book

Optimized C++

Name: Optimized C++
Author: Kurt Guntheroth
ISBN: 9781491922019

by Kurt Guntheroth

April 2016

Intermediate to advanced

388 pages

11h 5m

English

O'Reilly Media, Inc.

Read now

Unlock full access

Preface
Apology for the Code in This BookUsing Code ExamplesConventions Used in This Book
1. An Overview of Optimization
Optimization Is Part of Software DevelopmentOptimization Is EffectiveIt’s OK to OptimizeA Nanosecond Here, a Nanosecond ThereSummary of Strategies for Optimizing C++ CodeUse a Better Compiler, Use Your Compiler BetterUse Better AlgorithmsUse Better LibrariesReduce Memory Allocation and CopyingRemove ComputationUse Better Data StructuresIncrease ConcurrencyOptimize Memory ManagementSummary
2. Computer Behavior Affecting Optimization
Lies C++ Believes About ComputersThe Truth About ComputersMemory Is SlowMemory Is Not Accessed in BytesSome Memory Accesses Are Slower than OthersMemory Words Have a Big End and a Little EndMemory Has Finite CapacityInstruction Execution Is SlowMaking Decisions Is Hard for ComputersThere Are Multiple Streams of Program ExecutionCalling into the Operating System Is ExpensiveC++ Tells Lies TooAll Statements Are Not Equally ExpensiveStatements Are Not Executed in OrderSummary
3. Measure Performance
The Optimizing MindsetPerformance Must Be MeasuredOptimizers Are Big Game HuntersThe 90/10 RuleAmdahl’s LawPerform ExperimentsKeep a Lab NotebookMeasure Baseline Performance and Set GoalsYou Can Improve Only What You MeasureProfile Program ExecutionTime Long-Running Code“A Little Learning” About Measuring TimeMeasuring Time with ComputersOvercoming Measurement ObstaclesCreate a Stopwatch ClassTime Hot Functions in a Test HarnessEstimate Code Cost to Find Hot CodeEstimate the Cost of Individual C++ StatementsEstimate the Cost of LoopsOther Ways to Find Hot SpotsSummary
4. Optimize String Use: A Case Study
Why Strings Are a ProblemStrings Are Dynamically AllocatedStrings Are ValuesStrings Do a Lot of CopyingFirst Attempt at Optimizing StringsUse Mutating String Operations to Eliminate TemporariesReduce Reallocation by Reserving StorageEliminate Copying of String ArgumentsEliminate Pointer Dereference Using IteratorsEliminate Copying of Returned String ValuesUse Character Arrays Instead of StringsSummary of First Optimization AttemptSecond Attempt at Optimizing StringsUse a Better AlgorithmUse a Better CompilerUse a Better String LibraryUse a Better AllocatorEliminate String ConversionConversion from C String to std::stringConverting Between Character EncodingsSummary
5. Optimize Algorithms
Time Cost of AlgorithmsBest-Case, Average, and Worst-Case Time CostAmortized Time CostOther CostsToolkit to Optimize Searching and SortingEfficient Search AlgorithmsTime Cost of Searching AlgorithmsAll Searches Are Equal When n Is SmallEfficient Sort AlgorithmsTime Cost of Sorting AlgorithmsReplace Sorts Having Poor Worst-Case PerformanceExploit Known Properties of the Input DataOptimization PatternsPrecomputationLazy ComputationBatchingCachingSpecializationTaking Bigger BitesHintingOptimizing the Expected PathHashingDouble-CheckingSummary
6. Optimize Dynamically Allocated Variables
C++ Variables RefresherStorage Duration of VariablesOwnership of VariablesValue Objects and Entity ObjectsC++ Dynamic Variable API RefresherSmart Pointers Automate Ownership of Dynamic VariablesDynamic Variables Have Runtime CostReduce Use of Dynamic VariablesCreate Class Instances StaticallyUse Static Data StructuresUse std::make_shared Instead of newDon’t Share Ownership UnnecessarilyUse a “Master Pointer” to Own Dynamic VariablesReduce Reallocation of Dynamic VariablesPreallocate Dynamic Variables to Prevent ReallocationCreate Dynamic Variables Outside of LoopsEliminate Unneeded CopyingDisable Unwanted Copying in the Class DefinitionEliminate Copying on Function CallEliminate Copying on Function ReturnCopy Free LibrariesImplement the “Copy on Write” IdiomSlice Data StructuresImplement Move SemanticsNonstandard Copy Semantics: A Painful Hackstd::swap(): The Poor Man’s Move SemanticsShared Ownership of EntitiesThe Moving Parts of Move SemanticsUpdate Code to Use Move SemanticsSubtleties of Move SemanticsFlatten Data StructuresSummary
7. Optimize Hot Statements
Remove Code from LoopsCache the Loop End ValueUse More Efficient Loop StatementsCount Down Instead of UpRemove Invariant Code from LoopsRemove Unneeded Function Calls from LoopsRemove Hidden Function Calls from LoopsRemove Expensive, Slow-Changing Calls from LoopsPush Loops Down into Functions to Reduce Call OverheadDo Some Actions Less FrequentlyWhat About Everything Else?Remove Code from FunctionsCost of Function CallsDeclare Brief Functions InlineDefine Functions Before First UseEliminate Unused PolymorphismDiscard Unused InterfacesSelect Implementation at Compile Time with TemplatesEliminate Uses of the PIMPL IdiomEliminate Calls into DLLsUse Static Member Functions Instead of Member FunctionsMove Virtual Destructor to Base ClassOptimize ExpressionsSimplify ExpressionsGroup Constants TogetherUse Less-Expensive OperatorsUse Integer Arithmetic Instead of Floating ArithmeticDouble May Be Faster than FloatReplace Iterative Computations with Closed FormsOptimize Control Flow IdiomsUse switch Instead of if-elseif-elseUse Virtual Functions Instead of switch or ifUse No-Cost Exception HandlingSummary
8. Use Better Libraries
Optimize Standard Library UsePhilosophy of the C++ Standard LibraryIssues in Use of the C++ Standard LibraryOptimize Existing LibrariesChange as Little as PossibleAdd Functions Rather than Change FunctionalityDesign Optimized LibrariesCode in Haste, Repent at LeisureParsimony Is a Virtue in Library DesignMake Memory Allocation Decisions Outside the LibraryWhen in Doubt, Code Libraries for SpeedFunctions Are Easier to Optimize than FrameworksFlatten Inheritance HierarchiesFlatten Calling ChainsFlatten Layered DesignsAvoid Dynamic LookupBeware of ‘God Functions’Summary
9. Optimize Searching and Sorting
Key/Value Tables Using std::map and std::stringToolkit to Improve Search PerformanceMake a Baseline MeasurementIdentify the Activity to Be OptimizedDecompose the Activity to Be OptimizedChange or Replace Algorithms and Data StructuresUsing the Optimization Process on Custom AbstractionsOptimize Search Using std::mapUse Fixed-Size Character Array Keys with std::mapUse C-Style String Keys with std::mapUsing Map’s Cousin std::set When the Key Is in the ValueOptimize Search Using the <algorithm> HeaderKey/Value Table for Search in Sequence Containersstd::find(): Obvious Name, O(n) Time Coststd::binary_search(): Does Not Return ValuesBinary Search Using std::equal_range()Binary Search Using std::lower_bound()Handcoded Binary SearchHandcoded Binary Search using strcmp()Optimize Search in Hashed Key/Value TablesHashing with a std::unordered_mapHashing with Fixed Character Array KeysHashing with Null-Terminated String KeysHashing with a Custom Hash TableStepanov’s Abstraction PenaltyOptimize Sorting with the C++ Standard LibrarySummary

