Module tower_balance::pool

This module defines a load-balanced pool of services that adds new services when load is high.

The pool uses poll_ready as a signal indicating whether additional services should be spawned to handle the current level of load. Specifically, every time poll_ready on the inner service returns Ready, [Pool] consider that a 0, and every time it returns Pending, [Pool] considers it a 1. [Pool] then maintains an exponential moving average over those samples, which gives an estimate of how often the underlying service has been ready when it was needed "recently" (see [Builder::urgency]). If the service is loaded (see [Builder::loaded_above]), a new service is created and added to the underlying [Balance]. If the service is underutilized (see [Builder::underutilized_below]) and there are two or more services, then the latest added service is removed. In either case, the load estimate is reset to its initial value (see [Builder::initial] to prevent services from being rapidly added or removed.

Structs

Builder	A builder that lets you configure how a [Pool] determines whether the underlying service is loaded or not. See the module-level documentation and the builder's methods for details.
Pool	A dynamically sized, load-balanced pool of Service instances.
PoolDiscoverer	A wrapper around MakeService that discovers a new service when load is high, and removes a service when load is low. See [Pool].