F# in social gaming (CodeMash 15)

1. F# in Social GamingF# in Social Gaming Yan Cui (@theburningmonk)

2. agenda

3. Hi, my name is Yan Cui.

4. 1MILLION USERS ACTIVE DAILY

5. 250MILLION DAY PER REQUEST

6. why F#?

7. time to market

8. correctness

9. efficient

10. tame complexity

11. Implementing a slots engine

12. Collectables Wager Size Special Symbol Avg Wager Size Web Server call

13. • Line Win! – X number of matching symbols on adjacent columns! – Positions have to be a ‘line’! – Wild symbols substitute for other symbols! ! • Scatter Win! – X number of matching symbols anywhere! – Triggers bonus game

14. What symbols should land?! Any special symbol wins?! Did the player win anything?

15. What the player’s new average wager?

16. Should the player receive collectables?

17. type Symbol = Standard! of string! ! ! ! | Wild

18. type Symbol = Standard! of string! ! ! ! | Wild e.g.! Standard “hat”! ! Standard “shoe”! ! Standard “bonus”! ! …

19. type Symbol = Standard! of string! ! ! ! | Wild i.e.! Wild

20. ! ! ! type Win = LineWin of int * Symbol * int! ! | ScatterWin of Symbol * int

21. ! ! ! type Win = LineWin of int * Symbol * int! ! | ScatterWin of Symbol * int e.g.! LineWin (5, Standard “shoe”, 4)

22. ! ! ! type Win = LineWin of int * Symbol * int! ! | ScatterWin of Symbol * int e.g.! ScatterWin (Standard “bonus”, 3)

23. type LineNum = int! type Count! = int! ! type Win = LineWin of LineNum * Symbol * Count! ! | ScatterWin of Symbol * Count

24. type LineNum = int! type Count! = int! ! type Win = LineWin of LineNum * Symbol * Count! ! | ScatterWin of Symbol * Count e.g.! LineWin (5, Standard “shoe”, 4)

25. type LineNum = int! type Count! = int! ! type Win = LineWin of LineNum * Symbol * Count! ! | ScatterWin of Symbol * Count e.g.! ScatterWin (Standard “bonus”, 3)

26. make invalid states unrepresentable

27. NASA orbiter crashed because one engineer accidentally used miles instead of kilometres

28. you’re never too smart to make mistakes

29. [<Measure>]! type Pence e.g.! 42<Pence>! ! 153<Pence>! ! …

30. 10<Meter> / 2<Second> ! = 5<Meter/Second>! 10<Meter> * 2<Second> ! = 20<Meter Second> ! 10<Meter> + 10<Meter> ! = 20<Meter>! 10<Meter> * 10! ! ! = 100<Meter>! 10<Meter> * 10<Meter> ! = 100<Meter2>! 10<Meter> + 2<Second> ! // error! 10<Meter> + 2 ! ! ! // error

31. 10<Meter> / 2<Second> ! = 5<Meter/Second>! 10<Meter> * 2<Second> ! = 20<Meter Second> ! 10<Meter> + 10<Meter> ! = 20<Meter>! 10<Meter> * 10! ! ! = 100<Meter>! 10<Meter> * 10<Meter> ! = 100<Meter2>! 10<Meter> + 2<Second> ! // error! 10<Meter> + 2 ! ! ! // error

32. type Wager = int64<Pence>! type Multiplier = int! ! type Payout = Coins! of Wager! ! ! | MultipliedCoins of Multiplier * Wager! ! ! | Multi! of Payout list! ! ! | BonusGame

35. type State = ! {! AvgWager! : Wager! SpecialSymbol : Symbol! Collectables : Map<Collectable, Count>! }

36. New avg wager Got a Collectable! A pay line win!

37. Betting small reduces avg wager! Bonus Game!

42. [<Measure>]! type Position! ! type MonopolyBoard =! {! Spaces : MonopolyBoardSpace [ ]! }! member this.Item with ! get (pos : int<Position>) =! this.Spaces.[int pos]

43. [<Measure>]! type Position! ! type MonopolyBoard =! {! Spaces : MonopolyBoardSpace [ ]! }! member this.Item with ! get (pos : int<Position>) = ! this.Spaces.[int pos]

44. And a pay line win! Coin size brought over from main game Houses = multiplier on wins GAME OVER Collected in the bonus game. Gives player extra ‘lives’.

