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by switchbak 58 days ago
It's substantially worse on the JVM. One's intuition from C just fails when you have to think about references vs primitives, and the overhead of those (with or without compressed OOPs).

I've met very few folks who understand the overheads involved, and how extreme the benefits can be from avoiding those.
3 comments
Quarrelsome 58 days ago
Conversely I've met many folks who come into managed environments and piss away time trying to wrangle the managed system into how they think it should work, instead of accepting that clever people wrote it and guidelines when followed result in acceptable outcomes.

The sort of insane stuff I've seen on the dotnet repo where people are trying to tear apart the entire type system just because they think they've cracked some secret performance code.

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andai 57 days ago
>on the dotnet repo

You mean the .net compiler/runtime itself? I haven't looked at it, but isn't that the one place you'd expect to see weirdly low-level C# code?

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awesome_dude 58 days ago
My favourite JVM trivia, although I openly admit I don't know if it's still true, is the fact that the size of a boolean is not defined.

If you ask a typical grad the size of a bool they will inevitably say one bit, but, CPUs and RAM, etc don't work like that, typically they expect WORD sized chunks of memory - meaning that the boolean size of one but becomes a WORD sized chunk, assuming that it hasn't been packed

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KnuthIsGod 57 days ago
". While it represents one bit of information, it is typically implemented as 1 byte in arrays, and often 4 bytes (an int) or more as a standalone variable on the stack "
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gf000 57 days ago
In what way is it worse? The range of values they can contain is well-specified.

And you have a frame with an operands stack where you should be able to store at least a 32-bit value. `double` would just fill 2 adjacent slots.

And references are just pointers (possibly not using the whole of the value as an address, but as flags for e.g. the GC) pointing to objects, whose internal structure is implementation detail, but usually having a header and the fields (that can again be reference types).

Pretty standard stuff, heap allocating stuff is pretty common in C as well.

And unlike C, it will run the exact same way on every platform.

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switchbak 56 days ago
I’m saying very few folks understand the cost tradeoffs of using references/objects versus using primitives directly. The difference in memory used for significant amounts of data is huge.

Not to mention indirection costs, but that’s a different issue.

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