Push and pull: futures and tasks
This description is hopefully not surprising, given the previous few chapters. However, it's important to realize that this setup is drastically different from futures (aka promises) in other languages:
-
Rust futures follow a pull model, where, once a future is blocked by an event, it must be retried through a call to
get(i.e., by repeatedly trying to "pull" a value out). -
Other futures libraries follow a push model, where the completion of one event automatically triggers a cascade of follow-up work, pushing the computation forward. That follow-up work is usually given by registering callbacks with a future.