45. type BonusGameState =! {! Board ! : MonopolyBoard! Position ! : int<Position>! Lives ! : int<Life>! Doubles! : int<Double>! CoinSize! : Wager! TotalWin! : Wager! }

46. Coin size brought over from main game

48. And a pay line win! Houses = multiplier on wins

50. Collected in the bonus game. Gives player extra ‘lives’.

52. 0<Position>

53. let jail = 6<Position>

54. let rec move newPos state =! match state.Board.[newPos] with! …! | GotoJail when state.Lives = 0<Life> -> ! ! move jail state |> gameOver! | GotoJail ! ! -> move jail state! …

63. let rec move newPos state =! match state.Board.[newPos] with! …! | RailRoad true ! -> awardRailRoadMultiplier state! | Property n when n > 0 -> awardPropertyMultiplier n state! | ElectricityCompany true! | WaterCompany true -> awardUtilityMultiplier state! …

64. let rec move newPos state =! match state.Board.[newPos] with! …! | CommunityChest! -> playCommunityChestCard state! | Chance ! ! -> playChanceCard state! …

68. Recap

69. lightweight syntax to create types and hierarchies

70. great for domain modelling

71. make invalid states unrepresentable

72. clear, concise way to handle branching

73. better correctness

74. order of magnitude increase in productivity

75. Stateful Server

76. player states are big

77. Stateless Server DatabaseClient

78. 1:1 read-write ratio

79. stateless = ! Inefficient & Expensive

80. ServerClient Session 1 Session 2

81. ServerClient Database

82. Elastic Load Balancer S3 Auto scaling Group Server A Server B ... EC2 CloudFront Stateful Server

83. The Actor Model An actor is the fundamental unit of computation which embodies the 3 things! • Processing! • Storage! • Communication! that are essential to computation.! ! -Carl Hewitt* * http://bit.ly/HoNHbG

84. The Actor Model • Everything is an actor! • An actor has a mailbox! • When an actor receives a message it can:! – Create new actors! – Send messages to actors! – Designate how to handle the next message

85. Stateful Server • Gatekeeper! – Manages the local list of active workers! – Spawns new workers! ! • Worker! – Manages the states for a player! – Optimistic locking! – Persist state after period of inactivity

86. Stateful Server Game Server Player A Player B S3 Worker C Worker B Gatekeeper RequestHandlers Asynchronous

87. Stateful Server Game Server Worker C Worker B Gatekeeper Worker A ok RequestHandlers Player A Player B Asynchronous S3

88. Stateful Server Game Server S3 Worker C Worker B Gatekeeper Worker A RequestHandlers Player A Player B Asynchronous

89. Stateful Server Game Server S3 Worker C Gatekeeper Worker A RequestHandlers Player A Player B Asynchronous

90. Stateful Server Game Server Worker C Worker A Gatekeeper error RequestHandlers Player A Player B S3 Asynchronous

91. type Agent<‘T> = MailboxProcessor<‘T>! ! ! !

92. type Agent<‘T> = MailboxProcessor<‘T>! ! type Message = ! | Get of AsyncReplyChannel<…>! | Put of State * Version * AsyncReplyChannel<…>

93. type Agent<‘T> = MailboxProcessor<‘T>! ! type Message = ! | Get of AsyncReplyChannel<…>! | Put of State * Version * AsyncReplyChannel<…>

94. type Result<‘T> =! | Success! of ’T! | Failure! of Exception! ! ! !

95. type Result<‘T> =! | Success! of ’T! | Failure! of Exception! ! type GetResult = Result<State * Version>! type PutResult = Result<unit>!

96. type Agent<‘T> = MailboxProcessor<‘T>! ! type Message = ! | Get of AsyncReplyChannel<GetResult>! | Put of State * Version * AsyncReplyChannel<PutResult>

97. type Agent<‘T> = MailboxProcessor<‘T>! ! type Message = ! | Get of AsyncReplyChannel<GetResult>! | Put of State * Version * AsyncReplyChannel<PutResult>

98. type Worker (playerId) =! let agent = Agent<Message>.Start(fun inbox ->! let state = getCurrentState playerId! ! let rec workingState (state, version) = ! async { … }! and closedState () =! async { … }! ! workingState (state, 1))

103. let rec workingState (state, version) = ! async { ! let! msg = inbox.TryReceive(60000)! match msg with! | None -> ! do! persist state! return! closedState()! …! }!

106. non-blocking I/O

109. let rec workingState (state, version) = ! async { ! let! msg = inbox.TryReceive(60000)! match msg with! …! | Some(Get(reply)) ->! reply.Reply <| Success(state, version)! return! workingState(state, version)! …! }!

