Erlang.

Measurements and benefits

Valerii Vasylkov, Timecode LLC.

History notes

Erlang shots

Erlang benefits

Functional naturePattern matching on steroidsConcurrencyFault ToleranceLet it crashDistributed ComputationDebugging and profilingHot upgrades

Erlang benefits

Functional naturePattern matching on steroidsConcurrencyFault ToleranceLet it crashDistributed ComputationDebugging and profilingHot upgrades

Functions are easy

Dynamic typesPattern matchingNo mutable datastructures

Binary tree search

Factorial function

Erlang benefits

Functional naturePattern matching on steroidsConcurrencyFault ToleranceLet it crashDistributed ComputationDebugging and profilingHot upgrades

Pattern matching and steroids

Structures

Binaries

Complex conditions

1 get_vh_registered_users(Server, [{prefix, Prefix}, {limit, Limit}, {offset, Offset}]) 2 when is_list(Prefix) and is_integer(Limit) and is_integer(Offset) ->3 case [{U,S} || {U, S} <- get_vh_registered_users(Server), lists:prefix(Prefix, U)] of4 [] ->5 [];6 Users ->7 Set = lists:keysort(1, Users),8 L = length(Set),9 Start = if Offset < 1 -> 1;10 Offset > L -> L;11 true -> Offset12 end,13 lists:sublist(Set, Start, Limit)14 end.

* Not your familiar Regex string matching

Erlang benefits

Functional naturePattern matching on steroidsConcurrencyFault ToleranceLet it crashDistributed ComputationDebugging and profilingHot upgrades

Erlang concurrency philosophy

The Actor Model

Thinking Parallel

Thinking Processes

• Behavior• State• Parallel• Asynchronous Messages Mailboxes• No Shared State

The Actor ModelCarl Hewitt

1973

• Data + Code + Process • Self-Contained Machines • Stronger Encapsulation • Less Inheritance• Type Inference• Hot Code Upgrades

Actor structure

Behavior way

• Inheritance of Behavior only.• Usually only one level deep.• Usually one of the standard OTP behaviors:

• Generic Server• Event• State Machine• Supervisor.

Actor vs. OO workflowSynchronous Calls

Asynchronous Messages

Actor Model: Benefits

• More true to the real world• Better suited for parallel hardware• Better suited for distributed architectures • Scaling garbage collection (gc/actor)• Less Magic

Actors example-module(pingpong).-export([start/0]).-export([ping/0, pong/0]).

start()->PingPid = spawn(?MODULE, ping(), []),PongPid = spawn(?MODULE, pong(), []),PingPid ! {ping, PongPid},erlang:send_after(60000,PingPid, stop),erlang:send_after(60000,PongPid, stop).

ping()-> receive {Pid, ping} -> io:fwrite("Ping received Pong~n",[]), timer:sleep(3000), Pid ! {self(), pong}, ping(); stop -> true end.

pong() -> receive {Pid, pong} -> io:fwrite("Pong received Ping~n",[]), timer:sleep(3000), Pid ! {self(), ping}, pong(); stop -> true end.

Erlang benefits

Functional naturePattern matching on steroidsConcurrencyFault ToleranceLet it crashDistributed ComputationDebugging and profilingHot upgrades

Fault-tolerant Erlang

Supervisors

Links and Monitors

Erlang benefits

Functional naturePattern matching on steroidsConcurrencyFault ToleranceLet it crashDistributed ComputationDebugging and profilingHot upgrades

Faulty subsystem are difficult to correct

P.S. Don’t bother, just restart

Erlang benefits

Functional naturePattern matching on steroidsConcurrencyFault ToleranceDistributed ComputationDebugging and profilingHot upgrades

Distribution

Node 1 Node 2

B ! MsgA B C

transparent message passing in cluster

Setting up an Erlang clustererl -sname ketchup...(ketchup@ferdmbp)1>(ketchup@ferdmbp)1> net_kernel:connect_node(fries@ferdmbp).true

(ketchup@ferdmbp)2> node().ketchup@ferdmbp(ketchup@ferdmbp)3> nodes().[fries@ferdmbp]

(ketchup@ferdmbp)4> register(shell, self()).true

(ketchup@ferdmbp)5> {shell, fries@ferdmbp} ! {hello, from, self()}.{hello,from,<0.52.0>}

(ketchup@ferdmbp)6> flush().Shell got <<"hey there!">>ok

erl -sname fries...(fries@ferdmbp)1>

(fries@ferdmbp)1> register(shell, self()).true

(fries@ferdmbp)2> receive {hello, from, OtherShell} -> OtherShell ! <<"hey there!">> end.

http://learnyousomeerlang.com/distribunomicon

Erlang benefits

Functional naturePattern matching on steroidsConcurrencyFault ToleranceDistributed ComputationDebugging and profilingHot upgrades

Observer

Remote shells

(salad@ferdmbp)1>User switch command--> hc [nn] - connect to jobi [nn] - interrupt jobk [nn] - kill jobj - list all jobss [shell] - start local shellr [node [shell]] - start remote shellq - quit erlang? | h - this message--> r mustard@ferdmbp--> j1 {shell,start,[init]}2* {mustard@ferdmbp,shell,start,[]}--> cEshell V5.8.4 (abort with ^G)(mustard@ferdmbp)1> node().mustard@ferdmbp

Debugger and profilers

Tool Results Size of Result

Effects on Program Execution Time

Records Number of Calls

Records Execution Time

Records Called by

Records Garbage Collection

fprofPer process to screen/file Large Significant slowdown Yes Total and

own Yes Yes

eprofPer process/function to screen/file Medium Small slowdown Yes Only total No No

coverPer module to screen/file Small Moderate slowdown Yes, per line No No No

cprof Per module to caller Small Small slowdown Yes No No No

dbg Text based tracer Large Small slowdonw No No Yes No

Community

• recon• redbug• lager• xprof

More introspection

• etop• pman• os_mon• debugger

Bottleneck detection

Erlang benefits

Functional naturePattern matching on steroidsConcurrencyFault ToleranceDistributed ComputationDebugging and profilingHot upgrades

Hot code upgrades

Erlang applications pie

Measurements

Activity

• millions active users• fast processes for handling

Stability

• developers and operations sleeps fine• no emergencies for a couple of years

Performance

• compatible to C, • VM memory management• lightweight concurrency• scalability from a box

Issues

• concurrent bottlenecks• Net splits• Networks security• Hot upgrades

Top 5 lines of code

4629211703732827841479

Questions?