Fixes: kubernetes#90581 (the first part)
When `Close()` is invoked on an empty queue, the control loop inside `Pop()` has a small chance of missing the signal and blocks indefinitely due to a race condition. This PR eliminates the race and allows the control loop inside any blocking `Pop()` to successfully exit after Close() is called.
Kubernetes-commit: d8b90955519d10b99415515f8314dd6d35caae8d