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+That's all there is to it!
2 Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
153 bin/synod.hs
@@ -0,0 +1,153 @@
+{- Paxos - Implementations of Paxos-related consensus algorithms
+ -
+ - Copyright (C) 2012 Nicolas Trangez
+ -
+ - This library is free software; you can redistribute it and/or
+ - modify it under the terms of the GNU Lesser General Public
+ - License as published by the Free Software Foundation; either
+ - version 2.1 of the License, or (at your option) any later version.
+ -
+ - This library is distributed in the hope that it will be useful,
+ - but WITHOUT ANY WARRANTY; without even the implied warranty of
+ - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ - Lesser General Public License for more details.
+ -
+ - You should have received a copy of the GNU Lesser General Public
+ - License along with this library; if not, write to the Free Software
+ - Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
+ - USA.
+ -}
+
+module Main (main) where
+
+import Control.Monad
+import Control.Applicative
+
+import Control.Concurrent
+import Control.Concurrent.STM
+
+import System.Random
+
+import Network.Paxos.Synod
+import qualified Network.Paxos.Synod.Proposer as P
+import qualified Network.Paxos.Synod.Acceptor as A
+import qualified Network.Paxos.Synod.Learner as L
+
+-- TODO Use System.Logger or something alike and log inside run* actions
+-- TODO Implement lossy and duplicating channels (and update code
+-- accordingly: restart a new round after a certain timeout etc)
+
+type NodeId = String
+type Value = String
+type Actions = [Action NodeId Value]
+type NetworkChannel = TChan (NodeId, Action NodeId Value)
+type MessageChannel = TChan (NodeId, Message NodeId Value)
+
+-- | A version of readTChan which adds some random delay before returning
+-- the actual message
+readTChan' :: TChan a -> IO a
+readTChan' chan = do
+ delay <- (`rem` 2000000) <$> randomIO
+ threadDelay delay
+ atomically $ readTChan chan
+
+handleActions :: NodeId -> NetworkChannel -> Actions -> IO ()
+handleActions name network = atomically . mapM_ (\a -> writeTChan network (name, a))
+
+runProposer :: Quorum -> P.ProposalId NodeId -> Value -> MessageChannel -> NetworkChannel -> IO ()
+runProposer q p v chan network = do
+ handleActions "proposer" network actions0
+ loop state0
+ where
+ (state0, actions0) = P.startRound q p v
+ loop state = do
+ (sender, msg) <- atomically $ readTChan chan
+ case msg of
+ MsgPromise m -> do
+ let (state', actions) = P.handlePromise state sender m
+ handleActions "proposer" network actions
+ loop state'
+ _ -> loop state
+
+runAcceptor :: Int -> MessageChannel -> NetworkChannel -> IO ()
+runAcceptor i chan network = loop state0
+ where
+ state0 = A.initialize
+ loop state = do
+ (sender, msg) <- readTChan' chan
+ case msg of
+ MsgPrepare m -> do
+ let (state', actions) = A.handlePrepare state sender m
+ handleActions ("acceptor" ++ show i) network actions
+ loop state'
+ MsgAccept m -> do
+ let (state', actions) = A.handleAccept state m
+ handleActions ("acceptor" ++ show i) network actions
+ loop state'
+ _ -> loop state
+
+runLearner :: Int -> Quorum -> MessageChannel -> NetworkChannel -> MVar Value -> IO ()
+runLearner _i q chan _network lock = loop state0
+ where
+ state0 = L.initialize q
+ loop state = do
+ (sender, msg) <- readTChan' chan
+ case msg of
+ MsgAccepted m -> do
+ let state' = L.handleAccepted state sender m
+ case L.getValue state' of
+ Nothing -> loop state'
+ Just v -> putMVar lock v
+ _ -> loop state
+
+runNetwork :: NetworkChannel -> MessageChannel -> MessageChannel -> MessageChannel -> IO ()
+runNetwork chan proposer acceptors learners = forever loop
+ where
+ loop = do
+ (sender, action) <- atomically $ readTChan chan
+ putStrLn $ sender ++ ": " ++ show action
+ case action of
+ Send target message -> if target == "proposer"
+ then atomically $ writeTChan proposer (sender, message)
+ else error $ "Unknown target '" ++ target ++ "'"
+ Broadcast group message -> case group of
+ Acceptors -> atomically $ writeTChan acceptors (sender, message)
+ Learners -> atomically $ writeTChan learners (sender, message)
+
+
+main :: IO ()
+main = do
+ proposerChan <- newTChanIO
+ acceptorsChan <- newBroadcastTChanIO
+ learnersChan <- newBroadcastTChanIO
+
+ network <- newTChanIO
+
+ lock <- newEmptyMVar
+
+ networkHandler <- forkIO $ runNetwork network proposerChan acceptorsChan learnersChan
+
+ learners <- forM [0 .. numLearners - 1] $ \i -> do
+ chan <- atomically $ dupTChan learnersChan
+ forkIO $ runLearner i q chan network lock
+
+ acceptors <- forM [0 .. numAcceptors - 1] $ \i -> do
+ chan <- atomically $ dupTChan acceptorsChan
+ forkIO $ runAcceptor i chan network
+
+ proposer <- forkIO $ runProposer q (P.initialProposalId "proposer") "Hello, world!" proposerChan network
+
+ result <- takeMVar lock
+
+ mapM_ killThread acceptors
+ mapM_ killThread learners
+ killThread proposer
+ killThread networkHandler
+
+ putStrLn $ "Learned value: " ++ result
+
+ where
+ numLearners, numAcceptors :: Int
+ numLearners = 2
+ numAcceptors = 5
+ q = quorum $ numAcceptors `div` 2 + 1
32 bin/tests.hs
@@ -0,0 +1,32 @@
+{- Paxos - Implementations of Paxos-related consensus algorithms
+ -
+ - Copyright (C) 2012 Nicolas Trangez
+ -
+ - This library is free software; you can redistribute it and/or
+ - modify it under the terms of the GNU Lesser General Public
+ - License as published by the Free Software Foundation; either
+ - version 2.1 of the License, or (at your option) any later version.
