Hopper—an MPSC specialization

As mentioned at the tail end of the last chapter, you'd need a fairly specialized use-case to consider not using stdlib's MPSC. In the rest of this chapter, we'll discuss such a use-case and the implementation of a library meant to fill it.

The problem

Recall back to the last chapter, where the role-threads in telem communicated with one another over MPSC channels. Recall also that telem was a quick version of the cernan (https://crates.io/crates/cernan) project, which fulfills basically the same role but over many more ingress protocols, egress protocols, and with the sharp edges worn down. One of the key design goals of cernan is that if it receives your data, it will deliver it downstream at least once. This implies that, for supporting ingress protocols, cernan must know, along the full length of the configured routing topology, that there is sufficient space to accept a new event, whether it's a piece of telemetry, a raw byte buffer, or a log line. Now, that...