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							- 'use strict'
 
- module.exports = RunQueue
 
- var validate = require('aproba')
 
- function RunQueue (opts) {
 
-   validate('Z|O', [opts])
 
-   if (!opts) opts = {}
 
-   this.finished = false
 
-   this.inflight = 0
 
-   this.maxConcurrency = opts.maxConcurrency || 1
 
-   this.queued = 0
 
-   this.queue = []
 
-   this.currentPrio = null
 
-   this.currentQueue = null
 
-   this.Promise = opts.Promise || global.Promise
 
-   this.deferred = {}
 
- }
 
- RunQueue.prototype = {}
 
- RunQueue.prototype.run = function () {
 
-   if (arguments.length !== 0) throw new Error('RunQueue.run takes no arguments')
 
-   var self = this
 
-   var deferred = this.deferred
 
-   if (!deferred.promise) {
 
-     deferred.promise = new this.Promise(function (resolve, reject) {
 
-       deferred.resolve = resolve
 
-       deferred.reject = reject
 
-       self._runQueue()
 
-     })
 
-   }
 
-   return deferred.promise
 
- }
 
- RunQueue.prototype._runQueue = function () {
 
-   var self = this
 
-   while ((this.inflight < this.maxConcurrency) && this.queued) {
 
-     if (!this.currentQueue || this.currentQueue.length === 0) {
 
-       // wait till the current priority is entirely processed before
 
-       // starting a new one
 
-       if (this.inflight) return
 
-       var prios = Object.keys(this.queue)
 
-       for (var ii = 0; ii < prios.length; ++ii) {
 
-         var prioQueue = this.queue[prios[ii]]
 
-         if (prioQueue.length) {
 
-           this.currentQueue = prioQueue
 
-           this.currentPrio = prios[ii]
 
-           break
 
-         }
 
-       }
 
-     }
 
-     --this.queued
 
-     ++this.inflight
 
-     var next = this.currentQueue.shift()
 
-     var args = next.args || []
 
-     // we explicitly construct a promise here so that queue items can throw
 
-     // or immediately return to resolve
 
-     var queueEntry = new this.Promise(function (resolve) {
 
-       resolve(next.cmd.apply(null, args))
 
-     })
 
-     queueEntry.then(function () {
 
-       --self.inflight
 
-       if (self.finished) return
 
-       if (self.queued <= 0 && self.inflight <= 0) {
 
-         self.finished = true
 
-         self.deferred.resolve()
 
-       }
 
-       self._runQueue()
 
-     }, function (err) {
 
-       self.finished = true
 
-       self.deferred.reject(err)
 
-     })
 
-   }
 
- }
 
- RunQueue.prototype.add = function (prio, cmd, args) {
 
-   if (this.finished) throw new Error("Can't add to a finished queue. Create a new queue.")
 
-   if (Math.abs(Math.floor(prio)) !== prio) throw new Error('Priorities must be a positive integer value.')
 
-   validate('NFA|NFZ', [prio, cmd, args])
 
-   prio = Number(prio)
 
-   if (!this.queue[prio]) this.queue[prio] = []
 
-   ++this.queued
 
-   this.queue[prio].push({cmd: cmd, args: args})
 
-   // if this priority is higher than the one we're currently processing,
 
-   // switch back to processing its queue.
 
-   if (this.currentPrio > prio) {
 
-     this.currentQueue = this.queue[prio]
 
-     this.currentPrio = prio
 
-   }
 
- }
 
 
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