Provides an mpsc (multi-producer single-consumer) channel wrapped in an
IntGauge that counts the number of currently
queued items. While there is only one [
channel::Receiver], there can be
channel::Sender]s, which are also cheap to clone.
This channel differs from our other channel implementation, [
in that it is just a single queue (vs. different queues for different keys)
with backpressure (senders will block if the queue is full instead of evicting
another item in the queue) that only implements FIFO (vs. LIFO or KLAST).
libra_channel provides an mpsc channel which has two ends