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by gf000 16 days ago
What "work" do we do needlessly? It's a pointer bump. With reclamation being no work. Comparatively a malloc call will have to do extra work to defragment.

Also, a stack is not a separate hardware element of the RAM, it's not faster than a sufficiently hot part of the heap - it just so happens that the current stack frame is pretty likely to be in cache.
1 comments
tialaramex 16 days ago
> What "work" do we do needlessly? It's a pointer bump

Any work here was needless. There was no need to do work.

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gf000 16 days ago
On the allocation happy path there is literally less work in case of Java. Like at least try to get what I'm saying and argue with that - I'm not saying that Java is faster or whatever, but that it has chosen different tradeoffs, and "stack vs heap" is an oversimplified model that doesn't help us understand the real performance impacts.

A pointer bump is a pointer bump, vs a malloc call that will try to find place, do some housekeeping, etc. And your Vec will need at least a single allocation, the backing buffer is not on the stack.

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tialaramex 15 days ago
> On the allocation happy path there is literally less work in case of Java

Doing more allocations isn't "less work". No matter how many times you mumble "But it's just a pointer bump" the alternative was no work.

> it has chosen different tradeoffs

Sure, it's easier to implement this, the New Jersey style. But that's not a benefit to anybody else, so if you're not Sun Microsystems (which you aren't, Sun no longer exists) then that's not actually a benefit at all and this was a bad trade.

Which is why people have expended an eyewatering amount of effort on Project Valhalla to some day fix this stuff.

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