The default stack size in most OSes is tiny, and when programming in a low-level language (including Rust) it's important to keep large allocations off of the stack. That's why Rust has Box/Vec and the various APIs in `alloc`, and why the cross-thread primitives take ownership of their values.
You can "transfer" a 1 GiB `Vec` between threads without having to actually copy it, which is not true of stack-allocated values.
The relative scarcity/cost of the stack vs heap only gets more extreme as the machines get bigger. My desktop has 128 GiB of RAM, and `ulimit -s` reports a default thread size of 8 MiB. A typical rack-mounted server is going to have 1 TiB or more of RAM, and almost certainly the same stack size.
Could I make the stack size bigger on my machine? Sure, yes, but what would that get me when the entire world writes software with the assumption that any allocation over a few dozen MiB needs to be on the heap?
You can "transfer" a 1 GiB `Vec` between threads without having to actually copy it, which is not true of stack-allocated values.
The relative scarcity/cost of the stack vs heap only gets more extreme as the machines get bigger. My desktop has 128 GiB of RAM, and `ulimit -s` reports a default thread size of 8 MiB. A typical rack-mounted server is going to have 1 TiB or more of RAM, and almost certainly the same stack size.
Could I make the stack size bigger on my machine? Sure, yes, but what would that get me when the entire world writes software with the assumption that any allocation over a few dozen MiB needs to be on the heap?