Data.Acid.Core

Low-level controls for transaction-based state changes. This module defines structures and tools for running state modifiers indexed either by an Method or a serialized Method. This module should rarely be used directly although the Method class is needed when defining events manually.

The term 'Event' is loosely used for transactions with ACID guarantees. 'Method' is loosely used for state operations without ACID guarantees

Documentation

data Core st

The control structure at the very center of acid-state. This module provides access to a mutable state through methods. No efforts towards durability, checkpointing or sharding happens at this level. Important things to keep in mind in this module: * We don't distinguish between updates and queries. * We allow direct access to the core state as well as through events.

class Method ev where

The basic Method class. Each Method has an indexed result type and a unique tag.

Minimal complete definition

Nothing

Associated Types

type MethodResult ev

type MethodState ev

Methods

methodTag :: ev -> Tag

default methodTag :: Typeable ev => ev -> Tag

data MethodContainer st where

Method container structure that hides the exact type of the method.

Constructors

Method :: Method method => MethodBody method -> MethodSerialiser method -> MethodContainer (MethodState method)

type Tagged a = (Tag, a)

mkCore

Arguments

:: [MethodContainer st]

List of methods capable of modifying the state.

-> st

Initial state value.

-> IO (Core st)

Construct a new Core using an initial state and a list of Methods.

closeCore :: Core st -> IO ()

Mark Core as closed. Any subsequent use will throw an exception.

closeCore' :: Core st -> (st -> IO ()) -> IO ()

Access the state and then mark the Core as closed. Any subsequent use will throw an exception.

modifyCoreState :: Core st -> (st -> IO (st, a)) -> IO a

Modify the state component. The resulting state is ensured to be in WHNF.

modifyCoreState_ :: Core st -> (st -> IO st) -> IO ()

Modify the state component. The resulting state is ensured to be in WHNF.

withCoreState :: Core st -> (st -> IO a) -> IO a

Access the state component.

lookupHotMethod :: Method method => MethodMap (MethodState method) -> method -> State (MethodState method) (MethodResult method)

Find the state action that corresponds to an in-memory method.

lookupHotMethodAndSerialiser :: Method method => MethodMap (MethodState method) -> method -> (State (MethodState method) (MethodResult method), MethodSerialiser method)

Find the state action and serialiser that correspond to an in-memory method.

lookupColdMethod :: Core st -> Tagged ByteString -> State st ByteString

Find the state action that corresponds to a tagged and serialized method.

runHotMethod :: Method method => Core (MethodState method) -> method -> IO (MethodResult method)

Apply an in-memory method to the state.

runColdMethod :: Core st -> Tagged ByteString -> IO ByteString

Execute a method as given by a type identifier and an encoded string. The exact format of the encoded string depends on the type identifier. Results are encoded and type tagged before they're handed back out. This function is used when running events from a log-file or from another server. Events that originate locally are most likely executed with the faster runHotMethod.

type MethodMap st = Map Tag (MethodContainer st)

Collection of Methods indexed by a Tag.

mkMethodMap :: [MethodContainer st] -> MethodMap st

Construct a MethodMap from a list of Methods using their associated tag.

data Serialiser a

Interface for (de)serialising values of type a.

A Serialiser { serialiserEncode, serialiserDecode } must satisfy the round-trip property:

forall x . serialiserDecode (serialiserEncode x) == Right x

Constructors

Serialiser

Fields

• serialiserEncode :: a -> ByteString

  Serialise a value to a bytestring.

• serialiserDecode :: ByteString -> Either String a

  Deserialise a value, generating a string error message on failure.

safeCopySerialiser :: SafeCopy a => Serialiser a

Default implementation of Serialiser interface using SafeCopy.

data MethodSerialiser method

Interface for (de)serialising a method, namely Serialisers for its arguments type and its result type.

Constructors

MethodSerialiser

Fields

• methodSerialiser :: Serialiser method
• resultSerialiser :: Serialiser (MethodResult method)

safeCopyMethodSerialiser :: (SafeCopy method, SafeCopy (MethodResult method)) => MethodSerialiser method

Default implementation of MethodSerialiser interface using SafeCopy.

encodeMethod :: MethodSerialiser method -> method -> ByteString

Encode the arguments of a method using the given serialisation strategy.

decodeMethod :: MethodSerialiser method -> ByteString -> Either String method

Decode the arguments of a method using the given serialisation strategy.

encodeResult :: MethodSerialiser method -> MethodResult method -> ByteString

Encode the result of a method using the given serialisation strategy.

decodeResult :: MethodSerialiser method -> ByteString -> Either String (MethodResult method)

Decode the result of a method using the given serialisation strategy.