5. Parallelize for Performance | Haskell High Performance Programming

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Haskell High Performance Programming

By : Thomasson

3 (2)

Haskell High Performance Programming

3 (2)

By: Thomasson

Overview of this book

Haskell, with its power to optimize the code and its high performance, is a natural candidate for high performance programming. It is especially well suited to stacking abstractions high with a relatively low performance cost. This book addresses the challenges of writing efficient code with lazy evaluation and techniques often used to optimize the performance of Haskell programs. We open with an in-depth look at the evaluation of Haskell expressions and discuss optimization and benchmarking. You will learn to use parallelism and we'll explore the concept of streaming. We’ll demonstrate the benefits of running multithreaded and concurrent applications. Next we’ll guide you through various profiling tools that will help you identify performance issues in your program. We’ll end our journey by looking at GPGPU, Cloud and Functional Reactive Programming in Haskell. At the very end there is a catalogue of robust library recommendations with code samples. By the end of the book, you will be able to boost the performance of any app and prepare it to stand up to real-world punishment.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

1. Identifying Bottlenecks

1. Identifying Bottlenecks

Meeting lazy evaluation

Memoization and CAFs

Recursion and accumulators

Inspecting time and space usage

Compiler code optimizations

Summary

2. Choosing the Correct Data Structures

2. Choosing the Correct Data Structures

Annotating strictness and unpacking datatype fields

Handling numerical data

Handling binary and textual data

Handling sequential data

Handling tabular data

Handling sparse data

Ephemeral data structures

Working with monads and monad stacks

Summary

3. Profile and Benchmark to Your Heart's Content

3. Profile and Benchmark to Your Heart's Content

Profiling time and allocations

Heap profiling

Benchmarking using the criterion library

Profile and monitor in real time

Summary

4. The Devil's in the Detail

4. The Devil's in the Detail

The anatomy of a Haskell project

Erroring and handling exceptions

Writing tests for Haskell

Trivia at term-level

Trivia at type-level

Useful GHC extensions

Summary

5. Parallelize for Performance

5. Parallelize for Performance

Primitive parallelism and the Runtime System

The Eval monad and strategies

The Par monad and schedules

Diagnosing parallelism – ThreadScope

Data parallel programming – Repa

Summary

6. I/O and Streaming

6. I/O and Streaming

Reading, writing, and handling resources

Streaming with side-effects

Logging in Haskell

Summary

7. Concurrency and Performance

7. Concurrency and Performance

Threads and concurrency primitives

Software Transactional Memory

Runtime System and threads

Asynchronous processing

Lifting up from I/O

Summary

8. Tweaking the Compiler and Runtime System (GHC)

8. Tweaking the Compiler and Runtime System (GHC)

Using GHC like a pro

Tuning GHC's Runtime System

Summary of useful GHC options

Summary of useful RTS options

Summary

9. GHC Internals and Code Generation

9. GHC Internals and Code Generation

Interpreting GHC's internal representations

Primitive GHC-specific features

Datatype generic programming

Generating Haskell with Haskell

Summary

10. Foreign Function Interface

10. Foreign Function Interface

From Haskell to C and C to Haskell

Data marshal and stable pointers

Summary

11. Programming for the GPU with Accelerate

11. Programming for the GPU with Accelerate

Writing Accelerate programs

Running with the CUDA backend

More Accelerate concepts

Summary

12. Scaling to the Cloud with Cloud Haskell

12. Scaling to the Cloud with Cloud Haskell

Processes and message-passing

Handling failure

Nodes and networking

Summary

13. Functional Reactive Programming

13. Functional Reactive Programming

The tiny discrete-time Elerea

Events and signal functions with Yampa

Reactive-banana – Safe and simple semantics

Combining events and behaviors

Summary

14. Library Recommendations

14. Library Recommendations

Representing data

Functional graphs

Numeric data for special use

Encoding and serialization

Persistent storage, SQL, and NoSQL

Networking and HTTP

Cryptography

Web technologies

Parsing and pretty-printing

Pretty-printing and text formatting

Control and utility libraries

Working with monads and transformers

Handling exceptions

Random number generators

Parallel and concurrent programming

Functional Reactive Programming

Mathematics, statistics, and science

Tools for research and sketching

The HaskellR project

Creating charts and diagrams

Scripting and CLI applications

Testing and benchmarking

Summary

Index

Index

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Primitive parallelism and the Runtime System

In Haskell, parallel execution (of pure values) boils down to evaluating thunks into WHNF simultaneously. The GHC primitive we can use to annotate parallelism is called par, exported from the Control.Parallel module in the parallel package:

par :: a → b → b

Note that par has exactly the same type as seq, which is used to control strictness. So whereas a `seq` b ensures that a is evaluated when b is evaluated, a `par` b evaluates a in parallel with b.

Let's start with a simple example. Everyone's favorite naive Fibonacci function appears again. This time, however, we will be calculating multiple Fibonacci numbers simultaneously. The following program prints Fibonacci numbers between 37 and 40:

-- file: fib.hs
fib :: Int -> Int
fib n
  | n <= 1 = 1
  | otherwise = let a = fib (n - 1)
                    b = fib (n - 2)
                    in a + b

main = print $
  let x = fib 37
      y = fib 38
      z = fib 39
      w = fib 40
      in (x,y...

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