Web, Concurrency, FP
May 31, 2013
Web, Concurrency, FP
May 31, 2013
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Web, Concurrency, FP the problems that we can’t ignore ...
any more (c) Alexey Kachayev, 2013
About me Alexey Kachayev •CTO at Attendify •Open source activist
(Fn.py) •Functional programming advocate •Erlang, Python, Scala, Clojure, Haskell, Go hacker
Contacts •kachayev <$> twitter •kachayev <$> gmail •kachayev <$> github
Disclaimer #1 It’s hard to tell “is this language functional?”
We will talk about: Erlang, Scala, Clojure, Haskell
Disclaimer #2 Web is only one way to communicate. We
will talk “mostly” about web. I assume that you know what “Web” is. Note, that it changes really fast.
Modern web challenges •real-time notiﬁcations •chats and other RT messaging
systems •real-time activity stream •collaborative documents editing •task board for team •multi-player Bomberman (* or your favorite game)
Concurrency... Concurrency is the composition of independently executing computations. Concurrency
is a way to structure software, ... (c) Rob Pike “Concurrency is not parallelism”
Concurrency is hard when independent computations depend on each other
WTF??? how independent computations can depend on each other?
Why should I care? I’m just coding Python/Ruby/PHP/ Node.js...
Classical web dev •Many OS processes •Database to store data
•.... •You are welcome in the world of concurrency!
So what? •Race condition on your data •Real-time is hard
(databases are not designed for this) •Leaking abstractions •Independency is expensive •No tests •No control
Java & .NET web dev •Threads instead of processes (VM
as OS???) •You can use memory for data collaboration •Necessity to control access to shared data leads you to locks/ mutex/semaphores
So what? •Independency is still too expensive •Still hard to
test •Still hard to control •Locks are not so good abstraction
Event- driven web dev •Single-thread environment •Event-based context switching loop
•Not so “independent” as we want •Errors are hard to manage •It’s hard to keep code simple to read
Do you need more problems? •request-reply doesn’t work (almost at
all) •concurrency is hard •fault-tolerance is hard •vertical scaling is hard (as well as horizontal) •everything should have been done yesterday
How to deal with concurrency?
Story about developers and tasks board •Locks: what is locks
and why it’s not a good idea? •Message passing: how to communicate and what are the beneﬁts? •STM: how to collaborate efﬁciently and not lose control?
From theory to practice
Concurrency •Erlang •Scala •others •Clojure •Haskell •others Communication Collaboration And
why do FP “features” matter?
Erlang •message-passing concurrency •multi-core support •distributed systems •“super” stable VM
(VM as OS!) •“hard to break” something •interactive development
Scala • JVM based, high performance • (mostly) functional paradigm
• expressive type system (ADT & TI) • “less code with more results” • message-passing concurrency (prev. Akka) • ... XML is native Scala type
Reactivity or “super- thin” client •Liftweb (Scala) •Nitrogen (Erlang) •N2O
Clojure •FP, lisp-family •STM concurrency model •modern language •interactive development
Haskell •FP, “ML-family” •green threads and STM •expressive type system
•high level of code modularity and composability •compact declarative syntax •compile-time program veriﬁcation
How to start? •do not wait! •do not hesitate! •do
not panic!!! •do something simple •do something interesting •ﬁnd problem (pain?) and solve it
Links • https://github.com/extend/cowboy • http://nitrogenproject.com/ • http://liftweb.net/ • https://github.com/twitter/ﬁnagle •
http://www.scalatra.org/ • https://github.com/ring-clojure/ring • https://github.com/weavejester/ compojure • http://pedestal.io/ • http://himera.herokuapp.com/ synonym.html • http://snapframework.com/
Questions? * other talks: https://kachayev.github.com/talks ** me: http://twitter.com/kachayev P.S. We