction and, if it retrys, run the second
instead. If the monad is an instance of
'Alternative'/'MonadPlus', orElse should be the '(|)'/'mplus'
function.
newTVar :: a -> stm (TVar stm a) Source #
Create a new TVar containing the given value.
newTVar = newTVarN ""
newTVarN :: String -> a -> stm (TVar stm a) Source #
Create a new TVar containing the given value, but it is
given a name which may be used to present more useful debugging
information.
If an empty name is given, a counter starting from 0 is used. If
names conflict, successive TVars with the same name are given
a numeric suffix, counting up from 1.
newTVarN _ = newTVar
readTVar :: TVar stm a -> stm a Source #
Return the current value stored in a TVar.
writeTVar :: TVar stm a -> a -> stm () Source #
Write the supplied value into the TVar.
Instances
| MonadSTM STM Source # | |
| MonadSTM stm => MonadSTM (StateT s stm) Source # | |
| MonadSTM stm => MonadSTM (StateT s stm) Source # | |
| (MonadSTM stm, Monoid w) => MonadSTM (WriterT w stm) Source # | |
| (MonadSTM stm, Monoid w) => MonadSTM (WriterT w stm) Source # | |
| MonadSTM stm => MonadSTM (IdentityT * stm) Source # | |
| MonadSTM stm => MonadSTM (ReaderT * r stm) Source # | |
| (MonadSTM stm, Monoid w) => MonadSTM (RWST r w s stm) Source # | |
| (MonadSTM stm, Monoid w) => MonadSTM (RWST r w s stm) Source # | |
check :: MonadSTM stm => Bool -> stm () Source #
Check whether a condition is true and, if not, call retry.
throwSTM :: (MonadSTM stm, Exception e) => e -> stm a Source #
Throw an exception. This aborts the transaction and propagates the exception.
catchSTM :: (MonadSTM stm, Exception e) => stm a -> (e -> stm a) -> stm a Source #
Handling exceptions from throwSTM.
Utilities for instance writers
liftedOrElse :: (MonadTransControl t, MonadSTM stm) => (forall x. StT t x -> x) -> t stm a -> t stm a -> t stm a Source #
Given a function to remove the transformer-specific state, lift
an orElse invocation.