+ -
+ - This library is distributed in the hope that it will be useful,
+ - but WITHOUT ANY WARRANTY; without even the implied warranty of
+ - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ - Lesser General Public License for more details.
+ -
+ - You should have received a copy of the GNU Lesser General Public
+ - License along with this library; if not, write to the Free Software
+ - Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
+ - USA.
+ -}
+
+module Main (main) where
+
+import Test.Framework (Test, defaultMain)
+
+import qualified Network.Paxos.Synod
+
+main :: IO ()
+main = defaultMain tests
+
+tests :: [Test]
+tests = [ Network.Paxos.Synod.tests
+ ]
47 paxos.cabal
@@ -0,0 +1,47 @@
+Name: paxos
+Version: 0.1.0.0
+Synopsis: Implementations of Paxos-related consensus algorithms
+-- Description:
+Homepage: http://github.com/NicolasT/Paxos
+License: LGPL-2.1
+License-File: LICENSE
+Author: Nicolas Trangez
+Maintainer: ikke@nicolast.be
+Copyright: Copyright (c) 2012, Nicolas Trangez
+Category: Network
+Build-Type: Simple
+Cabal-Version: >=1.8
+
+Library
+ Exposed-Modules: Network.Paxos.Synod,
+ Network.Paxos.Synod.Proposer,
+ Network.Paxos.Synod.Acceptor,
+ Network.Paxos.Synod.Learner
+ Other-Modules: Network.Paxos.Synod.Action,
+ Network.Paxos.Synod.Types,
+ Network.Paxos.Synod.Messages
+ Build-Depends: base >= 4 && < 5,
+ containers,
+ QuickCheck >= 2,
+ test-framework,
+ test-framework-quickcheck2
+ Hs-Source-Dirs: src
+ Ghc-Options: -Wall -fwarn-incomplete-patterns
+
+Executable synod
+ Main-Is: synod.hs
+ Build-Depends: base >= 4 && < 5,
+ stm,
+ random,
+ paxos
+ Hs-Source-Dirs: bin
+ Ghc-Options: -Wall -fwarn-incomplete-patterns -rtsopts -threaded
+
+Test-Suite tests
+ Type: exitcode-stdio-1.0
+ Main-Is: tests.hs
+ Build-Depends: base >= 4 && < 5,
+ test-framework,
+ paxos
+ Hs-Source-Dirs: bin
+ Ghc-Options: -Wall -fwarn-incomplete-patterns -rtsopts -threaded
50 src/Network/Paxos/Synod.hs
@@ -0,0 +1,50 @@
+{- Paxos - Implementations of Paxos-related consensus algorithms
+ -
+ - Copyright (C) 2012 Nicolas Trangez
+ -
+ - This library is free software; you can redistribute it and/or
+ - modify it under the terms of the GNU Lesser General Public
+ - License as published by the Free Software Foundation; either
+ - version 2.1 of the License, or (at your option) any later version.
+ -
+ - This library is distributed in the hope that it will be useful,
+ - but WITHOUT ANY WARRANTY; without even the implied warranty of
+ - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ - Lesser General Public License for more details.
+ -
+ - You should have received a copy of the GNU Lesser General Public
+ - License along with this library; if not, write to the Free Software
+ - Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
+ - USA.
+ -}
+
+module Network.Paxos.Synod (
+ -- * Re-exports
+ BroadcastGroup(..)
+ , Action(..)
+ , Message(..)
