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v1.0.0 Public

Weighted Round Robin

This module provides a round-robin algorithm for rotating elements according to differing weights, instead of evenly. It was inspired by the npm package weighted-round-robin, and uses the same logic for its algorithm.


The module tracks elements that you wish to distribute in a weighted round-robin rotation. They're added to the rotation as a struct that, at minimum, contains an id key with a unique identifier (though you'll probably also want to include a weight). If you like, the struct can contain other keys - a name for example.

It stores these elements, either in memory or in a cache, and returns the element struct when you call the module's get() method. These elements will be rotated and returned, according to their weight. Here's an example:

rr = new;

    "id": "heavy",
    "weight": 6

    "id": "light",
    "weight": 3

    "id": "feather",
    "weight": 1

// you can add as many as needed

for ( i = 0; i < 10; i++ ) {
  writeOutput( rr.get().id & '<br>' );
// heavy, light, heavy, heavy, light, heavy, feather, heavy, heavy, light

Using Memory or a Cache

By default this component stores the round-robin rotation in memory; it is init without any arguments and you should store it as a singleton (or in the application scope).

However, when you're deploying a distributed application (like Docker Swarm), or if you'd like more robust data persistence, you can configure the module to store/track the rotating elements in a remote cache (like Redis). Note that remote caching engines are only available in Lucee or Adobe ColdFusion 2018.

To use this approach, init the component with a cache identifier you'd like the component to use for storing/retrieving the data and the name of the cache region it should use (this defaults to object). For example:

rr = new 
  cacheId = '_roundrobinElements',
  cacheRegion = 'cache_region_name'

When using this approach, you don't necessarily need to store the RoundRobin component in a persistant scope, since the data is tracked/stored separately.

Reference Manual

init( string cacheId = '', string cacheRegion = 'object' )

When the component is init with a cacheId and cacheRegion, the data will be stored in the specified cache, using the provided cacheId, instead of in the component memory, which is the default.

add( required struct element, boolean overwrite = true )

Adds an element to the round-robin rotation. Returns the element's key.

The element is a struct, with at minimum an id key, but if you're using this module, you'll likely also want a weight key. The default weight is 1, which will be used if no weight is provided.

By default, if you try to add() an element that already exists, it is ignored. If you want to overwrite the existing element, set the overwrite parameter to true.


Returns the next element in the round-robin rotation. The full struct is returned.

remove( required any key )

Removes an element from the round-robin rotation.


Restores all elements in the round-robin rotation to their original weight, effectively restarting the rotation.


Removes all elements from the rotation, leaving it empty.


Returns the round-robin rotation struct so you can see elements and their weights. Helpful for debugging.


Returns the number of elements being tracked in the rotation.


Returns true or false, depending on if the component is using a cache for storing the data or not.


For questions that aren't about bugs, feel free to hit me up on the CFML Slack Channel; I'm @mjclemente. You'll likely get a much faster response than creating an issue here.


👍 🎉 First off, thanks for taking the time to contribute! 🎉 👍

Before putting the work into creating a PR, I'd appreciate it if you opened an issue. That way we can discuss the best way to implement changes/features, before work is done.

Changes should be submitted as Pull Requests on the develop branch.

Dependencies (0)

Dev Dependencies (1)


$ box install weightedroundrobin

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  • Jul 13 2020 05:47 PM
  • Jul 13 2020 05:47 PM
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