The items that haven't finished the put aren't actually "in" the queue yet, so I don't see how non-FIFO order of insertion violates any FIFO guarantees for the contents of the queue; until the items are actually "in", they're not sequenced for the purposes of when they come "out". Mandating such a guarantee effectively means orchestrating a queue with a real maxsize equal to the configured maxsize plus the total number of coroutines competing to put items into it.

The guarantee is still being met here; once an item is put, it will be "get"-ed after anything that finished put-ing before it, and before anything that finished put-ing after it.