+ , Quorum
+ , quorum
+ -- * Testing
+ , tests
+ ) where
+
+import Test.Framework (Test, testGroup)
+
+import Network.Paxos.Synod.Action
+import Network.Paxos.Synod.Messages
+import Network.Paxos.Synod.Types hiding (tests)
+
+import qualified Network.Paxos.Synod.Types
+import qualified Network.Paxos.Synod.Proposer
+import qualified Network.Paxos.Synod.Acceptor
+import qualified Network.Paxos.Synod.Learner
+
+-- | Tests for modules in "Network.Paxos.Synod"
+tests :: Test
+tests = testGroup "Network.Paxos.Synod" [
+ Network.Paxos.Synod.Types.tests
+ , Network.Paxos.Synod.Proposer.tests
+ , Network.Paxos.Synod.Acceptor.tests
+ , Network.Paxos.Synod.Learner.tests
+ ]
153 src/Network/Paxos/Synod/Acceptor.hs
@@ -0,0 +1,153 @@
+{- Paxos - Implementations of Paxos-related consensus algorithms
+ -
+ - Copyright (C) 2012 Nicolas Trangez
+ -
+ - This library is free software; you can redistribute it and/or
+ - modify it under the terms of the GNU Lesser General Public
+ - License as published by the Free Software Foundation; either
+ - version 2.1 of the License, or (at your option) any later version.
+ -
+ - This library is distributed in the hope that it will be useful,
+ - but WITHOUT ANY WARRANTY; without even the implied warranty of
+ - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ - Lesser General Public License for more details.
+ -
+ - You should have received a copy of the GNU Lesser General Public
+ - License along with this library; if not, write to the Free Software
+ - Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
+ - USA.
+ -}
+
+module Network.Paxos.Synod.Acceptor (
+ -- * Acceptor functionality
+ AcceptorState
+ , Action(..)
+ , initialize
+ -- ** Incoming message handlers
+ , handlePrepare
+ , handleAccept
+ -- * Testing
+ , tests
+ ) where
+
+import Data.Maybe (isNothing)
+
+import Test.Framework (Test, testGroup)
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+
+import Test.QuickCheck (Arbitrary, arbitrary)
+
+import Network.Paxos.Synod.Action
+import Network.Paxos.Synod.Types hiding (tests)
+import Network.Paxos.Synod.Messages
+
+-- | State of an Acceptor
+data AcceptorState nodeId value = AcceptorState { highestPromise :: Maybe (ProposalId nodeId)
+ , highestAccepted :: Maybe (AcceptedValue nodeId value)
+ }
+ deriving (Show, Eq)
+
+instance (Arbitrary nodeId, Arbitrary value) => Arbitrary (AcceptorState nodeId value) where
+ arbitrary = do
+ promised <- arbitrary
+ accepted <- case promised of
+ Nothing -> return Nothing
+ Just _ -> arbitrary
+ return $ AcceptorState promised accepted
+
+
+-- | Initial Acceptor state
+initialize :: AcceptorState nodeId value
+initialize = AcceptorState { highestPromise = Nothing
+ , highestAccepted = Nothing
+ }
+
+prop_initialize :: Bool
+prop_initialize = isNothing (highestPromise state0) && isNothing (highestAccepted state0)
+ where
+ state0 = initialize
+
+
+-- | Handle a single `Prepare' message received from a Proposer
+handlePrepare :: Ord nodeId
+ => AcceptorState nodeId value -- ^ Current state
+ -> nodeId -- ^ Identifier of the node from which the message was received
+ -> Prepare nodeId -- ^ Received message
+ -> (AcceptorState nodeId value, [Action nodeId value])
+handlePrepare state proposer (Prepare proposal) =
+ case highestPromise state of
+ Nothing -> (state', sendPromise)
+ Just promised -> case compare promised proposal of
+ LT -> (state', sendPromise)
+ EQ -> (state, []) -- Duplicate
+ GT -> (state, []) -- TODO Nack
+ where
+ state' = state { highestPromise = Just proposal }
+ sendPromise = [Send proposer $ MsgPromise $ Promise proposal (highestAccepted state')]
+
+prop_handlePrepare :: AcceptorState Int () -> Int -> Prepare Int -> Bool
+prop_handlePrepare state proposer msg@(Prepare proposalId) =
+ case highestPromise state of
+ Nothing -> (highestPromise state' == Just proposalId) &&
+ (actions == [Send proposer $ MsgPromise $ Promise proposalId Nothing])
+ Just promised -> (highestAccepted state' == highestAccepted state) &&
+ case compare promised proposalId of
+ LT -> (highestPromise state' == Just proposalId) &&
+ (actions == [Send proposer $ MsgPromise $ Promise proposalId (highestAccepted state)])
+ EQ -> state' == state && null actions
+ GT -> state' == state && null actions
+ where
+ (state', actions) = handlePrepare state proposer msg
+
+
