anlawande/promise-pc

A Promise implementation of the producer consumer problem

promise-pc

New functionality! - Tree notify, see below

A Promise implementation of the producer-consumer problem.

Basically a queue in which you can keep adding promises. Consumer(s) consume promises and notify the producer. Uses the then/promise implementation.

Number of consumers is dynamic. (Coming soon. Currently changing the maxParallel after initialization does not do anything)

Usage

• Require the module and initialize a PCQueue

var PCQueue = require("promise-pc").PCQueue;
var pcqueue = new PCQueue(opts);

See below for available options

• When an item is ready to be consumed, a producer pushes it onto the queue using the produce method.

var promise = pcqueue.produce(function() {
  //This is a consumer function
  
  //Must return a promise object
});

promise.then(function(result){  //Use 'done' instead of 'then' if you wish to propagate errors
//Producer is notified after a consumer consumes an item
//Results of consumption are available here
});

Note that the consumer function is not immediately invoked. Only when a consumer is free (as indicated by the maxParallel option).

Tree Notify

Many a times processing of a tree or tree like structure requires async processing. On a node per node basis there is no difference in production and consumption. But at a tree level, it may be needed to be notified when tree processing is complete. The treeNotify event can be used to be notified once all the nodes of a tree are finished being processed by the consumer.

This is done by

1. Declaring tree option as true
2. Using treeNotify event to be notified of tree processing completion
3. During producer/consumer processing, using children method to declare number of children current node has.

See tree test in tests.js

pcqueue.treeNotify(function() {/*Do something*/});

//Inside producer/consumer processing
pcqueue.children(node.children.length);

Options

• maxParallel : Maximum number of consumers. If not specified, assumes inifite number of consumers
• tree : Enables tree mode wherein treeNotify event is available