10. Optimize Data Structures
Get to Know the Standard Library ContainersSequence ContainersAssociative ContainersExperimenting with the Standard Library Containersstd::vector and std::stringPerformance Consequences of ReallocationInserting and Deleting in std::vectorIterating in std::vectorSorting std::vectorLookup with std::vectorstd::dequeInserting and Deleting in std::dequeIterating in std::dequeSorting std::dequeLookup with std::dequestd::listInserting and Deleting in std::listIterating in std::listSorting std::listLookup with std::liststd::forward_listInserting and Deleting in std::forward_listIterating in std::forward_listSorting std::forward_listLookup in std::forward_liststd::map and std::multimapInserting and Deleting in std::mapIterating in std::mapSorting std::mapLookup with std::mapstd::set and std::multisetstd::unordered_map and std::unordered_multimapInserting and Deleting in std::unordered_mapIterating in std::unordered_mapLookup with std::unordered_mapOther Data StructuresSummary
11. Optimize I/O
A Recipe for Reading FilesCreate a Parsimonious Function SignatureShorten Calling ChainsReduce ReallocationTake Bigger Bites—Use a Bigger Input BufferTake Bigger Bites—Read a Line at a TimeShorten Calling Chains AgainThings That Didn’t HelpWriting FilesReading from std::cin and Writing to std::coutSummary
12. Optimize Concurrency
Concurrency RefresherA Walk Through the Concurrency ZooInterleaved ExecutionSequential ConsistencyRacesSynchronizationAtomicityC++ Concurrency Facilities RefresherThreadsPromises and FuturesAsynchronous TasksMutexesLocksCondition VariablesAtomic Operations on Shared VariablesOn Deck: Future C++ Concurrency FeaturesOptimize Threaded C++ ProgramsPrefer std::async to std::threadCreate as Many Runnable Threads as CoresImplement a Task Queue and Thread PoolPerform I/O in a Separate ThreadProgram Without SynchronizationRemove Code from Startup and ShutdownMake Synchronization More EfficientReduce the Scope of Critical SectionsLimit the Number of Concurrent ThreadsAvoid the Thundering HerdAvoid Lock ConvoysReduce ContentionDon’t Busy-Wait on a Single-Core SystemDon’t Wait ForeverRolling Your Own Mutex May Be IneffectiveLimit Producer Output Queue LengthConcurrency LibrariesSummary
13. Optimize Memory Management
C++ Memory Management API RefresherThe Life Cycle of Dynamic VariablesMemory Management Functions Allocate and Free MemoryNew-Expressions Construct Dynamic VariablesDelete-Expressions Dispose of Dynamic VariablesExplicit Destructor Calls Destroy Dynamic VariablesHigh-Performance Memory ManagersProvide Class-Specific Memory ManagersFixed-Size-Block Memory ManagerBlock ArenaAdding a Class-Specific operator new()Performance of the Fixed-Block Memory ManagerVariations on the Fixed-Block Memory ManagerNon-Thread Safe Memory Managers Are EfficientProvide Custom Standard Library AllocatorsMinimal C++11 AllocatorAdditional Definitions for C++98 AllocatorA Fixed-Block AllocatorA Fixed-Block Allocator for StringsSummary
Index