+-- | Handle a single `Accept' message received from a Proposer
+handleAccept :: Ord nodeId
+ => AcceptorState nodeId value -- ^ Current state
+ -> Accept nodeId value -- ^ Received message
+ -> (AcceptorState nodeId value, [Action nodeId value])
+handleAccept state (Accept proposal value) =
+ case highestPromise state of
+ Nothing -> (state', [sendAccepted])
+ Just promised -> case compare promised proposal of
+ LT -> (state', [sendAccepted])
+ EQ -> case highestAccepted state of
+ Nothing -> (state', [sendAccepted])
+ Just (AcceptedValue p _) ->
+ if p == proposal
+ then (state, []) -- Duplicate
+ else (state', [sendAccepted])
+ GT -> (state, []) -- TODO Nack
+ where
+ state' = state { highestPromise = Just proposal
+ , highestAccepted = Just $ AcceptedValue proposal value
+ }
+ sendAccepted = Broadcast Learners $ MsgAccepted $ Accepted proposal value
+
+prop_handleAccept :: AcceptorState Int () -> Accept Int () -> Bool
+prop_handleAccept state msg@(Accept proposal value) =
+ case highestPromise state of
+ Nothing -> (state' == acceptedState) && (actions == [broadcastAccepted])
+ Just promised -> case compare promised proposal of
+ LT -> (state' == acceptedState) && (actions == [broadcastAccepted])
+ EQ -> case highestAccepted state of
+ Nothing -> (state' == acceptedState) && (actions == [broadcastAccepted])
+ Just (AcceptedValue p _) ->
+ if p == proposal
+ then (state' == state) && null actions
+ else (state' == acceptedState) && (actions == [broadcastAccepted])
+ GT -> (state' == state) && null actions
+ where
+ (state', actions) = handleAccept state msg
+ acceptedState = state { highestPromise = Just proposal
+ , highestAccepted = Just $ AcceptedValue proposal value
+ }
+ broadcastAccepted = Broadcast Learners $ MsgAccepted $ Accepted proposal value
+
+
+-- | Tests
+tests :: Test
+tests = testGroup "Network.Paxos.Synod.Acceptor" [
+ testProperty "initialize" prop_initialize
+ , testProperty "handlePrepare" prop_handlePrepare
+ , testProperty "handleAccept" prop_handleAccept
+ ]
41 src/Network/Paxos/Synod/Action.hs
@@ -0,0 +1,41 @@
+{- Paxos - Implementations of Paxos-related consensus algorithms
+ -
+ - Copyright (C) 2012 Nicolas Trangez
+ -
+ - This library is free software; you can redistribute it and/or
+ - modify it under the terms of the GNU Lesser General Public
+ - License as published by the Free Software Foundation; either
+ - version 2.1 of the License, or (at your option) any later version.
+ -
+ - This library is distributed in the hope that it will be useful,
+ - but WITHOUT ANY WARRANTY; without even the implied warranty of
+ - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ - Lesser General Public License for more details.
+ -
+ - You should have received a copy of the GNU Lesser General Public
+ - License along with this library; if not, write to the Free Software
+ - Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
+ - USA.
+ -}
+
+module Network.Paxos.Synod.Action (
+ BroadcastGroup(..)
+ , Action(..)
+ ) where
+
+import Network.Paxos.Synod.Messages
+
+-- | Broadcast group identifier
+data BroadcastGroup = Acceptors
+ | Learners
+ deriving (Show, Eq)
+
+
+-- | Actions which might need to be executed as the result of a state
+-- transition
+data Action nodeId value = Send nodeId (Message nodeId value)
+ -- ^ Send the given message to the given node
+ | Broadcast BroadcastGroup (Message nodeId value)
+ -- ^ Broadcast the given message to the given group
+ deriving (Show, Eq)
+
169 src/Network/Paxos/Synod/Learner.hs
@@ -0,0 +1,169 @@
+{- Paxos - Implementations of Paxos-related consensus algorithms
+ -
+ - Copyright (C) 2012 Nicolas Trangez
+ -
+ - This library is free software; you can redistribute it and/or
+ - modify it under the terms of the GNU Lesser General Public
+ - License as published by the Free Software Foundation; either
+ - version 2.1 of the License, or (at your option) any later version.
+ -
+ - This library is distributed in the hope that it will be useful,
+ - but WITHOUT ANY WARRANTY; without even the implied warranty of
+ - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ - Lesser General Public License for more details.
+ -
+ - You should have received a copy of the GNU Lesser General Public
+ - License along with this library; if not, write to the Free Software
+ - Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
+ - USA.
