[foundry27]

tl;dr for anyone who may be put off by the article length:

OP built an arena allocator in Go using unsafe to speed allocator operations up, especially for cases when you're allocating a bunch of stuff that you know lives and dies together. The main issue they ran into is that Go's GC needs to know the layout of your data (specifically, where pointers are) to work correctly, and if you just allocate raw bytes with unsafe.Pointer, the GC might mistakenly free things pointed to from your arena because it can't see those pointers properly. But to make it work even with pointers (as long as they point to other stuff in the same arena), you keep the whole arena alive if any part of it is still referenced. That means (1) keeping a slice (chunks) pointing to all the big memory blocks the arena got from the system, and (2) using reflect.StructOf to create new types for these blocks that include an extra pointer field at the end (pointing back to the Arena). So if the GC finds any pointer into a chunk, it’ll also find the back-pointer, therefore mark the arena as alive, and therefore keep the chunks slice alive. Then they get into a bunch of really interesting optimizations to remove various internal checks and and write barriers using funky techniques you might not've seen before