currently this is not necessary because context (WASINNContext) is
local to instance. (wasm_module_instance_t)
i plan to make a context shared among instances in a cluster when
fixing https://github.com/bytecodealliance/wasm-micro-runtime/issues/4313.
this is a preparation for that direction.
an obvious alternative is to tweak the module instance context APIs
to allow declaring some kind of contexts instance-local. but i feel,
in this particular case, it's more natural to make "wasi-nn handles"
shared among threads within a "process".
note that, spec-wise, how wasi-nn behaves wrt threads is not defined
at all because wasi officially doesn't have threads yet. i suppose, at
this point, that how wasi-nn interacts with wasi-threads is something
we need to define by ourselves, especially when we are using an outdated
wasi-nn version.
with this change, if a thread attempts to access a context while
another thread is using it, we simply make the operation fail with
the "busy" error. this is intended for the mimimum serialization to
avoid problems like crashes/leaks/etc. this is not intended to allow
parallelism or such.
no functional changes are intended at this point yet.
cf.
https://github.com/bytecodealliance/wasm-micro-runtime/issues/4313https://github.com/bytecodealliance/wasm-micro-runtime/issues/2430
ea408ab6c0