Numba is also really nice, and for just compiling against arrays I like it better than Cython. Neither help if you need data structures or abstractions, though.
Though as I said before, sometimes no amount of c++/c escape hatches can improve performance since you have to use python objects at some point or another and that will be the bottleneck. But by then, you won't needing some of the stuff Julia offers like the REPL and notebooks etc.
I haven't used Julia a lot but to me it's in a weird spot where it would be ideal to start projects with in theory since you won't need to outgrow the language you are starting with, since it's fast enough and has a pretty good/maintainable/sane design. But then you are sacrificing so much and will need much more time to get started that you might not ever get to that point anyways.
Just as an example, debugging obscure problems or deploying pytorch models that are more custom in prod is already pretty daunting at times, and it's the "best" and most popular ML framework in the world. I can't imagine how much more time consuming it would be when using a much smaller/less used library/framework.
So yeah all of that to say that being way faster isn't how Julia will win. Maybe a push from an influent player/big tech might give it the momentum it needs.
There are also some nice demonstrations showing Julia compiled to web assembly. https://tshort.github.io/WebAssemblyCompiler.jl/stable/examp...
There are AOT compilers for JS.
Each thread has its own lua_State. However, we provide a serialization scheme which allows automatic sharing for several Torch objects (storages, tensors and tds types). Sharing of vanilla lua objects is not possible, but instances of classes that support serialization (eg. classic objects with using require 'classic.torch' or those created with torch.class) can be shared, but remember that only the memory in tensor storages and tds objects will be shared by the instances, other fields will be copies. Also if synchronization is required that must be implemented by the user (ie. with mutex).
There is simply too many rough edges and usability problems as it is now, and at the current pace it will take maybe 10 or 15 years to address them.
On the other hand, the major use case for Julia is to have a fast, dynamic language. And it seems to me the time horizon for Python to become fast, or Rust or C++ to become dynamic is indefinite, so Julia is still the best bet in that space.