They're a great fit in many situations but certainly not all. Why not teach programmers a variety of allocation strategies and how to recognize when each might be a good fit?
In general, everything allocated within an arena has its lifetime tied to that arena. In lots of situations this is a fine or even desirable property (e.g., a single request context in a server application), but can be a tough restriction to work with in situations where you need fine-grained deallocations and possibly want to reuse freed space. The lifetime property can also be a pain to work with in multithreaded scenarios, where you might have multiple threads needing to access data stored in a single arena. Another situation that comes to mind is large long-lived allocations where you might want to have some manual defragmentation in place for performance reasons.
I agree with you 100%. I think arenas are a much lighter burden for the programmer to reason about than lifetimes & access patterns.
But arenas can have one big drawback, and that is if you do a lot of allocations and deallocations, especially in long-running routines, you can essentially leak memory, because arenas are not usually freed until they are going out of scope. This can vary depending on the language and the implementation, though.
My thought to counteract that though is you could offer a ref-counted arena just for this scenario, but I'm not sure what exactly that would look like (automatic once refs hit 0? offer a purge() function like a GC?). I haven't wrapped my head around the ergonomics yet.
> whatever happened to that Parallella "super computer" project?
I had a couple of those. (Well, still do – but not using them for anything now. Mine are the ones with 16 cores, that I got for backing them on Kickstarter when they did their original crowd funding) And I was wondering the same a while ago. This guy that was part of Adapteva, makers of Parallella, is working on some ASIC stuff now it looks like.
And since Adapteva website also says: “Adapteva is now Zero ASIC”, I guess maybe some other people that were originally doing the Parallella thing are now doing ASIC things with that guy too.
