actorsandthreads

Actors & Threads @mperham

Concurrency
 Two primatives: processes, threads
 Problem: communication and coordination
   Shared data, copied
 
IPC 
  pipes, sockets, shared mem, files

Threads
  More efficent than processes
  POSIX doesn't define comm mech
    Locks

Runtime efficiency not only goal

Locks
  Hard to get right
  Non deterministic
  Don't scale

Thread contention
  Not in 1.9 due to GIL, in Jruby penalize for contention and context switch

Thread communication
  Go: goroutines
    Anonymous function, no handles to it.
    Pass messages via channels
    Maps well to distributed model (no handle on db, but can get socket)
    Backed by thread pool
  Actors
    Unit of executon
    mailbox
    send message
      actor << { :amount => 123 }
    Thread or fiber backed
    No application locks (message copied)

MRI/Jruby
  No actors

Rubinius (actor.rb)
  Not idiomatic, hard to understand

Celluloid
  OO actors
  async method invocation 
  mix of threads & fibers 
  One object == one thread (.5Mb per thread)
  Needs actor pooling.

girl_friday
  Background processing poll
  Parallel batch operations
  Functional over OO
  Thread based
 
Software Transactional Memory
  Mutation of data in a transaction
  ACI, not ACID
  Clojure

Atomic Instructions
  XCHG swap registers
  CPMXCHG compare and set
  JRuby has AtomicInteger, (#incrementAndSet)

java.util.concurrent
  concurrent hash map, concurrent linked queue

TODO 
  Standard Actor API
  Concurrent DS
  STM for Ruby (jruby)
    Multiverse

Reading
  Kilim
  Disruptor
  Actors in Scala
  Concurrency in Erlang