---
title: LockOSThread
---

## Introduction

Some libraries—especially graphical frameworks and libraries like Cocoa, OpenGL, and libSDL—use thread-local state and can require functions to be called only from a specific OS thread, typically the 'main' thread. Go provides the `runtime.LockOSThread` function for this, but it's notoriously difficult to use correctly.

## Solutions

Russ Cox presented a good solution for this problem in this [thread](https://groups.google.com/d/msg/golang-nuts/IiWZ2hUuLDA/SNKYYZBelsYJ).

```Go
package sdl

// Arrange that main.main runs on main thread.
func init() {
	runtime.LockOSThread()
}

// Main runs the main SDL service loop.
// The binary's main.main must call sdl.Main() to run this loop.
// Main does not return. If the binary needs to do other work, it
// must do it in separate goroutines.
func Main() {
	for f := range mainfunc {
		f()
	}
}

// queue of work to run in main thread.
var mainfunc = make(chan func())

// do runs f on the main thread.
func do(f func()) {
	done := make(chan bool, 1)
	mainfunc <- func() {
		f()
		done <- true
	}
	<-done
}
```

And then other functions you write in package sdl can be like

```Go
func Beep() {
	do(func() {
		// whatever must run in main thread
	})
}
```