Erlang - Concurrent Language for Concurrent World
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Intro to Erlang talk from Erlang Factory Lite Tel-Aviv, October 23 2013
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Erlang - Concurrent Language for Concurrent World
- 1. $ whoami Name: Zvi Avraham Title: Founder & CEO Company: ZADATA Ltd E-mail: zvi@zadata.com
- 2. Concurrent Language for Concurrent World
- 4. The world is concurrent… I could not drive the car, if I did not understood concurrency … -- Joe Armstrong, father of Erlang
- 10. Imagine a programming language which allows only 1000 objects -- Joe Armstrong, father of Erlang
- 11. COP vs OOP Concurrency-oriented vs Object-oriented • 15 years ago OOP became mainstream • COP became popular only recently • Process is active object – i.e. object with it’s own process of control – Objects in OOP are “passive objects” • Processes as cheap as hashtables: – ~ 300 words (1.2KB) per process by default – max 134M processes per VM (limited by RAM)
- 12. Concurrency-oriented Programming • Large number of processes (up to millions) • Complete isolation of processes • No shared memory • Copy message data between processes – instead of just passing pointer to message • Avoid sequential bottlenecks • Location transparency
- 13. Share Nothing! No mutable State!
- 15. But, it will not help if the whole VM crashes
- 16. One Process per Parallel Activity • try to do only one thing per process • If you need to do something – just spawn a new process • no thread pools!
- 18. Let it crash! • all sequential languages get error handling wrong! • No defensive programming! • If you don’t know how to recover from the error – let it crash!
- 19. Lenin – Lived Lenin – is Alive Lenin – will Live!
- 20. Errors – Existed Errors – Exist Errors – will Exist!
- 21. Lenin, read my dissertation: “Making reliable distributed systems in the presence of software errors”
- 23. Erlang Timeline 1984 1986 1987 1991 1993 OTP 1996 1998 2007 Open SourceDistributed Erlang Early Erlang Prototypes First fast implementation CS Lab Experiments AXD301 switch
- 24. Erlang/OTP Stack Erlang VM – BEAM / ERTS Functional Sequential Erlang Concurrent Erlang OTP – Open Telecom Platform Distributed Erlang ErlangProgrammingLanguage
- 26. Functional Sequential Erlang • Data types: –Integers (incl. BigNums), floats, atoms –tuples/records, lists/plists, binaries, funs –Maps (added in R17) • single assignment • pattern matching & guards • closures (anonymous function data type) • list comprehensions • bit-syntax & binary comprehensions • tail recursion & tail call optimization (TCO)
- 27. Single Assignment1> X. * 2: variable 'X' is unbound 2> X = 10. 10 3> X = X + 1. ** exception error: no match of right hand side value 11 4> X = X. 10 5> X = 10. 10 6> X = 20. ** exception error: no match of right hand side value 20
- 28. No Loops???
- 29. No Loops??? • Use instead: –recursion and tail recursion –list comprehensions –binary comprehensions –Higher-order Functions (HOFs): • map/foldl/foldr/zip/filter/etc. • For example: [ io:format(“~b”,[I]) || I<-lists:seq(1,10) ].
- 30. RECURSION
- 31. RECURSION
- 35. Tail Recursion
- 37. zvi@host:~$ erl Erlang R16B02 … … 1> c(demo). {ok,demo} 2> demo:fact(0). 1 3> demo:fact(5). 120 4> demo:fact(-10). ** exception error: no function clause matching demo:fact(-10) (demo.erl, line 10)
- 39. OOP vs FP
- 40. Side-Effects • Erlang is not pure-functional language • “Controlled Side effects”: – Messages - Pid ! Msg – send message to process Pid – Signals - i.e. your linked process is dead – Exceptions – I/O – Process Dictionary - similar to TLS (thread local storage) – ETS / DETS - fast in-memory / persistent lookup tables – Mnesia - distributed realtime database (sort of STM)
- 42. Erlang Source Code Structure • OTP Release (self-contained tar.gz archive) – OTP Application (directory structure) • Module (file sources in *.erl, compiled in *.beam) – Function » Clause (syntactic sugar for case statement)
- 43. MFA • Module:Function/Arity • Module:Function(Arguments) • M:F(A1,A2,..,An) = apply(M,F,[A1,A2,..,An])
- 44. Concurrent Erlang • Spawn processes • Send messages to processes • Selective receive • Additional data types: – PIDs, references
- 45. Spawn a process
- 46. Send Message
- 47. Receive Message
- 49. Actors / Agents / Active Objects
