conduit-throttle

About

This is conduit-throttle, a compact Haskell package providing configurable throttling support for Conduit. It is built on top of the packages throttle-io-stream and unliftio.

The API (Data.Conduit.Throttle) is designed for being imported qualified, which is why the exported functions and values are not prefixed by the package name or something similar.

The core function exported by this package is the following:

throttleProducer :: (MonadUnliftIO m, MonadResource m)
                 => Conf a
                 -> Producer m a
                 -> Producer m a

That is, given a configuration and a Conduit Producer, create and return a new Conduit Producer, which yields the same stream of values like the provided one but throttled according to the provided throttling configuration.

A throttling configuration is created using newConf and then configured using the functions setMeasure, setMaxThroughput, setBufferSize and others.

Primarily, the throughput is defined by the provided measure function and the configured maximum throughput. A measure function is a function which defines how “big” a Conduit element a is. In other words, it is a function of type a -> Double. For instance, it could simply calculate the length of some deserialized value in bytes or it could simply be the constant function const 1 in case it is desired to throttle the number of elements a Conduit producer produces. The maximum throughput together with the measure function then defines the maximum throughput to produce (of course it can be less, if the original producer provides data with a smaller throughput). The throughput is considered with respect to a base time interval, which can be changed using setInterval, by default it is 1000 (ms).

The underlying package throttle-io-stream uses exponentially weighted moving averages for smoothing the actual throughput changes.

Example

import qualified Data.Conduit.Throttle as ConduitThrottle

simpleProducerThrottling :: IO ()
simpleProducerThrottling = do
  let conf = ConduitThrottle.newConf
             & ConduitThrottle.setInterval 1000
             & ConduitThrottle.setMaxThroughput 1
  runResourceT . runConduit $
    ConduitThrottle.throttleProducer conf (sourceList [1..5]) .| printC