example_win32_directx12 crashes at startup in debug mod

[LeoGautheron]

I'm using the docking branch on commit eae6e96 Nov 19, 2025.

When I compile the example_win32_directx12 in debug mode x64 on my Windows 11 with Visual Studio 22, and then try to run the generated exe, the GUI appears as a white window that seems to try to load for 5-10 secs, and then it closes unexpetedly without showing any error.

If I start the debugger inside Visual Studio for this example, it shows the following in the output
D3D12 WARNING: ID3D12Fence1::SetEventOnCompletion: Fence values can never be less than zero, so waiting for a fence value of zero will always be satisfied [ EXECUTION WARNING #1424: FENCE_ZERO_WAIT]
D3D12: BREAK enabled for the previous message, which was: [ WARNING EXECUTION #1424: FENCE_ZERO_WAIT ]
Exception thrown at 0x00007FFA261380DA (KernelBase.dll) in example_win32_directx12.exe: 0x0000087A (parameters: 0x0000000000000002, 0x000000956ADDBDE8, 0x000000956ADDCB90).

and at the same time it shows that the exception occured at this line of code
HRESULT result = g_pSwapChain->ResizeBuffers(0, (UINT)LOWORD(lParam), (UINT)HIWORD(lParam), desc.Format, desc.Flags);

I found out that if I comment out this line
pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_WARNING, true);
it no longer crashes.

[ocornut]

Hmm, maybe @RT2Code would know?

[RT2Code]

It's not exactly a crash : In the imgui D3D12 example, the debug layer is configured to trigger an exception on warnings, that's why it works if you remove this line : pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_WARNING, true);. This warning was here before #8961 and should have been fixed by it :

Viewports synchronization is handled differently: Before each call to ExecuteCommandLists, the command queue always waits on the last signaled fence value. This means it never allows multiple frames in flight, since it always waits for the previously submitted frame context to finish before starting the next one. It also produces warnings on the first frame because it waits on fence value 0: D3D12 WARNING: ID3D12CommandQueue1::Wait: Fence values can never be less than zero, so waiting for a fence value of zero will always be satisfied [ EXECUTION WARNING #1424: FENCE_ZERO_WAIT]

Can you double check that you are indeed using the latest imgui commit to rule that out?

I can't reproduce this on my end, but the only explanation I can think of for this warning to still appear after #8961 is that resizing is being triggered before the first frame is drawn, which would cause WaitForPendingOperations to run while the fence value is still 0.

Could you try the following fix? In main.cpp, locate the WaitForPendingOperations function and add this at the beginning:

    if (g_fenceLastSignaledValue == 0)
        return;

Then in example_win32_directx12.cpp, add this at the beginning of the ImGui_WaitForPendingOperations function :

    if (bd->FenceLastSignaledValue == 0)
        return;

Let me know if this resolves the issue.

[LeoGautheron]

I just cloned again https://github.com/ocornut/imgui.git to be sure and I switched to docking, so yes I think I'm at the latest.

I added at the start of WaitForPendingOperations this code

    if (g_fenceLastSignaledValue == 0)
    {
        std::cout << "return1";
        return;
    }

and indeed it showed that it returned.
But I still get the same warning in the debugger and the exe fails in the same way as before.

I also added the return if bd->FenceLastSignaledValue is 0 inside imgui_impl_dx12.cpp, but it was not called before the crash.

[RT2Code]

Thanks for trying my suggestion. I’m really puzzled by your issue because, after carefully re-reading the synchronization code, I can’t find any path where SetEventOnCompletion could possibly be called with a fence value of 0, I made sure of it when I made #8961. There's 5 calls sites :

• WaitForPendingOperations/ImGui_WaitForPendingOperations : Here we flush the GPU, the fence value is incremented immediately and unconditionally before SetEventOnCompletion, so the value here cannot be less than 1.
• ImGui_ImplDX12_UpdateTexture : Same as before, this is a GPU flush, the fence value is incremented immediately before we call SetEventOnCompletion so the value cannot be less than 1.
• WaitForNextFrameContext/ImGui_WaitForNextFrameContext : We only call SetEventOnCompletion if fence->GetCompletedValue() < FenceValue, and since fences are always positive values, this condition can only be true if FenceValue is at least 1.

