I sometimes write C# in my day job. But I think I don't know much about how to write really fast C#. Do you have any recommendations for learning resources on that topic?
LINQ is fine (but enterprise style never is, yes), it’s a matter of scale and what kind of a domain the code is targeted too. C# needs to be approached a little like C++ and Rust in this regard. Having standard performance optimization knowledge helps greatly.
Also can recommend reading all the performance improvements blog posts by Stephen Toub as well as learning to understand disassembly at a basic level which .NET offers a few convenient tools to get access to.
Thank you. I once read a bit about Span<T>, but some of this reference stuff is very new to me. Interesting, definitely. C# really is a big language nowadays...
Spans are just a slice type, but those which any type based on contiguous memory can be coerced to (usually). I’m sure you’re already using them somewhere without realizing that. Their main use case in regular code is zero-cost slicing e.g. text.AsSpan(2..8).
It's a heavily gamed benchmark, but TechEmpower Fortunes is pretty good at revealing the max throughput of a language runtime for "specially tuned" code (instead of idiomatic code).
I judge more idiomatic / typical code complexity by the length of stack traces in production web app crashes. Enterprise Java apps can produce monstrous traces that are tens of pages long.
ASP.NET Core 9 is a bit worse than ASP.NET Web Forms used to be because of the increased flexibility and async capability, but it's still nowhere near as bad as a typical Java app.
What matters in practical scenarios is that ASP.NET Core is significantly faster than Spring Boot. If you have a team willing to use ActiveJ or Vert.x, you are just as likely have a team willing to customize their C# implementation to produce numbers just as good at web application tasks and much better at something lower level. There are also issues with TechEmpower that make it highly sensitive to specific HW/Kernel/Libraries combination in ways which alter the rankings significantly. .NET team hosts a farm to do their own TechEmpower runs and it just keeps regressing with each new version of Linux kernel (for all entries), despite CPU% going down and throughput improving in separate more isolated ASP.NET Core evaluations. Mind you, the architecture of ASP.NET Core + Kestrel, in my opinion, leaves some performance on the table, and I think Techempower is a decent demonstration of where you can expect the average framework performance to sit at once you start looking at specific popular options most teams use.
No, records are a reduction in boilerplate for regular classes (the result also happens to be read-only — not deeply immutable, mind you). Value types are in the works:
A few important ones:
- Avoid memory allocations as much as you can. That's a primary thing. For example, case insensitive string comparisons using "a.ToUpper() == b.ToUpper()" in a tight loop are a performance disaster, when "string.Equals(a, b, StringComparison.CurrentCultureIgnoreCase)" is readily available.
- Do not use string concatenation (which allocates), instead prefer StringBuilder,
- Generally remember than any string operation (such as extracting a substring) means allocation of a new string. Instead use methods that return Span over the original string, in case of mystr.Substring(4,6) it can be a.AsSpan(4,6),
- Beware of some combinations of Linq methods, such as "collection.Where(condition).First()" is faster than "collection.First(condition)" etc.
Apart from that (which simply concerns strings, as they're the great source of performance issues, all generic best practices, applicable to any language, should be followed.
There are plenty resources on the net, just search for it.
* Span<T>: https://learn.microsoft.com/en-us/archive/msdn-magazine/2018...
* C# now has a limited borrow checker-like mechanism to safely handle local references: https://em-tg.github.io/csborrow/
* Here is a series of articles on the topic: https://www.stevejgordon.co.uk/writing-high-performance-csha...
* In general, avoid enterprise style C# (ie., lots of class and design patterns) and features like LINQ which allocate a lot of temporaries.