Ruby Concurrency and EventMachine

Ruby Concurrency...and the mysterious case of the Reactor Pattern Christopher Spring

WTF the EventMachineand why should I care?

Resource utilization • Lots of IO (90/10) • Disk • Network • system() • Lots of coreshttp://www.mikeperham.com/2010/01/27/scalable-ruby-processing-with-eventmachine/

Ruby concurrency basics • Threads • Fibers • Processes

Threading Models 1: N 1 :1 M :N

Threading Models 1: NKernel Threads 1 :1 User Threads M :N

Threading Models 1: N 1 :1 M :NKernel Threads User Threads

Threading Models 1: N • Green Threads • Ruby 1.8 1 :1 • Pros/Cons M :NKernel Threads User Threads

Threading Models 1: N 1 :1 M :NKernel Threads User Threads

Threading Models 1: N • Native Threads • Ruby 1.9 / jRuby 1 :1 • Pros/Cons M :NKernel Threads User Threads

Threading Models 1: N 1 :1 ? M :NKernel Threads User Threads

Threads

Threads• Shared state and memory space

Threads• Shared state and memory space• Relatively light weight

Threads• Shared state and memory space• Relatively light weight• Preemptive scheduling

Ruby has baggage: GIL http://www.igvita.com/2008/11/13/concurrency-is-a-myth-in-ruby/

Threads... suck

Threads... suck• Race conditions

Threads... suck• Race conditions• Deadlocks

Threads... suck• Race conditions• Deadlocks• Hard to debug

Threads... suck• Race conditions• Deadlocks• Hard to debug• GIL

Fibers

Fibers• It’s a coroutine, dammit!

Fibers• It’s a coroutine, dammit! • “... [component to] generalize subroutines to allow multiple entry points for suspending and resuming execution at certain locations.”

file_iterator = Fiber.new do file = File.open(stuff.csv, r) while line = file.gets Fiber.yield line end file.closeend3.times{ file_iterator.resume }# => line 1# => line 2# => line 3

Fibers• Cooperative Scheduling• Very lightweight• Maintains state• Great for: cooperative tasks, iterators, inﬁnite lists and pipes

def interpret_csv( csv_source ) Fiber.new do while csv_source.alive? str = csv_source.resume Fiber.yield str.split(,).map(&:strip) end endenddef file_iterator(file_name) Fiber.new do file = File.open(file_name, r) while line = file.gets Fiber.yield line end file.close endendinterpret_csv( file_iterator(stuff.csv) ).resume# => [...]

Reactor Pattern

Client Client Client Client IO StreamEvent Handler A Event DispatcherEvent Handler B DemultiplexerEvent Handler CEvent Handler D

Beneﬁts• Non blocking IO• Coarse grain concurrency• No threads!• Single Process

Limitations• Hard to debug• Dispatch to event handlers is synchronous• Demultiplexer polling limits

EventMachine

require eventmachineclass EchoServer < EM::Connection def post_init puts "New connecting" end def unbind puts "Connection closed" end def receive_data(data) # unbuffered!! puts "<< #{data}" send_data ">> #{data}" endendEM.run do EM.start_server(127.0.0.1, 9000, EchoServer) puts "Started server at 127.0.0.1:9000"end # Runs till EM.stop called

# $ telnet localhost 9000require eventmachine # Hello # >> Helloclass EchoServer < EM::Connection # Bye def post_init # >> Bye puts "New connecting" end def unbind puts "Connection closed" end def receive_data(data) # unbuffered!! puts "<< #{data}" send_data ">> #{data}" endendEM.run do EM.start_server(127.0.0.1, 9000, EchoServer) puts "Started server at 127.0.0.1:9000"end # Runs till EM.stop called

Primitives• run loop• next_tick; add_timer; add_periodic_timer• EM.defer• EM::Queue• EM::Channel

EM.run do Defer operation = Proc.new do puts MapMap!! sleep 3 puts Done collecting data [1, 1, 2, 3, 5, 8, 13] end callback = Proc.new do |arr| puts Reducing... sleep 1 puts Reduced puts arr.inject(:+) EM.stop end EM.defer(operation, callback)end

EM.run do Defer # # # MapMap!! Done collecting data Reducing... # Reduced operation = Proc.new do # 33 puts MapMap!! sleep 3 puts Done collecting data [1, 1, 2, 3, 5, 8, 13] end callback = Proc.new do |arr| puts Reducing... sleep 1 puts Reduced puts arr.inject(:+) EM.stop end EM.defer(operation, callback)end

EM.run do Queue queue = EM::Queue.new EM.defer do sleep 2; queue.push Mail 1 sleep 3; queue.push Mail 2 sleep 4; queue.push Mail 3 end mail_sender = Proc.new do |mail| puts "Sending #{mail}" EM.next_tick{ queue.pop(&mail_sender)} end queue.pop(&mail_sender)end

ChannelEM.run do channel = EM::Channel.new EM.defer do channel.subscribe do |msg| puts "Received #{msg}" end end EM.add_periodic_timer(1) do channel << Time.now endend

class Mailer include EM::Deferrable Deferrable def initialize callback do sleep 1 puts Updated statistics! end errback{ puts retrying mail} end def send rand >= 0.5 ? succeed : fail endendEM.run do 5.times do mailer = Mailer.new EM.add_timer(rand * 5){ mailer.send} endend

class Mailer include EM::Deferrable Deferrable def initialize # Updating statistics! callback do # Updating statistics! sleep 1 # retrying mail puts Updated statistics! end errback{ puts retrying mail} end def send rand >= 0.5 ? succeed : fail endendEM.run do 5.times do mailer = Mailer.new EM.add_timer(rand * 5){ mailer.send} endend

class Mailer Stacked callbacks include EM::Deferrable EM.run do def add_mailing(val) m = Mailer.new callback{ m.add_mailing(1) sleep 1; m.add_mailing(2) puts "Sent #{val}" m.connection_open! } end EM.add_timer(1) do m.connection_lost! def connection_open! EM.add_timer(2) do puts Open connection m.add_mailing(3) succeed m.add_mailing(4) end m.connection_open! end def connection_lost! end puts Lost connection end set_deferred_status nil endend

class Mailer Stacked callbacks include EM::Deferrable EM.run do def add_mailing(val) m = Mailer.new callback{ # Open connection m.add_mailing(1) sleep 1; m.add_mailing(2) # Sent 1 puts "Sent #{val}" m.connection_open! # Sent 2 } end # Lost connection EM.add_timer(1) do # Open connection m.connection_lost! def connection_open! # Sent 3 EM.add_timer(2) do puts Open connection m.add_mailing(3) # Sent 4 succeed m.add_mailing(4) end m.connection_open! end def connection_lost! end puts Lost connection end set_deferred_status nil endend

Gotchas• Synchronous code will slow it down • Use/Write libraries for EM• Everything in the event loop must be async!

Summary• It’s a blocking world!• Alternative concurrency implementations• Start playing with EM

Worth checking out• EM-Synchrony: https://github.com/igrigorik/em-synchrony• Goliath: https://github.com/postrank-labs/goliath

Baie Dankie!

Questions?

Links• http://www.mikeperham.com• http://www.igvita.com (!!)• http://rubyeventmachine.com/

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Ruby Concurrency and EventMachine

by Christopher Spring on Jun 18, 2011

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Ruby Concurrency and EventMachine — Presentation Transcript