# all files / lib/spdy-transport/protocol/base/ scheduler.js

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88.24% Branches 30/34
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100% Lines 106/106

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     'use strict'

    var transport = require('../../../spdy-transport')
    var utils = transport.utils

    var assert = require('assert')
    var util = require('util')
    var debug = require('debug')('spdy:scheduler')
    var Readable = require('readable-stream').Readable

    /*
     * We create following structure in `pending`:
     * [ [ id = 0 ], [ id = 1 ], [ id = 2 ], [ id = 0 ] ]
     *     chunks      chunks      chunks      chunks
     *     chunks                  chunks
     *     chunks
     *
     * Then on the `.tick()` pass we pick one chunks from each item and remove the
     * item if it is empty:
     *
     * [ [ id = 0 ], [ id = 2 ] ]
     *     chunks      chunks
     *     chunks
     *
     * Writing out: chunks for 0, chunks for 1, chunks for 2, chunks for 0
     *
     * This way data is interleaved between the different streams.
     */

    function Scheduler (options) {
      Readable.call(this)

      // Pretty big window by default
      this.window = 0.25

      Iif (options && options.window) { this.window = options.window }

      this.sync = []
      this.list = []
      this.count = 0
      this.pendingTick = false
    }
    util.inherits(Scheduler, Readable)
    module.exports = Scheduler

    // Just for testing, really
    Scheduler.create = function create (options) {
      return new Scheduler(options)
    }

    function insertCompare (a, b) {
      return a.priority === b.priority
        ? a.stream - b.stream
        : b.priority - a.priority
    }

    Scheduler.prototype.schedule = function schedule (data) {
      var priority = data.priority
      var stream = data.stream
      var chunks = data.chunks

      // Synchronous frames should not be interleaved
      if (priority === false) {
        debug('queue sync', chunks)
        this.sync.push(data)
        this.count += chunks.length

        this._read()
        return
      }

      debug('queue async priority=%d stream=%d', priority, stream, chunks)
      var item = new SchedulerItem(stream, priority)
      var index = utils.binaryLookup(this.list, item, insertCompare)

      // Push new item
      if (index >= this.list.length || insertCompare(this.list[index], item) !== 0) {
        this.list.splice(index, 0, item)
      } else { // Coalesce
        item = this.list[index]
      }

      item.push(data)

      this.count += chunks.length

      this._read()
    }

    Scheduler.prototype._read = function _read () {
      if (this.count === 0) {
        return
      }

      if (this.pendingTick) {
        return
      }
      this.pendingTick = true

      var self = this
      process.nextTick(function () {
        self.pendingTick = false
        self.tick()
      })
    }

    Scheduler.prototype.tick = function tick () {
      // No luck for async frames
      Iif (!this.tickSync()) { return false }

      return this.tickAsync()
    }

    Scheduler.prototype.tickSync = function tickSync () {
      // Empty sync queue first
      var sync = this.sync
      var res = true
      this.sync = []
      for (var i = 0; i < sync.length; i++) {
        var item = sync[i]
        debug('tick sync pending=%d', this.count, item.chunks)
        for (var j = 0; j < item.chunks.length; j++) {
          this.count--
          res = this.push(item.chunks[j])
        }
        debug('after tick sync pending=%d', this.count)

        // TODO(indutny): figure out the way to invoke callback on actual write
        if (item.callback) {
          item.callback(null)
        }
      }
      return res
    }

    Scheduler.prototype.tickAsync = function tickAsync () {
      var res = true
      var list = this.list
      if (list.length === 0) {
        return res
      }

      var startPriority = list[0].priority
      for (var index = 0; list.length > 0; index++) {
        // Loop index
        index %= list.length
        if (startPriority - list[index].priority > this.window) { index = 0 }
        debug('tick async index=%d start=%d', index, startPriority)

        var current = list[index]
        var item = current.shift()

        if (current.isEmpty()) {
          list.splice(index, 1)
          if (index === 0 && list.length > 0) {
            startPriority = list[0].priority
          }
          index--
        }

        debug('tick async pending=%d', this.count, item.chunks)
        for (var i = 0; i < item.chunks.length; i++) {
          this.count--
          res = this.push(item.chunks[i])
        }
        debug('after tick pending=%d', this.count)

        // TODO(indutny): figure out the way to invoke callback on actual write
        if (item.callback) {
          item.callback(null)
        }
        Iif (!res) { break }
      }

      return res
    }

    Scheduler.prototype.dump = function dump () {
      this.tickSync()

      // Write everything out
      while (!this.tickAsync()) {
        // Intentional no-op
      }
      assert.equal(this.count, 0)
    }

    function SchedulerItem (stream, priority) {
      this.stream = stream
      this.priority = priority
      this.queue = []
    }

    SchedulerItem.prototype.push = function push (chunks) {
      this.queue.push(chunks)
    }

    SchedulerItem.prototype.shift = function shift () {
      return this.queue.shift()
    }

    SchedulerItem.prototype.isEmpty = function isEmpty () {
      return this.queue.length === 0
    }