- 50. Process • Pid – Process ID • optional: registered name • initial call: MFA • message queue (mailbox) • stack • heap • Dictionary (like TLS – thread local storage) • traping exits? (boolean flag) • linked processes • priority (low/normal/high) • Reductions counter
- 51. Distributed Erlang Erlang Run-Time System Erlang Run-Time System network A B C Node name: foo@domain.com Node name: bar@domain.com
- 52. Distributed Erlang Erlang Run-Time System Erlang Run-Time System B ! Msg network A B C Node name: foo@domain.com Node name: bar@domain.com
- 53. Distributed Erlang Erlang Run-Time System Erlang Run-Time System B ! Msg network C ! Msg A B C Node name: foo@domain.com Node name: bar@domain.com
- 54. Erlang VM - SMP Schedulers
- 55. zvi@host:~$ erl Erlang R16B02 (erts-5.10.3) [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false] Eshell V5.10.3 (abort with ^G) 1>
- 57. Hot Code Reloading • Module may have 2 version loaded in VM: – old version – current version • When new version of module is loaded: – it become a “current version” – current version become the “old version” • All new processes will use current version • The old processes running old version – In places in the code where module name is explicitly specified - the process will switch to current version: • my_function(Args) - no version switch • my_module:my_function(Args) - switching version
- 58. Tools • IDE: – Emacs, Distel, Plugins for Eclipse and Netbeans • Testing: – e-unit, meck, proper, QuickCheck (paid), Quick Check mini - free • Static code analyzer: – Dialyzer • Debug and trace – Built-in in VM – dbg, redbug • Build: – emake, rebar, relx, erlang.mk • Package Managers: – rebar, mix
- 59. ERLANG RESOURCES Docs, Tutorials, Community, Conferences
- 72. Erlang/OTP is a good fit for: • Irregular concurrency: – Task-level – Fine-grained parallelism • Network servers • Distributed systems • Middleware: – Parallel databases – Message Queue servers • Soft Realtime / Embedded applications • Monitoring, control and testing tools
- 73. Not so good fit for: • Concurrency for synchronized parallel execution – Data Parallelism • Floating-point intensive code (HPC) • Text Processing / Unicode – Unicode support now much better • Traditional GUI (supports wxWidgets) • Hard Realtime applications • Extensive interop with other languages/VMs – improvement here with NIFs and Erjang - Erlang on JVM
- 74. Thank You! Now Q&A All images are taken from Google Image search and various other places on the Internet © Copyright of corresponding owners
- 75. BACKUP SLIDES
- 76. Communicating with External world: • Part of the OTP: – CORBA/IDL – ODBC/SQL – ASN.1 – SNMP – HTTP/FTP – SSH • erlcall – execute any Erlang function on remote Node from the shell or script • escript – write scripts in Erlang – no need to compile
- 77. Communicating with External world In-proc Out-of-proc Custom Protocol Linked-in Drivers • in-proc (.so, DLLs) • Written in C • custom protocols • Can crash VM Ports • external executable • like pipes • custom protocols via fd/stdio/sockets • Dir = os:cmd(“ls –al”). Generic Protocol NIF • Native Implemented Functions • Written in C • in-proc (like JNI in Java: .so, DLLs) • .so/DLLs can be hot code reloaded at runtime • can block a scheduler • Can crash VM C-Node • out-of-proc (external executable, interpreter or VM) • Pretend to be a distributed Erlang node (but implemented in other lang.) • JInterface (Java), OTP.NET, PyInterface (Pyton), Ruby- electricity, etc. • Example: erlcall
- 79. Erjang – Erlang for JVM
- 80. Erlang-on-Xen / ling VM
- 81. LuvvieScript - Erlang to JS compiler
- 82. LANGUAGES FOR ERLANG VM
- 86. Elixir Books
- 87. COMPARISON Concurrent Programming: Scala+Akka, node.js, Go
- 92. Go-lang
- 93. Erlang / Elixir Clojure Scala Node.js Go-lang Paradigm Functional COP Functional Functional OOP CBoP OOP ImperativeO OP? Type system dynamic dynamic static dynamic static Target BEAM JVM JVM Chrome V8 native Multithreading yes yes yes no Yes Built-in Asynch I/O yes no no yes yes Lightweight processes yes Partial* no no yes Soft-RT GC yes no no no no Pattern Matching yes no yes no no OTP analogue? Yes - OTP Akka? Akka? no no Tools Middle Elixir - better good middle good excellent Problem Domain usually used Messaging, Distributed Systems Unstruct. data Big Data: Kafka, Spark Web apps / Realtime Web DevOps