The default queue implementation is mostly FIFO and it is not
exchangeable unless we implement the whole `workqueue.Interface` which
is less desirable as we have to duplicate a lot of code. There was one
attempt done in [kubernetes/kubernetes#109349][1] which tried to
implement a priority queue. That is really useful and [knative/pkg][2]
implemented something called two-lane-queue. While two lane queue is
great, but isn't perfect since a full slow queue can still slow down
items in fast queue.
This change proposes a swappable queue implementation while not adding
extra maintenance effort in kubernetes community. We are happy to
maintain our own queue implementation (similar to two-lane-queue) in
downstream.
[1]: https://github.com/kubernetes/kubernetes/pull/109349
[2]: https://github.com/knative/pkg/blob/main/controller/two_lane_queue.go
Kubernetes-commit: 87b4279e07349b3c68f16f69a349a02bddd12f25
It turned out that there were lots of unnecessary accessor functions being called locking and unlocking the cond which are not needed because Wait() automatically unlocks and locks the cond for us and best practice says we should run it in a for checking for the condition (so this is what I have done).
Kubernetes-commit: 2b12df56b0be93bc2cac7c5a66342c0ffaa72311
Problem:
When calling newQueue metrics can be of type noMetrics when just calling
New. When doing this a new goroutine is created to update the metrics
but in this case there are no metrics so it's just creating goroutines
that don't do anything but consume resources.
Solution:
If the incoming metrics is of type noMetrics, don't start the goroutine
Kubernetes-commit: de021396f81ff438899297a6f464c70113b58475