The only theoretical way to end up with a fence value of 0 is if it overflowed after reaching UINT64_MAX. But that would require running the program for an absurd amount of time (around 4.8 billion years at 120 FPS), so we can safely rule that out as well. 😛

Could you try adding assert(fence_value > 0) immediately before each call to SetEventOnCompletion and see if any of them trigger (Don’t forget to remove the checks I asked you to add earlier)? That would confirm the warning and give us a starting point to track down the issue. A copy of your callstack would also be very useful.

[LeoGautheron]

I hope I did it right, I added two asserts, but none of them triggered.
I added assert(g_fenceLastSignaledValue > 0); in "WaitForPendingOperations" before "SetEventOnCompletion"
and assert(frame_context->FenceValue > 0); in "WaitForNextFrameContext" before "SetEventOnCompletion"
I also added a std::cout before each assert.

Only the first one was called only once with "1" for g_fenceLastSignaledValue

The full stack trace is (before modifying the code)

 	KernelBase.dll!00007ffa261380da()	Unknown
 	DXGIDebug.dll!00007ff93af04f4f()	Unknown
 	d3d12SDKLayers.dll!00007ff91eff5518()	Unknown
 	d3d12SDKLayers.dll!00007ff91ef3de66()	Unknown
 	d3d12SDKLayers.dll!00007ff91ef20787()	Unknown
 	d3d12SDKLayers.dll!00007ff91efde6d7()	Unknown
 	dxgi.dll!00007ffa229b69f5()	Unknown
 	dxgi.dll!00007ffa229ad600()	Unknown
 	dxgi.dll!00007ffa229ad2f8()	Unknown
 	dxgi.dll!00007ffa22988dcf()	Unknown
>	example_win32_directx12.exe!WndProc(HWND__ * hWnd, unsigned int msg, unsigned __int64 wParam, __int64 lParam) Line 548	C++
 	[External Code]	
 	example_win32_directx12.exe!main(int __formal, char * * __formal) Line 131	C++
 	[External Code]	

[RT2Code]

Did you also remove the checks I asked you to add in my first reply?

    if (g_fenceLastSignaledValue == 0) // Remove
        return; // Remove

I initially forgot to mention it and later edited my message, so you may have missed it.

Which DirectX SDK version are you using? You can check it in Visual Studio : run the program, open the Modules window, and look at the version of d3d12SDKLayers.dll :

[LeoGautheron]

I just cloned at the latest 1.9.5 version in docking branch, to be sure.
The only modification I did was to include iostream and I added std::cout just before the 2 SetEventOnCompletion in main.cpp and the 3 in imgui_impl_dx12.cpp
and only the one in WaitForPendingOperations is called once with a value g_fenceLastSignaledValue equal to 1 before the crash.

Here are the dll versions I have in Visual Studio

KernelBase.dll	KernelBase.dll	C:\Windows\System32\KernelBase.dll	N/A	No	Symbol loading disabled by Include/Exclude setting.		4	10.0.26100.7171 (WinBuild.160101.0800)	<Unknown>	00007FFCD2040000-00007FFCD2438000	[18764] example_win32_directx12.exe		
d3d12SDKLayers.dll	d3d12SDKLayers.dll	C:\Windows\System32\d3d12SDKLayers.dll	N/A	No	Cannot find or open the PDB file.		37	10.0.26100.7019 (WinBuild.160101.0800)	<Unknown>	00007FFBDFA60000-00007FFBDFEFB000	[15112] example_win32_directx12.exe		
dxgi.dll	dxgi.dll	C:\Windows\System32\dxgi.dll	N/A	No	Symbol loading disabled by Include/Exclude setting.		18	10.0.26100.7019 (WinBuild.160101.0800)	<Unknown>	00007FFCCE0D0000-00007FFCCE209000	[18764] example_win32_directx12.exe		

