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
   

   View Slide

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
   

   View Slide

3. View Slide

4. Rust
   

   View Slide

5. ● FAST
   ● SAFE
   ● MAINTAINABLE
   Can C# have all 3?
   

   View Slide

6. C# as a high performance language
   

   View Slide

7. C# as a high performance language
   

   View Slide

8. Performance where it matters
   Fram
   eworks
   Libraries
   

   View Slide

9. Always
   Measure
   

   View Slide

10. Measure with...
    ▸ Memory Performance Counters
    ▸ BenchmarkDotNet
    ▸ dotMemory
    ▸ Visual Studio
    

    View Slide

11. How it
    works
    

    View Slide

12. View Slide

13. View Slide

14. “
    The Stack Is An Implementation Detail.
    - Eric Lippert
    Part One
    Part Two
    

    View Slide

15. Types
    ▸ Value types
    ▹ Structs
    ▹ Enums
    ▹ Bool
    ▹ Int, Float, Short, Long…
    ▹ Byte
    ▸ Reference types
    ▹ Class
    ▹ Interface
    ▹ Array
    ▹ String
    ▹ Delegate
    

    View Slide

16. Code
    Stack
    a=42
    Stack
    x(ref)
    Heap
    object:
    array{1,2,3}
    sharplab.io demo
    

    View Slide

17. Code - behaviour
    

    View Slide

18. Stack
    Credit: http://www.i-programmer.info/ebooks/deep-c/363
    

    View Slide

19. Heap
    Small Object Heap Large Object Heap
    Gen 0 Gen 1 Gen 2
    

    View Slide

20. Heap
    Credit:
    https://www.dynatrace.com/resources/ebooks/javabook/how-garbage-collection-works/
    

    View Slide

21. Great Resource
    ▸ http://benhall.io/a-super-simplified-exp
    lanation-of-net-garbage-collection/
    

    View Slide

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)
    

    View Slide

23. Watch out for hidden allocations
    ▸ Let’s see some examples
    

    View Slide

24. Watch out for hidden allocations
    

    View Slide

25. Watch out for hidden allocations
    

    View Slide

26. Watch out for hidden allocations
    

    View Slide

27. Watch out for hidden allocations
    

    View Slide

28. Plugins
    ▸ R# Heap Allocations Viewer
    ▸ Roslyn Clr Heap Allocation Analyzer
    

    View Slide

29. View Slide

30. In Parameters
    

    View Slide

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
    

    View Slide

32. Ref extension methods
    

    View Slide

33. Ref locals
    ▸ Reference semantics with value types
    

    View Slide

34. Ref locals
    ▸ Can be thought of as aliases
    

    View Slide

35. Ref returns
    

    View Slide

36. Ref Struct
    ▸ Aka ref-like
    ▸ Stack-only!
    ▸ To support Span
    

    View Slide

37. Ref Struct
    

    View Slide

38. “
    The great Eric Lippert once wrote
    “The Stack Is An Implementation
    Detail”, and basically that’s not
    true anymore.
    - Jon Skeet
    

    View Slide

39. Span
    ▸ Abstraction over arbitrary memory
    Span
    Marshal.AllocHGlobal() stackalloc [] new []
    

    View Slide

40. Span
    

    View Slide

41. Span
    

    View Slide

42. Span - Why stack-only?
    ▸ Safe lifetime - cannot outlive stack memory
    ▸ Safe concurrency - No struct tearing
    ▸ It’s fast!
    

    View Slide

43. Span - Other properties
    ▸ Efficient representation
    ▸ GC tracking - refs will be maintained by GC
    

    View Slide

44. Use Cases
    ▸ Alternative to unsafe code
    ▸ Parsing text
    ▸ Sharing partial parts of memory
    

    View Slide

45. Problem with pointers
    ▸ Requires GC pinning (for heap memory)
    ▸ Mustn’t escape pointer (for stack)
    ▸ No bounds checking
    ▸ Unsafe code blocks
    

    View Slide

46. Problem with pointers
    

    View Slide

47. Credit: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/stackalloc
    

    View Slide

48. View Slide

49. You can still pin
    

    View Slide

50. You can still pin - in C# 7.3
    

    View Slide

51. BenchmarkDotNet
    

    View Slide

52. View Slide

53. View Slide

54. Results
    

    View Slide

55. C# 8 - Slicing with Ranges
    demo
    

    View Slide

56. View Slide

57. View Slide

58. Span Framework APIs
    netstandard2.0 ❌ netstandard2.1 ✅
    Today Next
    netcoreapp2.1 ✅
    netcoreapp2.0 ❌
    netcoreapp2.2 ✅
    netcoreapp2.3 ✅
    netcoreapp3.0 ✅
    net472 ❌ net48 ❌ net49 ❓
    ❓
    

    View Slide

59. Related topics
    ▸ ReadOnlySpan
    ▸ Memory & ReadOnlyMemory
    ▸ System.Runtime.CompilerServices.Unsafe
    ▸ MemoryMarshal.AsBytes(span)
    ▸ MemoryMarshal.Cast(span)
    

    View Slide

60. Libraries using Span (just some)
    ▸ Utf8Json
    ▸ SpanJson
    ▸ ZeroFormatter
    ▸ StackExchange.Redis
    

    View Slide

61. Case study
    JustEat.StatsD PRs
    Low hanging fruit:
    #55, #59, #63, #65
    Master class by dv00d00:
    #104 - Zero Allocations
    

    View Slide

62. Good Reads
    ▸ Adam Sitnik - Span
    ▸ Marc Gravell - Spans and ref Parts 1 & 2
    ▸ Span spec
    ▸ Vladimir Sadov
    ▸ All About Span: Exploring a New .NET Mainstay -
    Stephen Toub
    ▸ Maarten Balliauw
    

    View Slide

63. Summary
    

    View Slide

64. THANKS!
    Any questions?
    You can find me at @stuartblang
    

    View Slide