---
title: thread - Coroutines
summary: A Lua thread is a coroutine, not an operating-system thread. Verify availability and permitted use in the X4 UI environment. Coroutines do not authorize engine calls from another OS thread.
section: reference
kind: guide
status: reference
updated: 2026-10-26
tags: ["API","X4"]
sources: ["https://wiki.egosoft.com/X4%20Foundations%20Wiki/Modding%20Support/","https://www.lua.org/manual/5.1/manual.html","https://luajit.org/ext_ffi_api.html"]
---
## Meaning

A Lua thread is a coroutine, not an operating-system thread. Verify availability and permitted use in the X4 UI environment. Coroutines do not authorize engine calls from another OS thread.

## Example

```lua
local function describe(value)
  return type(value)
end
```

**What happens:** Only describe is declared; this fragment does not create a coroutine.

This fragment does not print or write a log message. The values shown are the expected results of the example.

## Methods and related calls

[API reference](wiki:api-index).