It looks like the current wasi libc implements sbrk using the clang builtin to grow, and there isn't a wasi API for growth. I think this may be a problem for a JS embedding (that is, running a wasi program with JS implementing the wasi APIs etc.), as any JS views on the buffer used in the wasm Memory will become invalid - they don't resize automatically, and must be manually recreated. In particular I think the current Web polyfill for wasi probably doesn't fully work with memory growth.

There is no event callback for when a Memory grows, but even if there were, it wouldn't be enough, just like with pthreads - the event would happen on a later JS event loop iteration, and not when we need it.

One possible solution here would be to add an API to wasi that either does the growth (__wasi_grow_memory?), or that notifies the runtime about the growth (__wasi_notify_memory_growth?).