Hacker News Reader

Comment by gameswithgo | Hacker News Reader

there are a few completely different ways to interpret this, can you explain?

in languages like c, rust or go, where you can put arbitrary data on the stack, it seems to me as if such issues are less common because you dont have to worry about initializing pointers and allocating memory unless you actually want to put something on the heap. Thus if you make everything a reference in your language its no wonder you run into issues like null-pointers more often

With stack allocation you then encounter problems with object lifetime. Rust solves this problem by binding references to scope, and Go solves this by invisibility changing an allocation to the heap (and uses ref-counting? I think?).

I wish C had a feature that would let you allocate something on the stack and then return to the parent stack frame without popping the stack-pointer - that would be handy for self-contained object-constructors.

Regardless of whether it's on the stack or heap the point still stands. If all your objects are randomly allocated then an array is just references to those objects and will start out null. If you're using value types then your array of objects will never be null (empty instead) and you will benefit from CPU caching the data.

Fortunately, objects in modern GC are almost guaranteed to be layed out sequentially in memory of they are allocated sequentially or if they are referenced sequentially and a GC pass has run, because of the way copying GCs work. The much bigger problem is the memory and CPU overhead of storing pointers and following them, though that should be mitigated somewhat by the prefetcher.

Go uses fully-general GC, not reference counting. Obligate reference counting is used in other languages such as Swift, probably with worse throughput than obligate tracing GC.

Plus also doesn’t the stack need to be small to fit into the CPU cache?

There is absolutely no requirement from the hardware that the stack be any particular size

On the Windows desktop, the default stack size is 1MB. In IIS-hosted applications the default stack size is reduced to 250KB due to the popularity of the now-outdated programming trope of "one thread per request (per-connection)". On x86 Linux the default stack size is 2MB - which seems generous.

If you start allocating multi-kilobyte objects in your stack frames, they are not going to fit into L1.

I am not thinking requirement by rather performance wise.

Isn't that just how return values work or did I woosh a joke?

Reply on news.ycombinator.com