Life of an Erlang process

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Life of an Erlang Process @robertoaloi

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Let’s talk about Erlang

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I won’t talk about the Erlang syntax.

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Syntax is Irrelevant Programming Language is Not When you’ll look at the syntax, it’ll be too late.

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ERLANG HAS BEEN DESIGNED TO HELP YOU WRITING SYSTEMS SCALABLE

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ERLANG HAS BEEN DESIGNED TO HELP YOU WRITING SYSTEMS FAULT-TOLERANT

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ERLANG HAS BEEN DESIGNED TO HELP YOU WRITING SYSTEMS HIGHLY AVAILABLE

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ERLANG HAS BEEN DESIGNED TO HELP YOU WRITING SYSTEMS MASSIVELY CONCURRENT

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ERLANG HAS BEEN DESIGNED TO HELP YOU WRITING SYSTEMS DISTRIBUTED

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ERLANG HAS BEEN DESIGNED TO HELP YOU WRITING SYSTEMS SOFT REAL-TIME

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The Erlang Rationale Users as Processes Scalable System Tons of Users Tons of Processes

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Think Erlang Think Processes

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Tons of them.

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DEALING WITH TONS OF PROCESSES

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Cheap to create Cheap to context switch OS processes out of discussion Use lightweight processes Built-in distribution to horizontally scale

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SHARED MEMORY (or lack thereof)

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Shared memory can leave the system in an inconsistent state after a restart or crash. Avoid it.

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FAIL FAST

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Faults are everywhere, you cannot prevent them. Report failure and die.

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Processes are good. Can you show me one?

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<0.42.0>

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How are processes made? This is a little embarrassing, but… Ahem… I’m not sure I understand everything of it… I’ve heard rumours, still… Do you, do you mind if I ask you…

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spawn(math, fact, [5]) math:fact(5) Pid2 Pid1

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MESSAGE PASSING

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Pid2 Pid1 Pid2 ! {self(), Msg} {Pid1, Msg} receive {From, start} -> … {From, stop} -> … end Send Receive

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THE PROCESS SKELETON

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start(Args) -> spawn(server, init, [Args]) init(Args) -> State = do_init(Args), loop(State). loop(State) ->  receive  {handle, Msg} ->   NewState = handle(Msg, State),  loop(NewState);  stop -> terminate(State)  end. terminate(State) -> clean_up(State). Start Stop Initialize Terminate Loop

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LINKS

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PidB PidA link(PidB)

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EXIT SIGNALS

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PidA PidB {'EXIT', PidA, Reason} PidC {'EXIT', PidB, Reason}

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TRAPPING EXIT SIGNALS

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process_flag(trap_exit, true) PidA {'EXIT', PidA, Reason} PidC PidB

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SUPERVISORS

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PidA PidC PidB Supervisor Workers

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erlang.org github.com/erlang/otp erlang-solutions.com www.learnyousomeerlang.org Erlang Programming Erlang and OTP in Action Official Home Page Sources Binary Packages, News, Events Best Online Tutorial Best book about basics Best book about OTP Where to Start

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Questions? @robertoaloi Cover Image: “How computers are made” (Reddit - Ness4114)