Sean Kenney - Solving Parallel Software Challenges with Patterns

© Copyright 2012 Avanade Inc. All Rights Reserved. Confidential For Internal Use Only
No. 2

No. 3

No. 4
Architect Developer Tester
Product
Management
Business
Management

No. 5
Most servers
today both have
multi-core and
multi-processor
architecture
You should not
rely on the OS to
do parallel
programming
Parallel
programming is
just not for Super
Geeks any more
(Driver
developers, OS
developers, C++
guys)
All verticals are
starting to
want/need
parallel
programming
Parallel
programming can
be leveraged well
in some cloud
scenarios

Beijing National Stadium - a.k.a “Bird’s Nest”

Concurrency
• GOAL: Prevent thread starvation
• concept related to multitasking and asynchronous input-output (I/O)
• existence of multiple threads of execution that may each get a slice of
time to execute before being preempted by another thread
Parallelism
• GOAL: Maximize processor usage across all available cores
• concurrent threads execute at the same time across cores
• focuses on improving the performance of applications that use a lot
of processor power and are not constantly interrupted when multiple
cores are available.

No. 9

TPL for .net
MPL Express/JFFP
RiverTrail for Javascript

Decomposition Coordination
Scalable
Sharing

No. 12
• Too fine = overhead to manage will become to much
• Too course = parallel opportunities will be lost
Identify tasks at a level of granularity that results in
efficient use of hardware resources.
• They should remain independent of each other, and have enough tasks to
keep the cores busy
Tasks should be as large as possible
• Dedicate some time to understand these components.
Decomposing a problem into tasks requires a good
understanding of the algorithmic and structural aspects
of your application.

Sean’s General Rule of thumb:
If iteration takes longer than 1 minute, review further.

No. 14
Coordination depends on
specifically which parallel
patterns you use to
implement
Application algorithms are
constrained by order of
execution and degree of
parallelism
• Constraints can come from data
flow or control flow.
The Futures pattern uses
Continuation to manage
coordination.
• Make sure that you understand any
coordination, before modifying you
application.
Mapping out dependencies
in a graph or inheritance
tree helps truly understand
the landscape

No. 15
Limit your
shared
variables
Use immutable
data when you
can Introduce new steps in
your algorithm that merge
local versions of mutable
state at checkpoints
Adding synchronization
reduces the parallelism of
your application.

Parallel Loop
Parallel Tasks
Parallel Aggregation
Futures
Pipelines

No. 17
Do you have sequential loops where there's no
communication among the steps of each
iteration?
Use the Parallel Loop pattern

Parallel loops apply an independent operation to
multiple inputs simultaneously.
Very similar to for and foreach.
Sequence in the collection will not matter.
Do not replace all for and for each loops with the
parallel equivalent. You will get into trouble

No – array cannot be divided into parts that can be sorted independently.
No, because the sum of the entire collection is needed, not the sums of
separate parts.
Yes, because each slide can be considered independently.

No. 21
Do you have distinct operations with well-
defined control dependencies and are these
operations largely free of serializing
dependencies?
Use the Parallel Task pattern

• Sometimes referred to as Fork/Join pattern or the
Master/Worker pattern.
Parallel Tasks allow you to establish parallel
control flow in the style of fork and join.
• Don’t assume that all parallel tasks will immediately run. That is
up to the scheduler.
You can wait for a single task or multiple tasks.

No. 24
Do you need to summarize data by applying some
kind of combination operator? Do you have loops
with steps that are not fully independent?
Use the Parallel Aggregation pattern

Introduces special steps in the algorithm for
merging partial results.
This pattern expresses a reduction operation and
includes map/reduce as one of its variations
Uses unshared, local variables that are merged at
the end of the computation to give the final
result
a.k.a. as The Parallel Reduction pattern because it
combines multiple inputs into a single output

No. 28
Does the ordering of steps in your algorithm
depend on data flow constraints?
Use the Futures pattern

Makes the data flow dependencies between tasks
explicit.
A future is a stand-in for a computational result
that is initially unknown but becomes known
The Futures pattern integrates task parallelism
with the familiar world of arguments and return
values
If a task in the chain is depending on another to
finish, it will block. The core will be available for
other tasks.
a.k.a Task Graph pattern.

No. 30
F1 F2
F3
F4
F5
F6
F1
F2
F3
F4
F5
F6
Method Chain Method Chain using Futures

No. 32
Does your application perform a sequence of
operations repetitively? Does the order of
processing matter?
Use the Pipeline pattern

Pipelines consist of components that are
connected by queues, in the style of producers
and consumers.
All the components run in parallel even though
the order of inputs is respected.
Analogous to assembly lines in a factory
Pipelines allow you to use parallelism in cases
where there are too many dependencies to use a
parallel loop

No. 34

Concurrency Visualizer
Debugging
Parallel Stacks Windows
Parallel Tasks Windows

• Parallel Programming is expected in most software
• Clearly understand the core design aspects
• Decomposition
• Coordination
• Scalable Sharing
• Get to know the 5 key parallel patterns
• Parallel Loop
• Parallel Tasks
• Parallel Aggregation
• Futures
• Pipelines
• Leverage industry tooling to make you experience
easier.

Sean Kenney - Solving Parallel Software Challenges with Patterns

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