Russel Winder is an expert presenter on concurrency and parallelism who has spoken at previous JAX London conferences. The document discusses the history of concurrency from single-CPU single-program computing to modern multi-CPU multi-task systems. It also covers the evolution of Java features from early threads and locks to more modern approaches like lambda expressions, streams, and CompletableFuture that abstract away concurrency details. The presentation examines different parallel computing approaches like pipelines, actors, and data parallelism.

1. Copyright © 2018 Russel Winder 1
On Concurrency and Parallelism
in the JVMVerse
Russel Winder
@russel_winder
russel@winder.org.uk
https://www.russel.org.uk

2. Copyright © 2018 Russel Winder 2
The Presenter
● Ex theoretical physicist
● Ex UNIX systems programmer
●
Ex academic:
– Parallel programming
– Software development and programming
– HCI, UI, UX
● Ex Company director
● Ex Independent consultant
● Ex analyst
● Ex author
● Ex expert witness
● Ex trainer
Russel Winder

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Me at Previous JAXLondons
● 2011
”Just Keep Passing the
Messages”
● 2012
”it’S All About Processes
Communicating”
Also many sessions at other conferences

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Concurrency
●
dictionary.com – concurrence
– the act of concurring.
– accordance in opinion; agreement:
With the concurrence of several
specialists, our doctor
recommended surgery.
– cooperation, as of agents or
causes; combined action or effort.
● Wikipedia – concurrency
– In computer science,
concurrency refers to the ability
of different parts or units of a
program, algorithm, or problem to
be executed out-of-order or in
partial order, without affecting
the final outcome.

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Parallelism
● dictionary.com – parallelism
– the position or relation of
parallels.
– agreement in direction, tendency,
or character; the state or
condition of being parallel.
– a parallel or comparison.
● Wikipedia – parallelism
– Parallel computing is a type
of computation in which
many calculations or the
execution of processes are
carried out simultaneously.

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Original computing:
single CPU, single program

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Multitasking: single CPU, many programs

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Five programs, one CPU

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OS manages all the programs in one memory,
eventually get virtual memory, in the mean time locks,
semaphores, monitors, mutexes, and the theory of
concurrency get invented.

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Five programs, one CPU

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Five programs, four CPUs

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Moving from operating systems
to applications

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One program, one task, one CPU

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One program, four tasks, one CPU

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One program, four tasks, four CPUs

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One program, four tasks, four CPUs

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Locks, mutexes, sempahores, monitors
are the enemy of parallelism

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What is the problem…

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Shared Memory

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A Bit of Java History
● 1995 — Java introduces threads, multithreading, monitors,
synchronized, locks, etc.
● 1996 — People predict lots of tears and grief.
● 2002 —Doug Lea gets JSR166 moving.
● 2011 — Fork/Join framework in Java 7.

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A Bit More Java History
● 2014 — Java 8 introduces:
– Lambda Expressions,
– Streams, and
– CompletableFuture.

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Abstract code away from the details of
managing concurrency and parallelism.

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Pipeline

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Dataflow

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Actors

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Distributed System

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Microservices

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Independent processes/tasks/programs
communicating by message passing

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Data Parallel

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Event Processing

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One program, four tasks

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Have we seen the code yet?

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Summary
● Gpars (Groovy)
● Quasar
● Kotlin Coroutines
Can Java catch up (again).

35. Copyright © 2018 Russel Winder 35
On Concurrency and Parallelism
in the JVMVerse
Russel Winder
@russel_winder
russel@winder.org.uk
https://www.russel.org.uk