Memory Management, C# 7.2 and Span<T>

A tour of .NET memory management, new C# features and Span

Transcript

1. Memory Management, C# 7.2 and Span<T>
2. 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
4. Rust
5. • FAST • SAFE • MAINTAINABLE Can C# have all 3?
6. C# as a high performance language
7. C# as a high performance language
8. Performance where it matters Fram eworks Libraries
9. Always Measure
10. Measure with... ▸ Memory Performance Counters ▸ BenchmarkDotNet ▸ dotMemory ▸ Visual Studio
11. How it works
14. “ The Stack Is An Implementation Detail. - Eric Lippert Part One Part Two
15. Types ▸ Value types ▹ Structs ▹ Enums ▹ Bool ▹ Int, Float, Short, Long… ▹ Byte ▸ Reference types ▹ Class ▹ Interface ▹ Array ▹ String ▹ Delegate
16. Code Stack a=42 Stack x(ref) Heap object: array{1,2,3} sharplab.io demo
17. Code - behaviour
18. Stack Credit: http://www.i-programmer.info/ebooks/deep-c/363
19. Heap Small Object Heap Large Object Heap Gen 0 Gen 1 Gen 2
20. Heap Credit: https://www.dynatrace.com/resources/ebooks/javabook/how-garbage-collection-works/
21. Great Resource ▸ http://benhall.io/a-super-simplified-exp lanation-of-net-garbage-collection/
22. 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)
23. Watch out for hidden allocations ▸ Let’s see some examples
24. Watch out for hidden allocations
25. Watch out for hidden allocations
26. Watch out for hidden allocations
27. Watch out for hidden allocations
28. Plugins ▸ R# Heap Allocations Viewer ▸ Roslyn Clr Heap Allocation Analyzer
30. In Parameters
31. 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
32. Ref extension methods
33. Ref locals ▸ Reference semantics with value types
34. Ref locals ▸ Can be thought of as aliases
35. Ref returns
36. Ref Struct ▸ Aka ref-like ▸ Stack-only! ▸ To support Span<T>
37. Ref Struct
38. “ The great Eric Lippert once wrote “The Stack Is An Implementation Detail”, and basically that’s not true anymore. - Jon Skeet
39. Span<T> ▸ Abstraction over arbitrary memory Span<T> Marshal.AllocHGlobal() stackalloc [] new []
40. Span<T>
41. Span<T>
42. Span<T> - Why stack-only? ▸ Safe lifetime - cannot outlive stack memory ▸ Safe concurrency - No struct tearing ▸ It’s fast!
43. Span<T> - Other properties ▸ Efficient representation ▸ GC tracking - refs will be maintained by GC
44. Use Cases ▸ Alternative to unsafe code ▸ Parsing text ▸ Sharing partial parts of memory
45. Problem with pointers ▸ Requires GC pinning (for heap memory) ▸ Mustn’t escape pointer (for stack) ▸ No bounds checking ▸ Unsafe code blocks
46. Problem with pointers
47. Credit: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/stackalloc
49. You can still pin
50. You can still pin - in C# 7.3
51. BenchmarkDotNet
54. Results
55. C# 8 - Slicing with Ranges demo
58. Span<T> Framework APIs netstandard2.0 ❌ netstandard2.1 ✅ Today Next netcoreapp2.1 ✅ netcoreapp2.0 ❌ netcoreapp2.2 ✅ netcoreapp2.3 ✅ netcoreapp3.0 ✅ net472 ❌ net48 ❌ net49 ❓ ❓
59. Related topics ▸ ReadOnlySpan<T> ▸ Memory<T> & ReadOnlyMemory<T> ▸ System.Runtime.CompilerServices.Unsafe ▸ MemoryMarshal.AsBytes(span) ▸ MemoryMarshal.Cast<TFrom,TTo>(span)
60. Libraries using Span<T> (just some) ▸ Utf8Json ▸ SpanJson ▸ ZeroFormatter ▸ StackExchange.Redis
61. Case study JustEat.StatsD PRs Low hanging fruit: #55, #59, #63, #65 Master class by dv00d00: #104 - Zero Allocations
62. 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
63. Summary
64. THANKS! Any questions? You can find me at @stuartblang