gpars: groovy parallelism for java
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GPars: Groovy Parallelism for Java
Groovy Parallelism for Java
Prof Russel WinderDirectorIt'z Interactive Ltd
t: @russel_winder
Prof Russel Winder
Company director, independent consultant, analyst, author,
expert witness, trainer, mentor,
Involved with GPars, Groovy, Gant, Gradle, GroovyFX,
Python, SCons
Ex-theoretical physicist, ex-UNIX systems programmer,
ex-computer science academic. Still human.
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Introduction
Concurrency
A technique for doing lots of little bits of work,
one at a time, and then leaving them for later.
Co-routines.
Concurrency
Concurrency is also a technique for
simulating parallelism on a uni-processor.
Time-division multiplexing.
Concurrency
Locks, semaphores, monitors all introduced to manage shared mutable memory in the presence of concurrency.
Operating systems techniques.
Parallelism
Having more than one thing happening at the same time: multiple processors or cores working on a single program at the same time.
The only reason for
using parallelism is
to make computations
take less time.
Observation
Squirrels use locks when managing their food resources.
Some
Interaction
Question
Who is interested in harnessing parallelism
for performance improvement?
Question
Who uses synchronized in Java?
Question
Who uses synchronized in Java?
You are doing it wrong.
Question (with subsidiaries)
Who uses explicit locks in Java?Who is not using java.util.concurrent?
Who is using java.util.concurrent?
Question (with subsidiaries)
Who uses explicit locks in Java?Who is not using java.util.concurrent?
Who is using java.util.concurrent?
You are definitely doing it wrong.
Rationale
The purpose of locks is to prevent parallelism.
Locks prevent performance improvement.
Consequence
Squirrels deny parallelism of consumption.
Squirrels deny performance improvement.
Being
Positive
Forward Looking
Can Java 8 make things better?
Java 8 Streams
Internal rather than external iteration.
Functional programming approaches.
Threads as infrastructure.
This is the real biggy,programmers do not
explicitly manage threads.
Example
What is the value of ?
Easy, it's obviously.
It's simples
2009
Approximating ?
Find an estimate of the value of .
Approximate an integration with a summation.
Quadrature
Embarrassingly parallel
Addition is associative and commutative.
Sum all the areas of the rectangles.
a + b + c + d = (a + b) + (c + d)
Can sum partial sums.
Parallelism
Scatter/gather
Farmer/worker
Fork/join
Map/reduce
Code
Software Architectures
ActorsIndependent processes communicating via asynchronous exchange of messages.
CSPSequential processes connected by channels using synchronous message exchange (rendezvous).
DataflowOperators connected by channels with activity triggered by arrival of data on the channels.
Data ParallelTransform a sequence to another sequence where all individual actions happen at the same time.
Software Architectures
Data ParallelTransform a sequence to another sequence where all individual actions happen at the same time.
Software Architectures
ActorsIndependent processes communicating via asynchronous exchange of messages.
Software Architectures
DataflowOperators connected by channels with activity triggered by arrival of data on the channels.
Software Architectures
CSPSequential processes connected by channels using synchronous message exchange (rendezvous).
Software Architectures
Active ObjectsAn object that is actually an actor but looks like a full service object.
AgentsA wrapper for some shared mutable state.
Software Transactional MemoryWrappers for mutable values that uses transactions rather than locks.
Fork/JoinAn toolkit for tree structured concurrency and parallelism.
More
Code
Mantra
Squirrels deny parallelism.
Squirrels deny performance improvement.
Programmers' code should not emulate squirrel behaviour.
Endnote
Source Code
The sample codes are in a Git repository on
GitHub and my own website.
The End
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Groovy Parallelism for Java
Prof Russel WinderDirectorIt'z Interactive Ltd
t: @russel_winder
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