110. let rec workingState (state, version) = ! async { ! let! msg = inbox.TryReceive(60000)! match msg with! …! | Some(Put(newState, v, reply)) when version = v ->! reply.Reply <| Success()! return! workingState(newState, version+1)! …! }

111. let rec workingState (state, version) = ! async { ! let! msg = inbox.TryReceive(60000)! match msg with! …! | Some(Put(_, v, reply)) ->! reply.Reply <| Failure(VersionMismatch(version, v))! return! workingState(state, version)! }

112. let rec workingState (state, version) = ! async { ! let! msg = inbox.TryReceive(60000)! match msg with! | None ! ! ! ! ! ! ! -> …! | Some(Get(reply)) ! ! ! ! ! -> …! | Some(Put(newState, v, reply)) when version = v ! -> …! | Some(Put(_, v, reply)) ! ! ! ! -> …! }

113. and closedState () = ! async { ! let! msg = inbox.Receive()! match msg with! | Get(reply) ->! reply.Reply <| Failure(WorkerStopped)! return! closedState()! | Put(_, _, reply) ->! reply.Reply <| Failure(WorkerStopped)! return! closedState()! }

114. and closedState () = ! async { ! let! msg = inbox.Receive()! match msg with! | Get(reply) ->! reply.Reply <| Failure(WorkerStopped)! return! closedState()! | Put(_, _, reply) ->! reply.Reply <| Failure(WorkerStopped)! return! closedState()! }

115. 5x efficient improvement

116. 60% latency drop

117. no databases

118. need to ensure server affinity

119. need to balance load

120. need to avoid hotspots

121. • Persist player state after short inactivity! • Move player to another server after persistence

122. need to gracefully scale down

123. Recap

124. Agents! • no locks! • async message passing! !

125. Agents! • no locks! • async message passing! • self-contained! • easy to reason with

126. Agents! • low level! • exceptions kills agents! • primitive error monitoring! • no supervision! • no distribution

127. MS Orleans Cricket akka.Net

128. Async Workflow! • non-blocking I/O! • no callbacks

129. Pattern Matching! • clear & concise

130. Replacing a large class hierarchy

131. Caught a Gnome

132. EXP Item Gold Quest Progress Caught a Gnome

133. Level Up Quest Progress EXP Item Gold Caught a Gnome Quest Complete

134. Level Up Quest Progress EXP Item Gold Caught a Gnome New Quest Quest Complete

135. Quest Progress EXP Item Gold Caught a Gnome Quest Complete New Quest Level Up

136. Quest Progress New Quest Achievement Progress EXP Item Gold Quest Complete Level Up Caught a Gnome

137. Level Up Quest Progress EXP Item Gold Caught a Gnome Quest Complete New Quest Achievement Progress Achievement Complete

138. Level Up Quest Progress EXP Item Gold Caught a Gnome Quest Complete New Quest Achievement Progress Achievement Complete

139. 100+ actions

140. triggered by different abstraction layers

141. non-functional requirements

142. message-broker pattern

143. Caught Gnome Trapping Queue Levelling Quests Achievements Analytics Partner Reporting

144. Caught Gnome Trapping Queue Levelling Quests Achievements Analytics Partner Reporting Ignore Process Process Process Process Ignore

145. Caught Gnome Trapping Queue Levelling Quests Achievements Analytics Partner Reporting EXP Item Gold

146. Caught Gnome Trapping Queue Levelling Quests Achievements Analytics Partner Reporting EXP Item Gold

147. Caught Gnome Trapping Queue Levelling Quests Achievements Analytics Partner Reporting EXP Item Gold Process Ignore Ignore Ignore Process Ignore

148. Caught Gnome Trapping Queue Levelling Quests Achievements Analytics Partner Reporting EXP Item Gold Level Up

149. Caught Gnome Trapping Queue Levelling Quests Achievements Analytics Partner Reporting EXP Item Gold Level Up

150. need lots of facts

152. type Reward =! | GotExp! ! of Exp! | GotGold! ! of Gold! | GotItem! ! of Item * Count! ! type StateChange =! | LevelUp! ! of OldLevel * NewLevel! …

153. type Fact =! | StateChange! of StateChange! | Reward! ! of Reward! | Trapping! ! of Trapping! | Fishing! ! of Fishing! …

154. let process fact =! match fact with! | StateChange(stateChange)! -> …! | Reward(reward)! ! ! -> …! | Trapping(trapping)! ! -> …! …

155. C# interop

156. …! var fact = Fact.NewStateChange(! ! StateChange.NewLevelUp(oldLvl, newLvl));! …

157. type IFact = interface end! ! type Reward =! | GotExp! ! of Exp! | GotGold! ! of Gold! | GotItem! ! of Item * Count! interface IFact

158. type IFact = interface end! ! type Reward =! | GotExp! ! of Exp! | GotGold! ! of Gold! | GotItem! ! of Item * Count! interface IFact

161. simple

162. flexible

163. extensible

164. saver

165. April 2015

166. Fri 8.30am, Salon H @theburningmonk / theburningmonk.com

167. Fri 8.30am, Salon H Fri 2.45pm, Guava + Tamarind @theburningmonk / theburningmonk.com