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Memory Management, C# 7.2 and Span<T>
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slang25
March 25, 2018
Technology
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Memory Management, C# 7.2 and Span<T>
A tour of .NET memory management, new C# features and Span
slang25
March 25, 2018
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Transcript
Memory Management, C# 7.2 and Span<T>
HELLO! F# |> I ❤ 9 years of experience in
.NET Organiser of Bristol F# meetup and DDD South West You can find me at @stuartblang & http://stuartlang.uk
None
Rust
• FAST • SAFE • MAINTAINABLE Can C# have all
3?
C# as a high performance language
C# as a high performance language
Performance where it matters Fram eworks Libraries
Always Measure
Measure with... ▸ Memory Performance Counters ▸ BenchmarkDotNet ▸ dotMemory
▸ Visual Studio
How it works
None
None
“ The Stack Is An Implementation Detail. - Eric Lippert
Part One Part Two
Types ▸ Value types ▹ Structs ▹ Enums ▹ Bool
▹ Int, Float, Short, Long… ▹ Byte ▸ Reference types ▹ Class ▹ Interface ▹ Array ▹ String ▹ Delegate
Code Stack a=42 Stack x(ref) Heap object: array{1,2,3} sharplab.io demo
Code - behaviour
Stack Credit: http://www.i-programmer.info/ebooks/deep-c/363
Heap Small Object Heap Large Object Heap Gen 0 Gen
1 Gen 2
Heap Credit: https://www.dynatrace.com/resources/ebooks/javabook/how-garbage-collection-works/
Great Resource ▸ http://benhall.io/a-super-simplified-exp lanation-of-net-garbage-collection/
Stack vs Heap What? Lifetime When disposed? Time to dispose
Stack Local values Local references (just the ref part) Stack frame Deterministic Constant (near instant) Heap Reference object instances Unrestricted GC non-deterministic It depends (non-trivial)
Watch out for hidden allocations ▸ Let’s see some examples
Watch out for hidden allocations
Watch out for hidden allocations
Watch out for hidden allocations
Watch out for hidden allocations
Plugins ▸ R# Heap Allocations Viewer ▸ Roslyn Clr Heap
Allocation Analyzer
None
In Parameters
In Parameters - cont. ▸ Essentially readonly ref ▸ Where
you want to want to pass by-ref for performance, with the safety and behaviour or by-value ▸ Watch out for copying with invoking methods on non-readonly structs
Ref extension methods
Ref locals ▸ Reference semantics with value types
Ref locals ▸ Can be thought of as aliases
Ref returns
Ref Struct ▸ Aka ref-like ▸ Stack-only! ▸ To support
Span<T>
Ref Struct
“ The great Eric Lippert once wrote “The Stack Is
An Implementation Detail”, and basically that’s not true anymore. - Jon Skeet
Span<T> ▸ Abstraction over arbitrary memory Span<T> Marshal.AllocHGlobal() stackalloc []
new []
Span<T>
Span<T>
Span<T> - Why stack-only? ▸ Safe lifetime - cannot outlive
stack memory ▸ Safe concurrency - No struct tearing ▸ It’s fast!
Span<T> - Other properties ▸ Efficient representation ▸ GC tracking
- refs will be maintained by GC
Use Cases ▸ Alternative to unsafe code ▸ Parsing text
▸ Sharing partial parts of memory
Problem with pointers ▸ Requires GC pinning (for heap memory)
▸ Mustn’t escape pointer (for stack) ▸ No bounds checking ▸ Unsafe code blocks
Problem with pointers
Credit: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/stackalloc
None
You can still pin
You can still pin - in C# 7.3
BenchmarkDotNet
None
None
Results
C# 8 - Slicing with Ranges demo
None
None
Span<T> Framework APIs netstandard2.0 ❌ netstandard2.1 ✅ Today Next netcoreapp2.1
✅ netcoreapp2.0 ❌ netcoreapp2.2 ✅ netcoreapp2.3 ✅ netcoreapp3.0 ✅ net472 ❌ net48 ❌ net49 ❓ ❓
Related topics ▸ ReadOnlySpan<T> ▸ Memory<T> & ReadOnlyMemory<T> ▸ System.Runtime.CompilerServices.Unsafe
▸ MemoryMarshal.AsBytes(span) ▸ MemoryMarshal.Cast<TFrom,TTo>(span)
Libraries using Span<T> (just some) ▸ Utf8Json ▸ SpanJson ▸
ZeroFormatter ▸ StackExchange.Redis
Case study JustEat.StatsD PRs Low hanging fruit: #55, #59, #63,
#65 Master class by dv00d00: #104 - Zero Allocations
Good Reads ▸ Adam Sitnik - Span ▸ Marc Gravell
- Spans and ref Parts 1 & 2 ▸ Span<T> spec ▸ Vladimir Sadov ▸ All About Span: Exploring a New .NET Mainstay - Stephen Toub ▸ Maarten Balliauw
Summary
THANKS! Any questions? You can find me at @stuartblang