+ -}
+
+module Network.Paxos.Synod.Learner (
+ -- * Learner functionality
+ LearnerState
+ , initialize
+ -- ** Incoming message handlers
+ , handleAccepted
+ -- ** Result extraction
+ , getValue
+ -- * Testing
+ , tests
+ ) where
+
+import Control.Applicative
+
+import Data.Maybe (fromJust, isNothing)
+
+import Data.Map (Map)
+import qualified Data.Map as Map
+
+import Test.Framework (Test, testGroup)
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+
+import Test.QuickCheck (Arbitrary, arbitrary, oneof)
+
+import Network.Paxos.Synod.Types hiding (quorum, tests)
+import Network.Paxos.Synod.Messages
+
+-- | State of a Learner
+data LearnerState nodeId value = Learning { quorum :: Quorum
+ , highestAccepted :: Map nodeId (ProposalId nodeId)
+ , accepted :: Map (ProposalId nodeId) [nodeId]
+ }
+ | Decided value
+ deriving (Show, Eq)
+
+instance (Ord nodeId, Arbitrary nodeId, Arbitrary value) => Arbitrary (LearnerState nodeId value) where
+ arbitrary = oneof [learning, decided]
+ where
+ decided = Decided <$> arbitrary
+ learning = do
+ state0 <- initialize <$> arbitrary
+ mods <- arbitrary
+ let f (nodeId, msg) s = case handleAccepted s nodeId msg of
+ Decided _ -> s
+ s'@Learning{} -> s'
+ state = foldr f state0 mods
+ return state
+
+
+-- | Generate an initial Learner state
+initialize :: Quorum -- ^ Number of nodes which form a quorum
+ -> LearnerState nodeId value
+initialize quorum' = Learning { quorum = quorum'
+ , highestAccepted = Map.empty
+ , accepted = Map.empty
+ }
+
+prop_initialize :: Quorum -> Bool
+prop_initialize quorum' = and [ isNothing $ getValue state
+ , quorum state == quorum'
+ , Map.null $ highestAccepted state
+ , Map.null $ accepted state
+ ]
+ where
+ state = initialize quorum'
+
+
+-- | Handle a single Accepted message received from an Acceptor
+handleAccepted :: Ord nodeId
+ => LearnerState nodeId value -- ^ Current state
+ -> nodeId -- ^ Identifier of the node from which the message was received
+ -> Accepted nodeId value -- ^ Received message
+ -> LearnerState nodeId value
+handleAccepted state acceptor (Accepted proposalId value) =
+ case state of
+ Decided _ -> state
+ Learning{} ->
+ if acceptor `Map.member` highestAccepted state
+ then if highestProposalId >= proposalId
+ then state
+ else handleMember state
+ else handleNotMember state
+ where
+ Just highestProposalId = Map.lookup acceptor (highestAccepted state)
+
+ listToMaybe l
+ | null l = Nothing
+ | otherwise = Just l
+
+ handleMember s = handleNotMember $ s { accepted = Map.update (listToMaybe . filter (/= acceptor)) highestProposalId (accepted s) }
+
+ -- TODO This is plain ugly
+ handleNotMember s = check proposalId $ s { highestAccepted = Map.insert acceptor proposalId (highestAccepted s)
+ , accepted = Map.adjust ((:) acceptor) proposalId (accepted s `Map.union` Map.singleton proposalId [])
+ }
+
+ check p s =
+ if maybe 0 length (Map.lookup p (accepted s)) == fromIntegral (unQuorum (quorum s))
+ then Decided value
+ else s
+
+prop_handleAccepted1 :: LearnerState Int () -> Int -> Accepted Int () -> Bool
+prop_handleAccepted1 state acceptor msg@(Accepted proposalId _) =
+ isDecided || (fromJust (Map.lookup acceptor (highestAccepted state')) >= proposalId)
+ where
+ state' = handleAccepted state acceptor msg
+ isDecided = case state' of
+ Decided _ -> True
+ Learning{} -> False
+
+prop_handleAccepted2 :: LearnerState Int () -> Int -> Accepted Int () -> Bool
+prop_handleAccepted2 state acceptor msg
+ | isDecided = True
+ | otherwise = acceptor `elem` list
+ where
+ state' = handleAccepted state acceptor msg
+ isDecided = case state' of
+ Decided _ -> True
+ Learning{} -> False
+ Just p = Map.lookup acceptor (highestAccepted state')
+ Just list = Map.lookup p (accepted state')
+
+-- TODO Add property/test to check `Decided' is returned once quorum is
+-- reached
+
+
+-- | Extract the learned value from the Learner state, if any.
+--
+-- Once a value has been learned, handling more `Prepare' messages becomes
+-- a no-op.
+getValue :: LearnerState nodeId value -> Maybe value
+getValue state = case state of
+ Learning{} -> Nothing
+ Decided value -> Just value
+
+prop_getValue :: LearnerState Int Int -> Bool
+prop_getValue state = case state of
+ Decided value -> getValue state == Just value
+ Learning{} -> isNothing $ getValue state
+
+
+-- | Tests
+tests :: Test
+tests = testGroup "Network.Paxos.Synod.Learner" [
+ testProperty "initialize" prop_initialize
+ , testProperty "handleAccepted1" prop_handleAccepted1
+ , testProperty "handleAccepted2" prop_handleAccepted2
+ , testProperty "prop_getValue" prop_getValue
+ ]
72 src/Network/Paxos/Synod/Messages.hs
@@ -0,0 +1,72 @@
+{- Paxos - Implementations of Paxos-related consensus algorithms
+ -
+ - Copyright (C) 2012 Nicolas Trangez
+ -
+ - This library is free software; you can redistribute it and/or
+ - modify it under the terms of the GNU Lesser General Public
+ - License as published by the Free Software Foundation; either
+ - version 2.1 of the License, or (at your option) any later version.
+ -
+ - This library is distributed in the hope that it will be useful,
+ - but WITHOUT ANY WARRANTY; without even the implied warranty of
+ - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ - Lesser General Public License for more details.
