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Finite State Machines - Why the fear?
The document discusses Erlang's capabilities for handling concurrency and state management using finite state machines (FSMs) in telecommunications systems. It highlights metrics for performance measurement, including phone call handling and API requests, while emphasizing the importance of error handling and system stability. The content also stresses the significance of encapsulation and state transitions in building efficient systems.
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Finite State Machines - Why the fear?
- 1. { Erlang and gen_fsm @dieswaytoofast (V.P.Ubiquiti Networks)
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- 6. ď Phone Callsper Second The Metrics
- 7. ď Phone Callsper Second The Metrics x 1000
- 8. ď Simultaneous PhoneCalls The Metrics
- 9. ď Simultaneous PhoneCalls The Metrics x 10,000
- 10. ď HTTP APIrequests The Metrics
- 11. ď HTTP APIrequests The Metrics x â
- 12.
- 13. ď Voice Response CallHandling init Setup Call Get Caller Name Play Transfer Message Got Caller Name Dial
- 14. ď Call Routing CallHandling dial_in Check Blacklist get_endpoint conference Play Error Hangupauto_attendant dial_in_fml conference
- 15. init Check node Check Blacklist Cancelled BlacklistedNext Endpoint Collections Unknown Move node Auto Attendant FML Voicemail FaxConference
- 16. ď Self-hosted (kinda) Betthe farm moment
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- 19. ď Concurrency The BigSix From http://www.erlang.org/download/armstrong_thesis_2003.pdf
- 20. ď Concurrency ď Errorencapsulation The Big Six From http://www.erlang.org/download/armstrong_thesis_2003.pdf
- 21. ď Concurrency ď Errorencapsulation ď Fault detection The Big Six From http://www.erlang.org/download/armstrong_thesis_2003.pdf
- 22. ď Concurrency ď Errorencapsulation ď Fault detection ď Fault identification The Big Six From http://www.erlang.org/download/armstrong_thesis_2003.pdf
- 23. ď Concurrency ď Errorencapsulation ď Fault detection ď Fault identification ď Code upgrade The Big Six From http://www.erlang.org/download/armstrong_thesis_2003.pdf
- 24. ď Concurrency ď Errorencapsulation ď Fault detection ď Fault identification ď Code upgrade ď Stable Storage The Big Six From http://www.erlang.org/download/armstrong_thesis_2003.pdf
- 25. Erlang Concurrency Hell My BlueHeaven My Blue Heaven
- 26. Erlang Concurrency Hell My BlueHeaven Deep Problems My Blue Heaven Deep Problems
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- 29. ď gen_server ď gen_tcp ďgen_event Behaviours
- 30. ď gen_server ď gen_tcp ďgen_event ď gen_fsm Behaviours
- 31. ď gen_server ď gen_tcp ďgen_event ď gen_fsm ď ⌠Behaviours
- 32. ď gen_server ď gen_tcp ďgen_event ď gen_fsm ď ⌠Behaviours
- 33. ď A Systemhas States Finite State Machines
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- 35. ď A Systemhas States ď States transition Finite State Machines
- 36.
- 37. ď A Systemhas States ď States transition ď Transitions are Atomic Finite State Machines
- 38.
- 39. ď A Systemhas States ď States transition ď Transitions are Atomic ď Events at Entry and Exit Finite State Machines
- 40. asleepStart out of bed Riiiiiiiiing BrushTeeth Coffee!!
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- 43. asleepStart out of bed Riiiiiiiiing BrushTeeth Coffee!!
- 44. asleepStart out of bed Riiiiiiiiing BrushTeeth Coffee!!
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- 46. asleepStart out of bed Riiiiiiiiing BrushTeeth Coffee!! HUH?
- 48. asleepStart out of bed Riiiiiiiiing BrushTeeth Coffee!!
- 49. asleepStart out of bed Riiiiiiiiing BrushTeeth Coffee!! W 00t!
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- 72. ď Everything isan FSM Finite State Machines
- 73. ď Everything isan FSM Finite State Machines COM PLEXITY?
- 74. ď Everything isan FSM Finite State Machines ENCAPSULATION!
- 75. ď Voice Response FiniteState Machines init Setup Call Get Caller Name Play Transfer Message Got Caller Name Dial
- 76. ď Voice Response FiniteState Machines init Setup Call Get Caller Name Play Transfer Message Got Caller Name Dial
- 77. ď Voice Response FiniteState Machines init Setup Call Get Caller Name Play Transfer Message Got Caller Name Dial ENCAPSULATION!
