[hmry]

Does the stackfull async implementation use the stack-switching proposal? I was under the impression that it's not implemented in most runtimes (very difficult to retrofit into existing implementations), and only available on x86_64 Linux in wasmtime.

[phickey]

No, the stack switching proposal is not used. Stack switching is a set of core Wasm opcodes that permit a guest to change its own stack. Instead of using opcodes inside the Wasm, the stackful async mode of the component model’s ABI calls out into the component model implementation where it can manipulate the stacks with special host powers - JSPI is sufficient on web engines to express this, and wasmtime manages guest stacks in memory.

When stack switching becomes available in all engines, it will be possible to implement this part of the component model in pure Wasm without host magic, e.g. web engines will be able to avoid the call out to JS to use JSPI.

[hmry]

Thank you, that's great to hear. I was worried it would be a long time before most runtimes could use WASIp3 if it required stack-switching.