Actors and Threads

Actors and Threads Safer Concurrency for Ruby Mike Perham @mperham

Who Am I?• Numerous gems (dalli, memcache-client, rack-ﬁber_pool, connection_pool, etc)• Scalability/Performance guy• Fibers and EventMachine• Technical Lead at Carbon Five

Ruby History• Fun!• Implementation • Performance • Scalability

What This Isn’t• Threads vs Events vs Processes• Threads won’t make you love Java

Deﬁnitions• Concurrency - performing two operations in tandem (e.g. two web requests)• Parallelism - performing two operations literally at the same time (requires two cores) Concurrent Parallel

Concurrency• Processes• Threads

The problem is always communication (true in the real world too!)

Communication• Two fundamental mechanisms • Share • Copy

IPC• Pipes• Sockets• Shared Memory• Files• POSIX 1988

Threads• Much more efﬁcient than processes• Communication mechanism? • Variables!• POSIX 1995

Threads

End Goals• Runtime Efﬁciency isn’t the only goal!• Remember Fun?• Ease of Development is huge

Locks• Hard to get right• Non-deterministic• Don’t scale

Lock Benchmark# Results: Ruby 1.9.2, GIL means no parallel threading# user system total real# single locked 4.310000 0.010000 4.320000 ( 4.311850)# threaded locked 4.230000 0.080000 4.310000 ( 4.307405)## Results: JRuby 1.6.3, parallel threads mean massive lock contention# user system total real# single locked 4.080000 0.000000 4.080000 ( 4.080000)# threaded locked 17.109000 0.000000 17.109000 ( 17.109000) Context Switching!

Most Important Slide!

What can we do?• Look to other languages • Go • Scala • Erlang

Goroutines• Asynchronous function • You cannot get a handle to it • Send messages via a channel

Goroutines• Really like this model• Maps well to a distributed model• Backed by a pool of threads

Actors• unit of execution• has a mailbox• You just send it a message, e.g. • actor << { :amount => 11.99 }

Actors• Thread- or Fiber-backed• No application-level locks

Actor.rb• MRI/JRuby - no actors• Rubinius comes with actor.rb

Actor.rb

Actor.rb• Not idiomatic• Hard to understand, use correctly

Celluloid• Tony Arcieri (Revactor, Reia)• https://github.com/tarcieri/celluloid• OO Actors• Asynchronous method invocation• Mix of Threads and Fibers

Celluloid Example

Celluloid Thoughts• Nice, idiomatic Ruby design• One object == one thread• Needs actor pooling

girl_friday• yours truly• http://github.com/mperham/girl_friday• Background processing pools• Parallel batch operations• More functional than OO• Thread-based

girl_friday example

What if we do need to share data?

I Love the 80s!

I Love the 00s!

STM• Software Transactional Memory• All mutation via transactions• Provide ACI (not ACID) guarantees• See Clojure (and Cloby!)

Atomic Instructions• Since Pentium (1993)• XCHG - swap registers or register/ memory• CPMXCHG - Compare And Set (‘CAS’)

Atomic!

Atomic Benchmark# Results: JRuby 1.6.3# user system total real# single atomic 2.041000 0.000000 2.041000 ( 2.041000)# threaded atomic 0.978000 0.000000 0.978000 ( 0.979000) 2 cores = 2x speedup!

Atomic Structures• java.util.concurrent • ConcurrentHashMap • ConcurrentLinkedQueue

Conclusion

Concurrency It’s always hard! Modern languages should supporttools and APIs that scale well AND are developer-friendly.

To Do• Need standard Actor API• Concurrent data structures• STM impl for Ruby (via JRuby?) • Multiverse

Further Reading• Kilim - Actors for Java• Disruptor - concurrency without locks• Actors in Scala• Concurrency in Erlang

Thank You! Questions? @mperham http://mikeperham.comhttp://blog.carbonﬁve.com PS We’re hiring!

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Actors and Threads

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