Hacker News Reader

Comment by Arnavion | Hacker News Reader

>specifically since modules don't share their wasm Memory. That means data will be constantly copied between them.

It is possible today to have modules import memory from the host, which means the host can provide the same imported memory to multiple modules. Then modules can pass pointers to each other without needing any memcpys.

It does require the modules to not tread on each other though, such as by requiring them to have distinct static offsets (poor man's linking), or by requiring them to be PIC / compiled with relocation info so that they can be relinked by the host loader.

It doesn't seem to me from reading TFA that this is going away, merely that there are planning to add alternatives to make it more fine-grained.

View on HN

It is possible to share memory in wasm today, yes (we use that to optimize wasm/JS interaction, and wasm/wasm dynamic linking) - and that won't go away, it's a core feature of wasm, you're right. But the specific approach in this article disallows that.

The article does mention a possible future extension of multiple wasm modules in a single nanoprocess (the section with "allowing native-style dynamic linking"), and JoshTriplett mentions in another comment some future ideas of sharing parts of memory but not all. Those things will compromise the strict initial requirement of no shared memory, and improve performance.

Those are the interesting questions for me - is not sharing memory too much overhead, and if it is, is there a way to relax that which preserves enough security with enough performance.

To the question of "how would dynamic linking work in the future", as already stated in the article, a nanoprocess doesn't need to correspond 1:1 to a wasm module/instance. Rather, N wasm instances can share a single wasm memory to collectively represent a single nanoprocess. From an external point of view, whether a nanoprocess is implemented as 1 or N instances wouldn't be visible -- it's an impl detail -- and the memory is (still) encapsulated by the nanoprocess. Thus, there is a two-level hierarchy of: a graph of shared-nothing-linked nanoprocesses each containing a graph of shared-everything wasm instances.

There's still a lot more details to figure out, of course, but that's true for wasm dynamic (shared-everything) linking in general.

Reply on news.ycombinator.com