For reading back data to the host, a barrier is required

[johannesugb]

... and avk::read does not perform such a barrier. Not sure yet, if this issue is a bug or an enhancement, though -- i.e., if it is the responsibility of avk::read to perform the barrier or if it is the user's. But this should be investigated.

Anyways, Vulkan synchronization examples have the following example:

---

CPU read back of data written by a compute shader
This example shows the steps required to get data written to a buffer by a compute shader, back to the CPU.

vkCmdDispatch(...);

VkMemoryBarrier2KHR memoryBarrier = {
  ...
  .srcStageMask = VK_PIPELINE_STAGE_2_COMPUTE_SHADER_BIT_KHR,
  .srcAccessMask = VK_ACCESS_2_SHADER_WRITE_BIT_KHR,
  .dstStageMask = VK_PIPELINE_STAGE_2_HOST_BIT_KHR,
  .dstAccessMask = VK_ACCESS_2_HOST_READ_BIT_KHR};

VkDependencyInfoKHR dependencyInfo = {
    ...
    1,              // memoryBarrierCount
    &memoryBarrier, // pMemoryBarriers
    ...
}

vkCmdPipelineBarrier2KHR(commandBuffer, &dependencyInfo);

vkEndCommandBuffer(...);

vkQueueSubmit2KHR(..., fence); // Submit the command buffer with a fence