- 78. Encapsulation Concurrency Hell My BlueHeaven Deep Problems My Blue Heaven Deep Problems
- 79. ď Call Routing FiniteState Machines dial_in Check Blacklist get_endpoint conference Play Error Hangupauto_attendant dial_in_fml conference
- 80. init Check node Check Blacklist Cancelled BlacklistedNext Endpoint Collections Unknown Move node Auto Attendant FML Voicemail FaxConference
- 81. ď Templates areyour friend ď So are BIG sheets of paper ď Think âReal Worldâ The Bottom Line
Editor's Notes
- #3Â So, I started a phone company. It was a great thing. Phones make people happy, right?
- #4Â Yeah. Kids. Donât do this at home. Donât start a phone company.
- #5Â But I did. Hosted phone services for SMBs. Vonage for small businesses. In the cloud. Awesome
- #8Â 3 orders of magnitude
- #10Â 4 orders of magnitude
- #12Â Infinity!
- #13Â Houston â we have a problem
- #14Â Consider the simplest case of handling a call
- #15Â It actually gets a lot more complex
- #16Â And eventually, a *lot* more complex
- #17Â To put it differently,It was a âbet the farmâ moment
- #18Â And it basically involved a lot of beer
- #19Â And we rewrote the whole damn thing in Erlang. WhyErlang? Well, Fault Tolerance, basicallyAnd oh, Iâm not putting Kirk up there. Thatâs too obvious.
- #20Â The Six Essential Characteristics of a Fault Tolerant System
- #21Â The Six Essential Characteristics of a Fault Tolerant System
- #22Â The Six Essential Characteristics of a Fault Tolerant System
- #23Â The Six Essential Characteristics of a Fault Tolerant System
- #24Â The Six Essential Characteristics of a Fault Tolerant System
- #25Â The Six Essential Characteristics of a Fault Tolerant System
- #26Â âDistributedâ problems mean you spend a huge chunk of your time dealing with theadminstrivia of distribution.With erlang you get that for free!
- #27Â Ok, not really true. You still have to deal with âdeep problemsâ (hard core parallelization issues, etc.)But youâd have to deal with that anyhow!
- #28Â Implement the server part of a client/server relationship
- #29Â Talk to tcp over sockets
- #30Â Event handling
- #31Â Finite state machines
- #32Â And a bunch more (gen_udp, gen_utp!, etc.)
- #33Â But, weâre talking about Finite State Machines
- #34Â Lets talk about FSMs
- #42Â Putting this into practice, here is some code
- #43Â A system has states
- #44Â When certain events show up
- #45Â You do something
- #46Â And transition to the next state
- #47Â Wait, WHUT? Where did the âeventsâ come from?
- #48Â Iâm glad you asked ď more code
- #49Â And thusly an event is sent
- #50Â Voila, an ErlangFSM
- #51Â 2.0 is anightmare; Stick w/ 1.0
- #52Â A system has states
- #53Â Events and transitions
- #54Â The code
- #55Â The states
- #57Â When you receive an event
- #58Â try to do something
- #59Â If it works go to the next state
- #61Â If it fails, go to a differen state
- #62Â Thusly
- #63Â And now for the events
- #68Â But wait! What if you walk out partway?
- #69Â So, a wee bit triclyhere -
- #70Â We have a timeout
- #71Â And it tells you where to go after the timeout
- #72Â And, youâre done.
- #73Â Lets look at this as a âreal worldâ thingy
- #74Â But, you say, BUT, what about the complexity of dealing with FSMs? Theyâre big! And unweildy!
- #75Â Nah. They arenât. Not in Erlang
- #76Â Remember this? It was a PITA? Actually, a small part of a PITA?
- #77Â But each one is tightly encapsulated, and clean.Itâs the Erlang Way
- #78Â But each one is tightly encapsulated, and clean.Itâs the Erlang Way
- #79Â My fanciful slides are actually real. This actually happens.
- #80Â And itâs the same for everything else I showed. FSMs of FSMs.
- #81Â An FSM of FSMs of FSMsBuilding these out âcorrectlyâ, in real time, is (was!) trivial
- #82Â âReal Worldâ ď Business Rules can help. (VM,syncrhonziation)