Expose `vim.*` to uv threads

[lewis6991]

Feature already in Vim?

No

Feature description

Problem

Libuv provides some pretty cool ways to enable multithreading, however they have some pretty big limitations:

1. They only support passing simple types (nil, number, boolean, string, userdata) to/from the main thread.
2. None of the nvim-lua globals (vim.*) are available within the thread.

Solution

Expose all/some of vim.* to uv threads.

At a minimum we should be able to expose: mpack, xdiff and cjson (maybe even treesitter). mpack will resolve 1) since it will allow us to serialize/deseralize more complex types.

Example

local a = ...;
local b = ...;

vim.loop.new_work(
  function(a0, b0)
     return vim.diff(a0, b0)
  end,
  function(r)
    [use diff result]
  end
):queue(a, b)

[bfredl]

we should use luv_set_thread_cb for this. This lets us initialize the shared parts of the vim.* API in a callback.

[hrsh7th]

First, I don't familiar with real parallel programming and clang.
So It's just a question. Is it possible to expose the vim.regex to the thread context?

[bfredl]

It would be a tricky as the vim regex engine likes to do breakcheck. But we need to fix it anyway to be able to use regex inside of luv callbacks.

[hrsh7th]

Thank you for kindful response. I've understand. it's difficult .

[ray-x]

Agree. Some of the APIs (even some of vim.api.*) can not be executed in the thread context.

[lewis6991]

Resolved by #17386