Content preview from Optimized C++

Chapter 2. Computer Behavior Affecting Optimization

Lying, the telling of beautiful untrue things, is the proper aim of Art.

Oscar Wilde, “The Decay of Lying,” Intentions (1891)

The purpose of this chapter is to provide the bare minimum of background information about computer hardware to motivate the optimizations described in this book, to prevent readers going mad poring over 600-page processor handbooks. It takes a superficial look at processor architecture to extract some heuristics to guide optimization efforts. The very impatient reader might skip this chapter for now and return when other chapters refer to it, though the information here is important and useful.

Microprocessor devices in current use are incredibly diverse. They range from sub-$1 embedded devices with just a few thousand gates and clock rates below 1 MHz to desktop-class devices with billions of gates and gigahertz clocks. Mainframe computers can be the size of a large room, containing thousands of independent execution units and drawing enough electrical power to light a small city. It is tempting to believe that nothing connects this profusion of computing devices that would lead to usable generalizations. In reality, though, they have useful similarities. After all, if there were no similarities, it would not be possible to compile C++ code for the many processors for which there are compilers.

All computers in wide use execute instructions stored in memory. The instructions act upon data that is also ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.

Read now

Unlock full access

More than 5,000 organizations count on O’Reilly

O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.

Julian F.

Head of Cybersecurity

I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.

Addison B.

Field Engineer

I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.

Amir M.

Data Platform Tech Lead

I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.

Mark W.

Embedded Software Engineer

Publisher Resources

ISBN: 9781491922057Errata Page

Cloud Computing

Data Engineering

Data Science

AI & ML

Programming Languages

Software Architecture

IT/Ops

Security

Design

Business

Soft Skills

Optimized C++

by Kurt Guntheroth

Chapter 2. Computer Behavior Affecting Optimization

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.