Function wait_render_fence 

pub(crate) fn wait_render_fence(sync: &SyncPoint, display_id: u32) -> bool

Wait, bounded, for a render’s fence to signal before the tick reuses or releases the buffers it sampled.

A client buffer a render read can be released and destroyed by the client’s next commit (a nested session swaps its swapchain across a mode change); without implicit dmabuf fencing the driver then frees it under an unfinished read and faults the channel, after which no fence of the context signals. The bound turns that into a logged, dropped frame rather than a compositor thread parked forever. The wait is one eglClientWaitSync to the deadline, flushing whatever commands still queue ahead of the fence; a fence-less sync point is reached at once.