+ -
+ - You should have received a copy of the GNU Lesser General Public
+ - License along with this library; if not, write to the Free Software
+ - Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
+ - USA.
+ -}
+
+module Network.Paxos.Synod.Messages (
+ Prepare(Prepare)
+ , Promise(Promise)
+ , Accept(Accept)
+ , Accepted(Accepted)
+ , Message(..)
+ ) where
+
+import Control.Applicative
+
+import Test.QuickCheck (Arbitrary, arbitrary)
+
+import Network.Paxos.Synod.Types
+
+data Prepare nodeId = Prepare (ProposalId nodeId)
+ deriving (Show, Eq)
+
+instance Arbitrary nodeId => Arbitrary (Prepare nodeId) where
+ arbitrary = Prepare <$> arbitrary
+
+
+data Promise nodeId value = Promise (ProposalId nodeId) (Maybe (AcceptedValue nodeId value))
+ deriving (Show, Eq)
+
+instance (Arbitrary nodeId, Arbitrary value) => Arbitrary (Promise nodeId value) where
+ arbitrary = Promise <$> arbitrary <*> arbitrary
+
+
+data Accept nodeId value = Accept (ProposalId nodeId) value
+ deriving (Show, Eq)
+
+instance (Arbitrary nodeId, Arbitrary value) => Arbitrary (Accept nodeId value) where
+ arbitrary = Accept <$> arbitrary <*> arbitrary
+
+
+data Accepted nodeId value = Accepted (ProposalId nodeId) value
+ deriving (Show, Eq)
+
+instance (Arbitrary nodeId, Arbitrary value) => Arbitrary (Accepted nodeId value) where
+ arbitrary = Accepted <$> arbitrary <*> arbitrary
+
+
+-- | Union type for all types of message which might flow across nodes
+data Message nodeId value = MsgPrepare (Prepare nodeId)
+ -- ^ A `Prepare' message, from Proposer to Acceptor
+ | MsgPromise (Promise nodeId value)
+ -- ^ A `Promise' message, from Acceptor to Proposer
+ | MsgAccept (Accept nodeId value)
+ -- ^ An `Accept' message, from Proposer to Acceptor
+ | MsgAccepted (Accepted nodeId value)
+ -- ^ An `Accepted' message, from Acceptor to Learner
+ deriving (Show, Eq)
145 src/Network/Paxos/Synod/Proposer.hs
@@ -0,0 +1,145 @@
+{- Paxos - Implementations of Paxos-related consensus algorithms
+ -
+ - Copyright (C) 2012 Nicolas Trangez
+ -
+ - This library is free software; you can redistribute it and/or
+ - modify it under the terms of the GNU Lesser General Public
+ - License as published by the Free Software Foundation; either
+ - version 2.1 of the License, or (at your option) any later version.
+ -
+ - This library is distributed in the hope that it will be useful,
+ - but WITHOUT ANY WARRANTY; without even the implied warranty of
+ - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ - Lesser General Public License for more details.
+ -
+ - You should have received a copy of the GNU Lesser General Public
+ - License along with this library; if not, write to the Free Software
+ - Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
+ - USA.
+ -}
+
+module Network.Paxos.Synod.Proposer (
+ -- * Proposer functionality
+ ProposerState
+ , Action(..)
+ , startRound
+ , handlePromise
+
+ -- * Re-exports of useful ProposalId functions
+ , ProposalId
+ , initialProposalId
+ , succProposalId
+
+ -- * Testing
+ , tests
+ ) where
+
+import Control.Applicative
+
+import Data.Maybe (isNothing)
+
+import Test.Framework (Test, testGroup)
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+
+import Test.QuickCheck (Arbitrary, arbitrary)
+
+import Network.Paxos.Synod.Action
+import Network.Paxos.Synod.Types hiding (quorum, tests)
+import Network.Paxos.Synod.Messages
+
+-- | State of a Proposer
+data ProposerState nodeId value = ProposerState { proposalId :: ProposalId nodeId
+ , quorum :: Quorum
+ , value :: value
+ , acceptors :: [nodeId]
+ , highestAccepted :: Maybe (AcceptedValue nodeId value)
+ }
+ deriving (Show, Eq)
+
+instance (Arbitrary nodeId, Arbitrary value) => Arbitrary (ProposerState nodeId value) where
+ arbitrary = ProposerState <$> arbitrary <*> arbitrary <*> arbitrary <*> arbitrary <*> arbitrary
+
+
+-- | Start a single round using given quorum, `ProposalId' and value to propose
+startRound :: Quorum -- ^ Quorum size
+ -> ProposalId nodeId -- ^ `ProposalId' to use
+ -> value -- ^ Value to propose
+ -> (ProposerState nodeId value, [Action nodeId value])
+startRound quorum' proposalId' value' = (state, [msg])
+ where
+ state = ProposerState { proposalId = proposalId'
+ , quorum = quorum'
+ , value = value'
+ , acceptors = []
+ , highestAccepted = Nothing
+ }
+ msg = Broadcast Acceptors $ MsgPrepare $ Prepare proposalId'
+
+prop_startRound1 :: Quorum -> ProposalId Int -> () -> Bool
+prop_startRound1 q p v = and [ proposalId s == p
+ , quorum s == q
+ , value s == v
+ , null $ acceptors s
+ , isNothing $ highestAccepted s
+ ]
+ where
+ (s, _) = startRound q p v
+
+prop_startRound2 :: Quorum -> ProposalId Int -> () -> Bool
+prop_startRound2 q p v = actions == [Broadcast Acceptors $ MsgPrepare $ Prepare p]
+ where
+ (_, actions) = startRound q p v
+
+
+-- | Handle a single `Promise' message received from an Acceptor
+handlePromise :: Ord nodeId => ProposerState nodeId value -- ^ Current state
+ -> nodeId -- ^ Identifier of the node from which the message was received
+ -> Promise nodeId value -- ^ Received message
+ -> (ProposerState nodeId value, [Action nodeId value])
+handlePromise state acceptor (Promise proposalId' highestAccepted')
+ | proposalId' < proposalId state = (state, [])
+ | proposalId' > proposalId state = (state, []) -- TODO Give up and start new round?
