Stream: wasmtime

Topic: ✔ copying Stored state to memory

Guillaume Quintard (Sep 04 2023 at 19:37):

Hi, I've been toying with wasmtime for a few days and have run into something that has me puzzled.
For context, my host has a rust object (couple of fields and a map) and it starts a wasm guest to get some decision, and the logic I went for is:

• host creates a Store with the object
• host links, instantiates and run an exported function
• guest uses an imported function to asks the hosts the size of the serialized rust object
• guest allocates a buffer to receive the serialized object
• guest uses a second imported function so the host copies the object into the aforementioned buffer
  And of course, I run into an issue with borrowing the caller twice, because I need the stored object to read from and the memory to write to.
  The docs seem to acknowledge that:

  Note that all of these consider the entire store context as borrowed for the duration of the call or the duration of the returned slice. This largely means that while the function is running you’ll be unable to borrow anything else from the store. This includes getting access to the T on Store<T>, but it also means that you can’t recursively call into WebAssembly for instance.

But then, am I doing something wrong here? I can of course force my way in with pointers, but that seems very dirty for a fairly simple use-case

Alex Crichton (Sep 04 2023 at 19:54):

I think you might want data_and_store_mut perhaps?

Guillaume Quintard (Sep 05 2023 at 15:02):

ahem, yes, that's it. I should have RTFM'd better. Thank you @Alex Crichton !

Notification Bot (Sep 05 2023 at 15:02):

Guillaume Quintard has marked this topic as resolved.

Last updated: Dec 23 2024 at 13:07 UTC