A fence is a GPU/CPU synchronization primitive. It's used to lets the CPU know when submitted GPU work has completed.

There is two uses of vireo::Fence :

Synchronize the frame rendering and presenting
Wait for the execution of a work submission

Frame rendering and presenting synchronization

Synchronizing the frame rendering is mandatory if you want multiple frames in flight. You need one vireo::Fence per frame then use them in the rendering loop :

// Get the current frame data
const auto& frame = framesData[swapChain->getCurrentFrameIndex()];
 
// Acquire the next frame buffer or stop rendering on error.
if (!swapChain->acquire(frame.inFlightFence)) { return; }
 
...
// Record commands
...
 
// Submit the frame command list then ask the submission queue to signal the end of the rendering to the swap chain
graphicQueue->submit(frame.inFlightFence, swapChain, {frame.commandList});
 
// Present the swap chain. Presentation will be done when the submission queue will signal the end of the rendering.
// It's a GPU/GPU synchronization mechanism, the CPU will not be blocked, only the swap chain presentation.
swapChain->present();
 
// Get the next frame index for the next frame
swapChain->nextFrameIndex();

Work completion synchronization

Waiting for a command submission to end involve creating a vireo::Fence with vireo::Vireo::createFence, use it with vireo::SubmitQueue::submit then vireo::Fence::wait (blocking the CPU code).

At initialization, create the fence in signaled state to be able use vireo::Fence::reset the first time without using a condition :

auto fence = vireo->createFence(true);

Use the fence :

// Reset the fence state
fence->reset()
 
// Submit work
graphicQueue->submit(fence, {commandList});
 
// Wait for the GPU to execute the commands
fence->wait()