+ | otherwise =
+ if acceptor `elem` acceptors state
+ then (state, [])
+ else (state', msgs)
+ where
+ state' = state { acceptors = acceptor : acceptors state
+ , highestAccepted = selectedAccepted
+ }
+ selectedAccepted = case highestAccepted state of
+ Nothing -> highestAccepted'
+ Just v -> case highestAccepted' of
+ Nothing -> Just v
+ Just v' -> Just $ max v v'
+ msgs = if length (acceptors state') /= fromIntegral (unQuorum $ quorum state')
+ then []
+ else [Broadcast Acceptors $ MsgAccept $ Accept (proposalId state') (value state')]
+
+prop_handlePromise :: ProposerState Int ()
+ -> Int
+ -> Promise Int ()
+ -> Bool
+prop_handlePromise state acceptor p@(Promise proposalId' highestAccepted')
+ | proposalId' /= proposalId state = result == (state, [])
+ | otherwise =
+ if acceptor `elem` acceptors state
+ then result == (state, [])
+ else and [ acceptor `elem` acceptors state'
+ , length (acceptors state') == length (acceptors state) + 1
+ , highestAccepted state' == max (highestAccepted state) highestAccepted'
+ , proposalId state' == proposalId state
+ , (length (acceptors state') /= fromIntegral (unQuorum $ quorum state')) ||
+ (actions == [Broadcast Acceptors $ MsgAccept $ Accept (proposalId state') (value state')])
+ ]
+ where
+ result@(state', actions) = handlePromise state acceptor p
+
+
+-- | Tests
+tests :: Test
+tests = testGroup "Network.Paxos.Synod.Proposer" [
+ testProperty "startRound1" prop_startRound1
+ , testProperty "startRound2" prop_startRound2
+ , testProperty "handlePromise" prop_handlePromise
+ ]
162 src/Network/Paxos/Synod/Types.hs
@@ -0,0 +1,162 @@
+{- Paxos - Implementations of Paxos-related consensus algorithms
+ -
+ - Copyright (C) 2012 Nicolas Trangez
+ -
+ - This library is free software; you can redistribute it and/or
+ - modify it under the terms of the GNU Lesser General Public
+ - License as published by the Free Software Foundation; either
+ - version 2.1 of the License, or (at your option) any later version.
+ -
+ - This library is distributed in the hope that it will be useful,
+ - but WITHOUT ANY WARRANTY; without even the implied warranty of
+ - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ - Lesser General Public License for more details.
+ -
+ - You should have received a copy of the GNU Lesser General Public
+ - License along with this library; if not, write to the Free Software
+ - Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
+ - USA.
+ -}
+
+module Network.Paxos.Synod.Types (
+ -- * Proposal identifier handling
+ ProposalId
+ , initialProposalId
+ , succProposalId
+ , bumpProposalId
+
+ -- * Utilities
+ , Quorum(unQuorum)
+ , quorum
+ , AcceptedValue(..)
