attempt to modify variable captured in a closure causes segmentation fault #13

julia> mutable struct Simple
           a::Float64
       end

julia> function mwe()
           width = 600
           height = 600
           window = mfb_open_ex("Luxor -> MiniFB", width, height, MiniFB.WF_RESIZABLE)
           t = Simple(1.0)

           function onkeypress(window::Ptr{Cvoid}, key::mfb_key, mod::mfb_key_mod, ispressed::Bool)
               t.a += 1 #this causes the segfault. If t is a global variable no segfault
               return nothing
           end

           mfb_set_target_fps(60)
           mfb_set_keyboard_callback(window, onkeypress)

         
           while mfb_wait_sync(window) # The Luxor `@imagematrix` macro creates a 2D matrix of Color objects in ARGB32 format, which is exactly what MiniFB requires
               buffer = Luxor.@imagematrix begin
                   Luxor.background("grey40")
               end 600 600 
               # The image matrix created by Luxor is, in standard Julia convention, column first. The buffer
               # expected by MiniFB is row first. The call to `permutedims` makes that change.
               state = mfb_update(window, permutedims(buffer, (2, 1)))
               # Exit when the user closes the window.
               if state != MiniFB.STATE_OK
                   break
               end
           end

           mfb_close(window)
       end
mwe (generic function with 1 method)

julia> mwe()

Window created using X11 API

signal (11): Segmentation fault
in expression starting at REPL[5]:1
unknown function (ip: 0x7f7e8800cfc3)
Allocations: 11027408 (Pool: 11024513; Big: 2895); GC: 24
Segmentation fault (core dumped)