# Multithreading: cannot access struct member in another thread in ModernGL/GLFW app

**URL:** <https://discourse.julialang.org/t/multithreading-cannot-access-struct-member-in-another-thread-in-moderngl-glfw-app/113359>\
**Category:** General Usage\
**Tags:** question\
**Created:** [April 22, 2024, 8:42pm UTC](https://discourse.julialang.org/t/multithreading-cannot-access-struct-member-in-another-thread-in-moderngl-glfw-app/113359 "2024-04-22T20:42:39Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![karna48](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/karna48/32/208701_2.png) [@karna48](https://discourse.julialang.org/u/karna48)\
**Post date:** [April 22, 2024, 8:42pm UTC](https://discourse.julialang.org/t/multithreading-cannot-access-struct-member-in-another-thread-in-moderngl-glfw-app/113359/1 "2024-04-22T20:42:40Z")

</div>

I’m trying to play audio in another thread using WAV.jl via @Threads.spawn .  
I do run julia with multiple threads via --threads parameter.  
(referenced data: [SnakeGameCollection/common\_data at main · karna48/SnakeGameCollection · GitHub](https://github.com/karna48/SnakeGameCollection/tree/main/common_data))

It works in a normal program:

```julia
import WAV

struct Sound
    fs
    y
    filename
    function Sound(filename::String)
        y, fs = WAV.wavread(filename)
        new(fs, y, filename)
    end
end

function play(sound::Sound)
    println("start playing ", sound.filename)
    WAV.wavplay(sound.y, sound.fs)
    println("end playing ", sound.filename)
end

function load_play(filename::String)
    y, fs = WAV.wavread(filename)
    WAV.wavplay(y, fs)
end

sound_die = Sound(joinpath("..", "common_data", "die.wav"))
sound_eat = Sound(joinpath("..", "common_data", "eat.wav"))

Threads.@spawn play(sound_die)

for i in 1:10
    println("main thread sleeps!")
    sleep(1)
    play(sound_eat)
end

```

However in my ModernGL/GLFW app it does not work, it freezes when it’s trying to access any member of Sound structure, even the filename::String. But the variant with loading the file inside the thread and then playing it works.  
The minimal example:

```julia
import WAV
using ModernGL, GLAbstraction, GLFW
const GLA = GLAbstraction

struct Sound
    fs
    y
    filename
    function Sound(filename::String)
        y, fs = WAV.wavread(filename)
        new(fs, y, filename)
    end
end

function play(sound::Sound)
    println("start playing ", sound.filename)
    WAV.wavplay(sound.y, sound.fs)
    println("end playing ", sound.filename)
end

function load_play(filename::String)
    y, fs = WAV.wavread(filename)
    WAV.wavplay(y, fs)
end

g_keys = Dict() # GLFW.GetKey did not work for me

window = GLFW.Window(name="sound not working ModernGL/GLFW", resolution=(800, 600))
GLA.set_context!(window)

glClearColor( 0.7, 0.7, 1, 0 )

GLFW.SetKeyCallback(window, (_, key, scancode, action, mods) -> begin
    if action == GLFW.PRESS
        g_keys[key] = true
    else
        g_keys[key] = false
    end
end)

sound_die = Sound(joinpath("..", "common_data", "die.wav"))
sound_eat = Sound(joinpath("..", "common_data", "eat.wav"))

while !GLFW.WindowShouldClose(window)
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    GLFW.SwapBuffers(window)
    GLFW.PollEvents()

    if get(g_keys, GLFW.KEY_ESCAPE, false)
        GLFW.SetWindowShouldClose(window, true)
    end

    if get(g_keys, GLFW.KEY_P, false)
        @Threads.spawn load_play(joinpath("..", "common_data", "die.wav"))
        g_keys[GLFW.KEY_P] = false
    end

    if get(g_keys, GLFW.KEY_K, false)
        @Threads.spawn play(sound_die)
        g_keys[GLFW.KEY_K] = false
    end

    if get(g_keys, GLFW.KEY_O, false)
        @Threads.spawn load_play(joinpath("..", "common_data", "eat.wav"))
        g_keys[GLFW.KEY_O] = false
    end

    if get(g_keys, GLFW.KEY_L, false)
        @Threads.spawn play(sound_eat)
        g_keys[GLFW.KEY_L] = false
    end
   
    if get(g_keys, GLFW.KEY_SPACE, false)
        println("SPACE!")
    end
end
GLFW.DestroyWindow(window)

```

Can GLFW somehow change how threads can access their data?