+
+ -- * Testing
+ , tests
+ ) where
+
+import Control.Applicative ((<$>), (<*>))
+
+import Data.Word (Word, Word64)
+
+import Test.Framework (Test, testGroup)
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+
+import Test.QuickCheck (Arbitrary, arbitrary)
+
+-- | Representation of a proposal identifier
+data ProposalId nodeId = ProposalId {-# UNPACK #-} !Word64 nodeId
+ deriving (Show, Eq)
+
+-- Note: even though the following instance should be exactly the one
+-- derived using `deriving(Ord)', I prefer to provide an explicit
+-- implementation
+instance Ord nodeId => Ord (ProposalId nodeId) where
+ compare (ProposalId i1 n1) (ProposalId i2 n2)
+ | i1 /= i2 = compare i1 i2
+ | otherwise = compare n1 n2
+
+instance Arbitrary a => Arbitrary (ProposalId a) where
+ arbitrary = ProposalId <$> arbitrary <*> arbitrary
+
+prop_ProposalId_Ord :: ProposalId Int -> ProposalId Int -> Bool
+prop_ProposalId_Ord p1@(ProposalId i1 n1) p2@(ProposalId i2 n2)
+ | i1 > i2 = p1 > p2
+ | i1 < i2 = p1 < p2
+ | otherwise = compare p1 p2 == compare n1 n2
+
+-- | Generate the initial (lowest) 'ProposalId' the given node will ever
+-- use
+initialProposalId :: nodeId -- ^ Identifier of the node which will send the proposal
+ -> ProposalId nodeId
+initialProposalId = ProposalId 1
+
+-- | Calculate a new 'ProposalId' which will be greater than the given one,
+-- retaining the node identifier
+succProposalId :: Ord nodeId
+ => ProposalId nodeId -- ^ Proposal to increment
+ -> ProposalId nodeId
+succProposalId p = bumpProposalId p p
+
+prop_succProposalId1 :: ProposalId Int -> Bool
+prop_succProposalId1 p = succProposalId p > p
+
+prop_succProposalId2 :: ProposalId Int -> Bool
+prop_succProposalId2 p = succProposalId p < succProposalId (succProposalId p)
+
+-- | Bump a proposal so it becomes greater than another one, e.g. to
+-- restart a round with a higher 'ProposalId' based on `Nack' messages
+bumpProposalId :: Ord nodeId
+ => ProposalId nodeId -- ^ Proposal to bump
+ -> ProposalId nodeId -- ^ Proposal to exceed
+ -> ProposalId nodeId
+bumpProposalId p1@(ProposalId _ nodeId) p2@(ProposalId i _)
+ | p1 > p2 = p1
+ | otherwise = ProposalId (i + 1) nodeId
+
+prop_bumpProposalId1 :: ProposalId Int -> ProposalId Int -> Bool
+prop_bumpProposalId1 p1 p2 = bumpProposalId p1 p2 > p2
+
+prop_bumpProposalId2 :: ProposalId Int -> ProposalId Int -> Bool
+prop_bumpProposalId2 p1 p2 = p2' > p1'
+ where
+ p1' = bumpProposalId p1 p2
+ p2' = bumpProposalId p2 p1'
+
+-- | Quorum number
+newtype Quorum = Quorum { unQuorum :: Word }
+ deriving (Show, Eq, Ord)
+
+instance Arbitrary Quorum where
+ arbitrary = Quorum <$> arbitrary
+
+-- | Smart constructor for `Quorum' values
+quorum :: (Integral a, Ord a) => a -> Quorum
+quorum q
+ | q < 0 = error "quorum: Negative value"
+ | toInteger q > toInteger (maxBound :: Word) = error "quorum: Overflow"
+ | otherwise = Quorum $ fromIntegral q
+
+
+-- | Representation of something accepted by an acceptor
+data AcceptedValue nodeId value = AcceptedValue { acceptedProposalId :: ProposalId nodeId
+ , acceptedValue :: value
+ }
+ deriving (Show)
+
+-- Explicit Eq and Ord instances so there's no (unnecessary) Eq or Ord
+-- constraint on `value', since these should always be equal if the
+-- corresponding `ProposalId' is equal, and useless for comparison
+instance Eq nodeId => Eq (AcceptedValue nodeId value) where
+ a == b = acceptedProposalId a == acceptedProposalId b
+
+instance Ord nodeId => Ord (AcceptedValue nodeId value) where
+ compare a b = compare (acceptedProposalId a) (acceptedProposalId b)
+
+instance (Arbitrary nodeId, Arbitrary value) => Arbitrary (AcceptedValue nodeId value) where
+ arbitrary = AcceptedValue <$> arbitrary <*> arbitrary
+
+
+prop_AcceptedValue_Eq :: AcceptedValue Int () -> AcceptedValue Int () -> Bool
+prop_AcceptedValue_Eq a1 a2 =
+ (a1 == a2) == (acceptedProposalId a1 == acceptedProposalId a2)
+
+prop_AcceptedValue_Ord :: AcceptedValue Int () -> AcceptedValue Int () -> Bool
+prop_AcceptedValue_Ord a1 a2 =
+ compare a1 a2 == compare (acceptedProposalId a1) (acceptedProposalId a2)
+
+
+-- | Tests
+tests :: Test
+tests = testGroup "Network.Paxos.Synod.Types" [
+ -- ProposalId
+ testProperty "ProposalId Ord" prop_ProposalId_Ord
+ -- succProposalId
+ , testProperty "succProposalId1" prop_succProposalId1
+ , testProperty "succProposalId2" prop_succProposalId2
+ -- bumpProposalId
+ , testProperty "bumpProposalId1" prop_bumpProposalId1
+ , testProperty "bumpProposalId2" prop_bumpProposalId2
+ -- AcceptedValue
+ , testProperty "AcceptedValue Eq" prop_AcceptedValue_Eq
+ , testProperty "AcceptedValue Ord" prop_AcceptedValue_Ord
+ ]

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