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0 pointsnemothekid3y ago0 comments

I don't know much about the C# garbage collector; and it's likely that garbage collectors are a bad fit for programs that have hard deadlines.

That said, it could also be a function of the same "problem" Java has in its design - Java by default boxes everything and so every memory allocation increases garbage collection pressure. Go, by using escape analysis and favoring stack allocations, doesn't have this problem and has had sub-millisecond pauses for years now.

You rarely hear people complain about Go's GC despite it being much less mature than the JVMs. But due to actual language design, Go's GC does much less work. I wouldn't say “GC used to be bad but now it’s good”, but that "the design of languages like C# and Java were too dependent on using the GC for memory allocations, and there are other GC languaged out there that utilize the GC less which can lead to greater performance"

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rdw3y ago

You're right, and it's got more layers than that. C# does have value types, which are not boxed, and using them judiciously can avoid garbage. However, they are a more recent addition to the language (which started as a lame Java clone), and so the standard library tends to not know about them. Really trivial operations will allocate hundreds of bytes of garbage for no good reason. Example: iterating over a Dictionary. Or, IIRC, getting the current time. They've been cleaning up these functions to not create garbage over tiem, of course, but it's never fast enough for my taste and leads to some truly awful workarounds.

wesnerm23y ago

C# had value types and pointers from the very beginning. These are not a recent addition. The standard library does know about them. However, not until C# 2.0, which introduced generics, were collections able to avoid boxing value types.

There are some cases where allocations are made when they could have been avoided. Iterating over a dictionary creates a single IEnumerator object. Async methods, tuples, delegates, and lambda expressions also allocate memory as do literal strings. It is possible to have struct-based iterators and disposers. There are some recently added mitigations such as a ValueTask, ValueTuple, function pointers, ref structs, conversions of literals to read-only spans, that eliminate allocations.

DateTime is a value type and doesn't allocate memory. Getting the current time does not allocate memory.

With the recent additions to ref types and Span<>, C# provides a lot of type-safe ways to avoid garbage collections. You can always use pointers if need be.

ayende3y ago

And to put that in context, 2.0 was around 2003, iirc

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pjmlp3y ago

Value types in .NET exist since forever, version 1.0.

Besides the runtime also does C++ since version 1.0, and any language can tap into it.

al_mandi3y ago

The JVM also does escape analysis. Java value types are in the works as well.

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