This document is an introduction to a workshop on dataflow programming. It begins with an introduction of the presenter and their background. It then defines dataflow programming as an event-based architecture where processes run when data is available via input channels and output to output channels. The document outlines the agenda for the workshop which is to experiment with dataflow concepts using Groovy and Java and discuss how hiding threading through reactive processes can be useful. It concludes by encouraging attendees to continue exploring dataflow programming approaches.

1. 01—Introduction
Dataflow
The Forgotten Way
Dr Russel Winder
russel@winder.org.uk
@russel_winder
http://www.russel.org.uk
Copyright © 2014 Russel Winder 1
Introduction
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c 2014 Russel Winder Printed for JAXLondon 2014 Workshop 2014-10-13 01–01

2. 01—Introduction
Russel Winder — 1/2
● Ex:
– Theoretical physicist
– UNIX system programmer
– Academic (UCL, KCL)
– Start-up CTO
● Current:
– Independent consultant
– Analyst
– Author
– Expert witness
– Trainer
Copyright © 2014 Russel Winder 3
Russel Winder — 2/2
● Groovy
– Groovy
– GPars
– GroovyFX
– Gant
● Java
● Python
– SCons
– PythonCSP
● D
● Go
● Kotlin
● Ceylon
● Rust
● C++
FOSS activity
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3. 01—Introduction
Attenders
● Name.
● Rank.
● Serial number.
● Your programming
background.
● Why is this workshop
interesting for you?
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So what is dataflow?
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4. 01—Introduction
Dataflow
● Originally a computer
hardware architecture:
– Manchester dataflow
machine.
J. R. Gurd, C. C. Kirkham,
and I. Watson, CACM, 28(1),
1985-01
● Originally a systems
analysis technique:
– Tom DeMarco,
Structured Analysis and
System Specification,
1979.
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Event-based.
Channels
aka
Flows
Processes
Processes process when data is ready on the input
channels, putting data on the output channels.
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5. 01—Introduction
Concurrency and Parallelism Models
● Actors
● Data parallelism
● Communicating
Sequential Processes
(CSP)
● Dataflow
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Why is dataflow forgotten?
● Shared memory
-multithreading:
– People indoctrinated
into thinking threads
had to be explicitly
managed in code.
– Increasingly, thread
pools, and work stealing,
seen as a better model.
● Actors:
– A good and useful high
level concurrency and
parallelism architecture,
but…
– Has a very specific
asynchronous underlying
model, useful for some
solutions, not other.
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6. 01—Introduction
This Workshop
Play† with dataflow using:
– Groovy
– GPars
– Java
To investigate how useful hiding threads under a
reactive process system can be.
† It is mandatory that we have fun in this workshop.
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Environment
● Editing:
– Emacs, VIM, Sublime
Text, Notepad++,…
– Eclipse, IntelliJ IDEA,
Netbeans,…
● Languages:
– Java 8†
– Groovy 2.3.6 (GPars is
included :-)
● Build:
– Manual command line
– Gradle
† Java 7 allowed if you really have to.
Using whatever Groovy
and Java add-ins…
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7. 01—Introduction
Time to ensure we are all
ready to do stuff…
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8. 02—Dataflow
Dataflow
The Forgotten Way
Dr Russel Winder
russel@winder.org.uk
@russel_winder
http://www.russel.org.uk
Copyright © 2014 Russel Winder 1
Dataflow
Copyright © 2014 Russel Winder 2
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c 2014 Russel Winder Printed for JAXLondon 2014 Workshop 2014-10-13 02–01

9. Event-based.
02—Dataflow
Channels
aka
Flows
Processes
Processes process when data is ready on the input
channels, putting data on the output channels.
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We need a problem…
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10. 02—Dataflow
Calculating Means
● Mean of a set of data is:
x=1
n
xi
nΣi
=1
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Code…
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c 2014 Russel Winder Printed for JAXLondon 2014 Workshop 2014-10-13 02–03

11. 02—Dataflow
Time to try something
for ourselves…
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Calculating Mean and
Standard Deviation
● Mean of a set of data is:
● Standard deviation is:
x=1n
n
xi
Σi
=1
s=√ 1
n
(xi−x)2
n−1Σi
=1
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c 2014 Russel Winder Printed for JAXLondon 2014 Workshop 2014-10-13 02–04

12. 02—Dataflow
Calculating Mean and
Standard Deviation
● Mean of a set of data is:
● Standard deviation is:
x=1n
n
xi
Σi
=1
s=√ 1
n
xi
n−1 ((Σi
=1
2)−n x2)
Code…
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c 2014 Russel Winder Printed for JAXLondon 2014 Workshop 2014-10-13 02–05

13. 05—Closing
Dataflow
The Forgotten Way
Dr Russel Winder
russel@winder.org.uk
@russel_winder
http://www.russel.org.uk
Copyright © 2014 Russel Winder 1
Closing
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c 2014 Russel Winder Printed for JAXLondon 2014 Workshop 2014-10-13 05–01

14. Event-based.
05—Closing
Channels
aka
Flows
Processes
Processes process when data is ready on the input
channels, putting data on the output channels.
Copyright © 2014 Russel Winder 3
Keep the data
flowing.
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c 2014 Russel Winder Printed for JAXLondon 2014 Workshop 2014-10-13 05–02