Validation error in hello_triangle: semaphore must not be currently signaled.

[MarkCallow]

This is on Ubuntu 24.04 with "mesa-vulkan-drivers/noble-updates,noble-updates,noble-security,now 25.2.8-0ubuntu0.24.04.2".

This is a new validation check in Vulkan SDK 1.4.357. It happens in my own app so, looking for a solution, I tried hello_triangle but it suffers too. To reproduce, simply resize the window.

Here is the error.

Validation Error: [ VUID-vkAcquireNextImageKHR-semaphore-01286 ] | MessageID = 0xe9e4b2a9
vkAcquireNextImageKHR(): Semaphore must not be currently signaled.
The Vulkan spec states: If semaphore is not VK_NULL_HANDLE, it must be unsignaled (https://vulkan.lunarg.com/doc/view/1.4.357.1/linux/antora/spec/latest/chapters/VK_KHR_surface/wsi.html#VUID-vkAcquireNextImageKHR-semaphore-01286)
Objects: 1
    [0] VkSemaphore 0x1d100000001d1

I believe this is because the driver is signalling the semaphore when it returns VK_SUBOPTIMAL_KHR. In this case acquire_next_image pushes the semaphore onto recycled_semaphores and returns to update
which calls resize() then acquire_next_image() again which proceeds to pull the signaled semaphore off recycled_semaphores and reuses it. The same recycling happens if the second acquire_next_image fails.

acquire_next_image
	VkResult res = vkAcquireNextImageKHR(context.device, context.swapchain, UINT64_MAX, acquire_semaphore, VK_NULL_HANDLE, image);

	if (res != VK_SUCCESS)
	{
		context.recycled_semaphores.push_back(acquire_semaphore);
		return res;
	}
        ...
}

void HelloTriangle::update(float delta_time)
{
        ...
	auto res = acquire_next_image(&index);

	// Handle outdated error in acquire.
	if (res == VK_SUBOPTIMAL_KHR || res == VK_ERROR_OUT_OF_DATE_KHR)
	{
		resize(context.swapchain_dimensions.width, context.swapchain_dimensions.height);
		res = acquire_next_image(&index);
	}

	if (res != VK_SUCCESS)
	{
		vkQueueWaitIdle(context.queue);
		return;
	}
        ...
}

[MarkCallow]

The semaphore is indeed signaled when the result is VK_SUBOPTIMAL_KHR. Not surprising as the spec. describes this as a successful result. This sample is (and how many others are?) showing invalid usage.

[MarkCallow]

FWIW, the visual appearance of resizing appears smoother on my slow Ubuntu laptop when a VK_SUBOPTIMAL_PRESENT is allowed to proceed rather than recreating the swapchain. Of course, it is very subjective.