[RT2Code]

After looking into this further, I found this discussion on the Unreal Engine developer forum: https://forums.unrealengine.com/t/running-a-game-with-d3ddebug-spams-with-fence-zero-wait/2618843/2

I had the same suspicion, that this is a bug in the D3D12 SDK layer. As I explained in my previous post, with the new synchronization logic it’s impossible for SetEventOnCompletion to receive a fence value of 0, so the warning is simply incorrect. I also wondered whether the warning might be a side effect of a deeper synchronization issue, but that doesn’t seem to be the case, since everything works properly when you disable breaking on warnings.

I'd like you to try the following fix: In main.cpp, disable breaking on the D3D12_MESSAGE_ID_FENCE_ZERO_WAIT warning like this:

    // [DEBUG] Setup debug interface to break on any warnings/errors
#ifdef DX12_ENABLE_DEBUG_LAYER
    if (pdx12Debug != nullptr)
    {
        ID3D12InfoQueue* pInfoQueue = nullptr;
        g_pd3dDevice->QueryInterface(IID_PPV_ARGS(&pInfoQueue));
        pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_ERROR, true);
        pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_CORRUPTION, true);
        pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_WARNING, true);
        pInfoQueue->SetBreakOnID(D3D12_MESSAGE_ID_FENCE_ZERO_WAIT, false); // Add this line to disable breaking on this specific warning
        pInfoQueue->Release();
        pdx12Debug->Release();
    }
#endif

This should fix your issue. If it does, I'll submit a new PR with this change.

[LeoGautheron]

I just tested tested your proposed solution to add
pInfoQueue->SetBreakOnID(D3D12_MESSAGE_ID_FENCE_ZERO_WAIT, false);
but it fails in the same way.
I did several tests to see why. First I commented
pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_WARNING, true);
and it works. Then while still commented, I added
pInfoQueue->SetBreakOnID(D3D12_MESSAGE_ID_FENCE_ZERO_WAIT, true);
and indeed it crashed.
So it would seem that when "D3D12_MESSAGE_SEVERITY_WARNING" is present at true, it ignores to set just after "D3D12_MESSAGE_ID_FENCE_ZERO_WAIT" to false.
I even try to put "D3D12_MESSAGE_ID_FENCE_ZERO_WAIT" to false in a line just before D3D12_MESSAGE_SEVERITY_WARNING:true, but it failed in the same way

[RT2Code]

Thanks for testing. I wrongly assumed this would be enough to disable breaking on this warning, but this is clearly not. Try this instead:

    // [DEBUG] Setup debug interface to break on any warnings/errors
#ifdef DX12_ENABLE_DEBUG_LAYER
    if (pdx12Debug != nullptr)
    {
        ID3D12InfoQueue* pInfoQueue = nullptr;
        g_pd3dDevice->QueryInterface(IID_PPV_ARGS(&pInfoQueue));
        pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_ERROR, true);
        pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_CORRUPTION, true);
        pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_WARNING, true);

        D3D12_MESSAGE_ID disabledMessages[] = { D3D12_MESSAGE_ID_FENCE_ZERO_WAIT };

        D3D12_INFO_QUEUE_FILTER filter = {};
        filter.DenyList.NumIDs = 1;
        filter.DenyList.pIDList = disabledMessages;

        pInfoQueue->AddStorageFilterEntries(&filter);

        pInfoQueue->Release();
        pdx12Debug->Release();
    }
#endif

[LeoGautheron]

yes ! it works

[RT2Code]

Awesome. The PR is up : #9093

Thanks for reporting this and for helping to fix the issue.

[ocornut]

Pushed fix f0699ef. I forgot to include the changelog blurb it'll come in a next commit.