Struct tower::balance::pool::Builder

pub struct Builder { /* fields omitted */ }

This is supported on crate feature balance only.

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.

Implementations

impl Builder

pub fn new() -> Self

Create a new builder with default values for all load settings.

If you just want to use the defaults, you can just use Pool::new.

pub fn underutilized_below(&mut self, low: f64) -> &mut Self

When the estimated load (see the module-level docs) drops below this threshold, and there are at least two services active, a service is removed.

The default value is 0.01. That is, when one in every 100 poll_ready calls return Pending, then the underlying service is considered underutilized.

pub fn loaded_above(&mut self, high: f64) -> &mut Self

When the estimated load (see the module-level docs) exceeds this threshold, and no service is currently in the process of being added, a new service is scheduled to be added to the underlying Balance.

The default value is 0.5. That is, when every other call to poll_ready returns Pending, then the underlying service is considered highly loaded.

pub fn initial(&mut self, init: f64) -> &mut Self

The initial estimated load average.

This is also the value that the estimated load will be reset to whenever a service is added or removed.

The default value is 0.1.

pub fn urgency(&mut self, alpha: f64) -> &mut Self

How aggressively the estimated load average is updated.

This is the α parameter of the formula for the exponential moving average, and dictates how quickly new samples of the current load affect the estimated load. If the value is closer to 1, newer samples affect the load average a lot (when α is 1, the load average is immediately set to the current load). If the value is closer to 0, newer samples affect the load average very little at a time.

The given value is clamped to [0,1].

The default value is 0.05, meaning, in very approximate terms, that each new load sample affects the estimated load by 5%.

pub fn max_services(&mut self, limit: Option<usize>) -> &mut Self

The maximum number of backing Service instances to maintain.

When the limit is reached, the load estimate is clamped to the high load threshhold, and no new service is spawned.

No maximum limit is imposed by default.

pub fn build<MS, Target, Request>(
    &self,
    make_service: MS,
    target: Target
) -> Pool<MS, Target, Request> where
    MS: MakeService<Target, Request>,
    MS::Service: Load,
    <MS::Service as Load>::Metric: Debug,
    MS::MakeError: Into<BoxError>,
    MS::Error: Into<BoxError>,
    Target: Clone, 

See Pool::new.

Trait Implementations

impl Clone for Builder

pub fn clone(&self) -> Builder

Returns a copy of the value.

pub fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Builder

impl Debug for Builder

pub fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Builder

pub fn default() -> Self

Returns the "default value" for a type.