title: Why does vkAcquireNextImageKHR() never block my thread?
body: <p>I am using <a href="https://vulkan-tutorial.com/" rel="noreferrer">Vulkan graphics</a> API (via <a href="https://github.com/bkaradzic/bgfx" rel="noreferrer">BGFX</a>) to render. And I have been measuring how much (wall-clock) time my calls take.</p>
  
  <p>What I do not understand is that <a href="https://www.khronos.org/registry/vulkan/specs/1.2-extensions/man/html/vkAcquireNextImageKHR.html" rel="noreferrer">vkAcquireNextImageKHR</a>() is always fast, and never blocks. Even though I disable the time-out and use a semaphore to wait for presentation.</p>
  
  <p>The presentation is locked to a 60Hz display rate, and I see my main-loop indeed run at 16.6 or 33.3 ms.</p>
  
  <p>Shouldn't I see the wait-time for this display rate show up in the length of the <code>vkAcquireNextImageKHR()</code> call?</p>
  
  <p>The profiler measures this call as 0.2ms or so, and never a substantial part of a frame.</p>
  
  <pre><code>VkResult result = vkAcquireNextImageKHR(
      m_device
    , m_swapchain
    , UINT64_MAX
    , renderWait
    , VK_NULL_HANDLE
    , &amp;m_backBufferColorIdx
  );
  </code></pre>
  
  <p>Target hardware is a handheld console.</p>