engine/3rdparty/sol2-3.3.0/documentation/source/api/thread.rst
a separate state that can contain and run functions
.. code-block:: cpp
class thread : public reference { /* ... */ };
sol::thread is a separate runnable part of the Lua VM that can be used to execute work separately from the main thread, such as with :doc:coroutines<coroutine>. To take a table or a coroutine and run it specifically on the sol::thread you either pulled out of lua or created, just get that function through the :ref:state of the thread<thread_state>
.. note::
A CPU thread is not always equivalent to a new thread in Lua: ``std::this_thread::get_id()`` can be the same for 2 callbacks that have 2 distinct Lua threads. In order to know which thread a callback was called in, hook into :doc:`sol::this_state<this_state>` from your Lua callback and then construct a ``sol::thread``, passing in the ``sol::this_state`` for both the first and last arguments. Then examine the results of the status and ``is_...`` calls below.
.. code-block:: cpp :caption: function: main_thread
main_thread(lua_State* current, lua_State* backup_if_bad_platform = nullptr);
The function sol::main_thread( ... ) retrieves the main thread of the application on Lua 5.2 and above only. It is designed for code that needs to be multithreading-aware (e.g., uses multiple :doc:threads<thread> and :doc:coroutines<coroutine>).
.. warning::
This code function will be present in Lua 5.1/LuaJIT, but only have proper behavior when given a single argument on Lua 5.2 and beyond. Lua 5.1 does not support retrieving the main thread from its registry, and therefore it is entirely suggested if you are writing cross-platform Lua code that you must store the main thread of your application in some global storage accessible somewhere. Then, pass this item into the ``sol::main_thread( possibly_thread_state, my_actual_main_state )`` and it will select that ``my_actual_main_state`` every time. If you are not going to use Lua 5.1 / LuaJIT, you can ignore the last parameter.
.. code-block:: cpp :caption: constructor: thread
thread(stack_reference r);
thread(lua_State* L, int index = -1);
thread(lua_State* L, lua_State* actual_thread);
Takes a thread from the Lua stack at the specified index and allows a person to use all of the abstractions therein. It can also take an actual thread state to make a thread from that as well.
.. code-block:: cpp :caption: function: view into thread_state()'s state
state_view state() const;
This retrieves the current state of the thread, producing a :doc:state_view<state> that can be manipulated like any other. :doc:Coroutines<coroutine> pulled from Lua using the thread's state will be run on that thread specifically.
.. _thread_state:
.. code-block:: cpp :caption: function: retrieve thread state object
lua_State* thread_state () const;
This function retrieves the lua_State* that represents the thread.
.. code-block:: cpp :caption: current thread status
thread_status status () const;
Retrieves the :doc:thread status<types> that describes the current state of the thread.
.. code-block:: cpp :caption: main thread status
bool is_main_thread () const;
Checks to see if the thread is the main Lua thread.
.. code-block:: cpp :caption: function: thread creation :name: thread-create
thread create();
static thread create (lua_State* L);
Creates a new thread from the given a lua_State*.