Functional Programming & Concurrency Patterns

Tim Kellogg (@kellogh)September 2, 2014

Agenda• Introduce 2lemetry & IoT technologies• Introduce Scala• Functional Programming• Concurrency patterns

About Me• 39.9747597,-105.0881511• Class of 2007

Internet of Things• Moving• Storing• Analyzing• Reacting

MQTT• Message Queue Telemetry Transport• Pub/Sub binary protocol• Open standard• Persistent connections

IoT-SQLSELECT LAST(*) FROM mqtt(‘co.t/temp/+’) AS tempJOIN storage(‘metadata’) AS md ON temp.deviceId = md.idWHERE temp.outside.value > 90 AND temp.inside.value < 70GROUP BY 1 HOUR

We need…• To move quickly, be agile, adapt to changes• Performant code• To leverage concurrency • To rent server space in the cloud

• Functional + Object Oriented• Strongly typed– Safe– Not like Java types

• JVM

• First-class functions• Traits• Type inference• Record types (case classes)• Pattern Matching (and structural typing)

Record Types

Pattern Matching

First class functions

First Class Functions

Example:Count all goals from young players

Example: Count Goals

Example: Count Goals

Example: Count Goals

Example: Count Goals

Example: Count Goals

Example: Count Goals

Example: Count Goals

Example: Count Goals

Example: Count Goals

Example: Count Goals

Example: Count Goals

FP Mainstream References• SQL• LINQ (C#)• jQuery• Hadoop (map / reduce)– Spark

Monads

Common Monads• List[T]• Set[T]• Option[T] No more nulls• Future[T]• Try[T]

Monads• Container• “bind” operation– “flatMap” in Scala– T => M[U]

List[T] As A Monad

Option[T] As A Monad

Option[T] As Monad

List[T] As A Monad

List[T] As A Monad

Concurrency

Concurrency Basics• If it’s immutable, it’s thread-safe• Locks are hard to reason about• Badly placed locks defeat concurrency

Multi-threading vs Concurrent• Concurrent– An architecture– Not necessarily multi-threaded

Immutability: What You Can’t Do• Change a variable• Write to a file• Write to a TCP socket

Haskell Is Useless

Simon Peyton Joneshttps://www.youtube.com/watch?v=iSmkqocn0oQ

Side Note: Reference Immutability• https://homes.cs.washington.edu/~csgordon/

papers/oopsla12.pdf

• M#• Rust

Immutability: What You Can Do• State Monad• IO Monad• Future Monad• Forget about concurrency details

Role of Monads• Represent state as a value• Declarative programming– Describe the problem– Let the compiler solve it for you

Future[T]• Represents a value• Handles failure as a value• Computation might happen on another thread• Supervisors

Future[T]• map / filter• flatMap (bind)• successful (pure)

Future[T]

Future[T] - Dispatchers• Thread pooling• Configuration

Actors

Actors• Akka (Scala)• OTP (Erlang)• http://arxiv.org/pdf/1008.1459.pdf • “Sandboxing” mutability & side effects

Actor Model of Computation

Actor Mailbox

Akka

Akka Specialization• Actors Computation• Dispatchers Thread pooling• Supervisors Reliability• Routers Concurrency