concurrent-queue

concurrent-queue

Fifo queue with concurrency control

example

var cq = require('concurrent-queue')

var queue = cq().process({ concurrency: 2 }, function (task, cb) {
    console.log(task + ' started')
    setTimeout(function () {
        cb(null, task)
    }, 1000)
})

for (var i = 1; i <= 10; i++) queue('task '+i, function (err, task) {
    console.log(task + ' done')
})

or with promises:

var cq = require('concurrent-queue')

var queue = cq().process({ concurrency: 2 }, function (task) {
    return new Promise(function (resolve, reject) {
        console.log(task + ' started')
        setTimeout(resolve.bind(undefined, task), 1000)
    })
})

for (var i = 1; i <= 10; i++) queue('task '+i).then(function (task) {
    console.log(task + ' done')
})

api

var cq = require('concurrent-queue')

var queue = cq(options)

Create a queue.

queue(item [, cb])

Push an item to the queue. Once the item has been processed, the optional callback will be executed with arguments determined by the processor.

Returns a promise that will be resolved or rejected once the item is processed.

queue.process([options, ] processor)

Configure the queue's processor function, to be invoked as concurrency allows with a queued item to be acted upon.

The optional options argument should be an object. It may contain a concurrency property that determines how many items in the queue will be processed concurrently. The default concurrency is Infinity.

The processor argument should be a function with signature function (item [, cb]). If the processor function signature included a callback, an error-first style callback will be passed which should be executed upon completion. If no callback is provided in the function signature, and the processor function returns a Promise, the item will be considered complete once the promise is resolved/rejected.

This function returns a reference to queue.

queue.items

An array of all queued items (both pending and processing).

queue.processing

An array of items currently being processed.

queue.pending

An array of items waiting to be processed.

queue.concurrency

An integer property representing the number of concurrent queue items that will be processed. This defaults to Infinity, but may be re-assigned. An integer value must be assigned to this property. This property may also be set by passing an options object to the process function (above) and specifying concurrency in that options object. To change concurrency after process is called, the new value must be assigned to this property. Setting this property to 0 will halt the queue (once all in-process items are complete), while setting it to Infinity removes all limits.

testing

npm test [--dot | --spec] [--coverage | --grep=pattern]

Specifying --dot or --spec will change the output from the default TAP style. Specifying --coverage will print a text coverage summary to the terminal after tests have ran, while --pattern will only run the test files that match the given pattern.

Open an html coverage report with npm run view-cover.