Multi-viewport : crash at exit when backend code is in a DLL

[olivier-gerard]

Version/Branch of Dear ImGui:

Version 1.92.3, Branch: docking

Back-ends:

imgui_impl_vulkan.cpp + imgui_impl_glfw.cpp

Compiler, OS:

Windows 11 + visual studio

Full config/build information:

No response

Details:

I just moved on to the docking branch and experience a crash at app exit.
A specificity of my code is that the backend code is in a DLL : the app creates the context, the DLL imports it.
Then at each frame, basically the DLL call NewFrame(), call callback for the app the create the GUI, then the DLL call Render().
This is not the most efficient scheme but I had to do so due to internal constraints (the DLL contains specific vulkan code and is also used by other apps).
Well, I had no issue with the master branch, and now it crashes with docking.

The issue come frome the fact that ImGui_ImplVulkan_InitMultiViewportSupport and ImGui_ImplVulkan_ShutdownMultiViewportSupport are not symetrical.
The init sets many function pointers (eg platform_io.Renderer_DestroyWindow = ImGui_ImplVulkan_DestroyWindow;), which are not valid once the DLL is terminated.
I suggest that the shutdown function, after calling ImGui::DestroyPlatformWindows(); shall clear the callbacks. So when DestroyPlatformWindows will be called by DestroyContext it will just do nothing.
Or maybe removing the call to DestroyPlatformWindows in Shutdown, as it was already done by the backend ?

Screenshots/Video:

No response

Minimal, Complete and Verifiable Example code:

No response

[ocornut]

I can confirm that there's an issue specifically (and only) with the main viewport, as viewport->PlatformWindowCreated is not cleared in DestroyPlatformWindow(). But you are right that in principle the handlers should be cleared.

I'll see what I can do. In the meanwhile you can clear the Renderer_DestroyWindow and Platform_DestroyWindow handler in ImGuiPlatformIO after calling ImGui_ImplXXXX_Shutdown(), they should be the only one ever called?

Or maybe removing the call to DestroyPlatformWindows in Shutdown, as it was already done by the backend ?

That's not possible as it would assume that the backend was shutdown.

[ocornut]

Not clearing the flag is caused 1ca6ff9 (#2769)

[olivier-gerard]

Thanks for your quick feedback.
I confirm Renderer_DestroyWindow and Platform_DestroyWindow are the only handler called on exit.
I have no more crash with this small fix.

Or maybe removing the call to DestroyPlatformWindows in Shutdown, as it was already done by the backend ?

That's not possible as it would assume that the backend was shutdown.

Shutdown() is beginning with an assert checking that the plateform and rendered have been shutdown, this is not enough ?

[ocornut]

Shutdown() is beginning with an assert checking that the plateform and rendered have been shutdown, this is not enough ?

Oh you are right.... this is relatively new.
I added clearing every handler (with a helper) but I realize this might make better sense now...

[ocornut]

Pushed 16b2d20, aa9476a, 1ad9de5, this should be all fixed now.
Thanks for reporting!