gpars - the coolest bits

The coolest bits

Why bother!?

GParsGroovy Parallel Systems- multiple high-level parallelism abstractions- Java-usable- GAE-usable- part of Groovy SDK- open source (Apache 2 License)- Grooovy documentation

GParsGroovy Parallel Systems

Team: Václav Pech, Dierk König, Russel Winder,Alex Tkachman, Paul King, Jon Kerridge,Rafał Sławik and others

One Ring to rule them all...Parallelism approach in GPars (originally?) found in implemented using

Parallel collections Scala, Java jsr-166y / JDK5 executors

jsr-166y Fork/Join (sugar) Java jsr-166y

Actors Erlang, Scala java.util.concurrent

Software Transactional Memory Clojure, Scala Multiverse

Agents Clojure java.util.concurrent

CSP CSP :) Dataflow* or JCSP

Dataflow and extensions:Pipelines, Kanbanflow

Linda, Verilog, Agilent Vee, Scala, Unreal Engine

jsr-166y / JDK5 executors (?)

Composable asynchronous functions ? jsr-166y / JDK5 executors

Our focusParallelism approach in GPars (originally?) found in implemented using

Parallel collections Scala, Java jsr-166y / JDK5 executors

jsr-166y Fork/Join (sugar) Java jsr-166y

Actors Erlang, Scala java.util.concurrent

Software Transactional Memory Clojure, Scala Multiverse

Agents Clojure java.util.concurrent

CSP CSP :) Dataflow* or JCSP

Dataflow and extensions:Pipelines, Kanbanflow

Linda, Verilog, Agilent Vee, Scala, Unreal Engine

jsr-166y / JDK5 executors (?)

Composable asynchronous functions ? jsr-166y / JDK5 executors

Demo time!Enabling GPars GDSL in Intellij IDEA

Demo time!Parallel collections- withPool / enhancer- makeConcurrent / makeSequential /

asParallel- GParsPool + ParallelEnhancer /

GParsExecutorsPool + GParsExecutorsPoolEnhancer

- Map-Reduce (Fork / Join pool only)

Things to consider / a warning...

In this approach, your iteration body must be:- stateless- side-effect free- constrained to the current elementElse - welcome to concurrency hell...

Demo time!Agents- updating immutable / mutable- syntax equivalents for .send- copy method- parallel behaviour- error handling- parallel groups, daemon threads & shutting

down

Agents - what else is there- listeners- validators & validation gotchas- non-closure sends- prefer composition over inheritance- sendAndAwait

Agents - Q & AQuestions?- what if I want to check a condition

before updating state?- how do I 'lock' the state?

Composable Asynchronous Functions- @AsyncFun / asyncFun()- async funs return DataflowVariable-s- blocking @AsyncFun-s for convenience- rest of the docs: instantiation variants,

pool configuration

Demo time!

Bonus: on parallelism flavours

Choosing an approachTask parallelism

Independent Async closures, Futures, whatever...

Dependent Random / Unknown Dataflow

Functional / Linear Composable asynchronous functions, Dataflow tasks, CSP

Hierarchical / Recursive Fork / Join

Shared state Agents, STM

Choosing an approachData parallelism

Geometrical / Linear Parallel collections

Hierarchical / Recursive Fork / Join

Streamed (regular) Pipeline DSL, Dataflow, CSP

Event-driven (irregular) Actors

From GPARS User Guide

TL;DRParallel collectionsAsync functionsDataflowAgentsMessage passing - CSP - Dataflow - Actors

Also: Bashing actors a little :)

Actors are overratedDierk König

Also: Bashing actors a little :)Why there were no Actors in Clojure*● complex● no efficient sharing even for immutable structures● reduce flexibility● do not really distribute well from single to many

machines

* a purposefully exaggerating summary by me

Slides since Morpheus based on● Václav Pech - GPars How To Guide● Paul King - Concurrency with GPars● GPars User Guide - Applicability of concepts● GPars docs - Concepts compared● Dierk König - Concurrent programming for you and me● my personal biases :)

Recap- GPars is quite a lib :)- Be sure to try Dataflows- Actors are overrated ;)

Questions?

Thank you!