Can emscripten_fiber_t only be accessed within one thread?

Can `emscripten_fiber_t` only be accessed within one thread? I failed to migrate a coroutine library (many to many model) to the webassembly platform using the emscripten fiber API.

In this coroutine library, each kernel thread (`std:: thread`) has the opportunity to switch to a user thread (based on `emscripten_fiber_t`) through the `emscripten_fiber_ swap` function.