Portability | non-portable (uses GHC extensions) |
---|---|
Maintainer | lemmih@gmail.com |
Safe Haskell | None |
AcidState container using a transaction log on disk.
To see how it all fits together, have a look at these example http://mirror.seize.it/acid-state/examples/.
- data AcidState st
- openLocalState :: (Typeable st, IsAcidic st) => st -> IO (AcidState st)
- openLocalStateFrom :: IsAcidic st => FilePath -> st -> IO (AcidState st)
- closeAcidState :: AcidState st -> IO ()
- createCheckpoint :: AcidState st -> IO ()
- createArchive :: AcidState st -> IO ()
- update :: UpdateEvent event => AcidState (EventState event) -> event -> IO (EventResult event)
- query :: QueryEvent event => AcidState (EventState event) -> event -> IO (EventResult event)
- type EventResult ev = MethodResult ev
- type EventState ev = MethodState ev
- class Method ev => UpdateEvent ev
- class Method ev => QueryEvent ev
- data Update st a
- data Query st a
- class SafeCopy st => IsAcidic st
- makeAcidic :: Name -> [Name] -> Q [Dec]
- liftQuery :: Query st a -> Update st a
Documentation
State container offering full ACID (Atomicity, Consistency, Isolation and Durability) guarantees.
Atomicity
- State changes are all-or-nothing. This is what you'd expect of any state variable in Haskell and AcidState doesn't change that.
Consistency
- No event or set of events will break your data invariants.
Isolation
- Transactions cannot interfere with each other even when issued in parallel.
Durability
- Successful transaction are guaranteed to survive unexpected system shutdowns (both those caused by hardware and software).
:: (Typeable st, IsAcidic st) | |
=> st | Initial state value. This value is only used if no checkpoint is found. |
-> IO (AcidState st) |
Create an AcidState given an initial value.
This will create or resume a log found in the "state/[typeOf state]/" directory.
:: IsAcidic st | |
=> FilePath | Location of the checkpoint and transaction files. |
-> st | Initial state value. This value is only used if no checkpoint is found. |
-> IO (AcidState st) |
Create an AcidState given a log directory and an initial value.
This will create or resume a log found in directory
.
Running two AcidState's from the same directory is an error
but will not result in dataloss.
closeAcidState :: AcidState st -> IO ()Source
Close an AcidState and associated resources. Any subsequent usage of the AcidState will throw an exception.
createCheckpoint :: AcidState st -> IO ()Source
Take a snapshot of the state and save it to disk. Creating checkpoints makes it faster to resume AcidStates and you're free to create them as often or seldom as fits your needs. Transactions can run concurrently with this call.
This call will not return until the operation has succeeded.
createArchive :: AcidState st -> IO ()Source
update :: UpdateEvent event => AcidState (EventState event) -> event -> IO (EventResult event)Source
Issue an Update event and wait for its result. Once this call returns, you are guaranteed that the changes to the state are durable. Events may be issued in parallel.
It's a run-time error to issue events that aren't supported by the AcidState.
query :: QueryEvent event => AcidState (EventState event) -> event -> IO (EventResult event)Source
Issue a Query event and wait for its result. Events may be issued in parallel.
type EventResult ev = MethodResult evSource
Events return the same thing as Methods. The exact type of EventResult
depends on the event.
type EventState ev = MethodState evSource
class Method ev => UpdateEvent ev Source
All UpdateEvents are also Methods.
class Method ev => QueryEvent ev Source
All QueryEvents are also Methods.
Context monad for Update events.
MonadState st (Update st) | |
Monad (Update st) | |
Functor (Update st) | |
Applicative (Update st) |
Context monad for Query events.
MonadReader st (Query st) | |
Monad (Query st) | |
Functor (Query st) | |
Applicative (Query st) |
makeAcidic :: Name -> [Name] -> Q [Dec]Source
Create the control structures required for acid states using Template Haskell.
This code:
myUpdate :: Argument -> Update State Result myUpdate arg = ... myQuery :: Argument -> Query State Result myQuery arg = ... $(makeAcidic ''State ['myUpdate, 'myQuery])
will make State
an instance of IsAcidic
and provide the following
events:
data MyUpdate = MyUpdate Argument data MyQuery = MyQuery Argument