git ssb

1
const binarySearchInsert = require('binary-search-insert')
2
const SortedMap = require('sortedmap')
3
const LockMap = require('lockmap')
4
5
module.exports = class Scheduler {
6
  /**
7
   * The Scheduler manages the run cycle of the containers and figures out which
8
   * order they should run in
9
   */
10
  constructor () {
11
    this._waits = []
12
    this._running = new Set()
13
    this._loadingInstances = new LockMap()
14
    this.instances = new SortedMap(comparator)
15
    this.systemServices = new Map()
16
17
    function comparator (a, b) {
18
      return a.ticks - b.ticks
19
    }
20
  }
21
22
  /**
23
   * locks the scheduler from clearing waits untill the lock is resolved
24
   * @param {string} id
25
   * @return {function} the resolve function to call once it to unlock
26
   */
27
  lock (id) {
28
    return this._loadingInstances.lock(id)
29
  }
30
31
  /**
32
   * updates an instance with a new tick count
33
   * @param {Object} instance - a container instance
34
   */
35
  update (instance) {
36
    this._waits = this._waits.filter(wait => wait.id !== instance.id)
37
    this._update(instance)
38
    this._running.add(instance.id)
39
    this._checkWaits()
40
  }
41
42
  _update (instance) {
43
    this.instances.delete(instance.id)
44
    this.instances.set(instance.id, instance)
45
  }
46
47
  /**
48
   * returns a container
49
   * @param {String} id
50
   * @return {Object}
51
   */
52
  getInstance (id) {
53
    return this.instances.get(id) || this._loadingInstances.get(id) || this.systemServices.get(id)
54
  }
55
56
  /**
57
   * deletes an instance from the scheduler
58
   * @param {String} id - the containers id
59
   */
60
  done (id) {
61
    this._running.delete(id)
62
    this.instances.delete(id)
63
    this._checkWaits()
64
  }
65
66
  /**
67
   * returns a promise that resolves once all containers have reached the given
68
   * number of ticks
69
   * @param {interger} ticks - the number of ticks to wait
70
   * @param {string} id - optional id of the container that is waiting
71
   * @return {Promise}
72
   */
73
  wait (ticks, id) {
74
    this._running.delete(id)
75
    return new Promise((resolve, reject) => {
76
      binarySearchInsert(this._waits, comparator, {
77
        ticks: ticks,
78
        resolve: resolve,
79
        id: id
80
      })
81
      this._checkWaits()
82
    })
83
84
    function comparator (a, b) {
85
      return a.ticks - b.ticks
86
    }
87
  }
88
89
  /**
90
   * returns the oldest container's ticks
91
   * @return {integer}
92
   */
93
  syncLeastNumberOfTicks (exculde) {
94
    let ticks = 0
95
    for (const instance of this.instances) {
96
      ticks = instance[1].ticks
97
      if (instance[1].id !== exculde) {
98
        return ticks
99
      }
100
    }
101
    return ticks
102
  }
103
104
  // checks outstanding waits to see if they can be resolved
105
  async _checkWaits () {
106
    if (this._checkingWaits) {
107
      return
108
    } else {
109
      this._checkingWaits = true
110
      await [...this._loadingInstances.values()]
111
    }
112
    // if there are no running containers
113
    if (!this.instances.size) {
114
      // clear any remanding waits
115
      this._waits.forEach(wait => wait.resolve())
116
      this._waits = []
117
      this._checkingWaits = false
118
    } else {
119
      // find the old container and see if to can resolve any of the waits
120
      while (this._waits[0]) {
121
        const wait = this._waits[0]
122
        const least = this.syncLeastNumberOfTicks(wait.id)
123
        if (wait.ticks <= least) {
124
          this._waits.shift()
125
          wait.resolve()
126
          this._running.add(wait.id)
127
        } else {
128
          break
129
        }
130
      }
131
132
      if (!this._running.size && this._waits.length) {
133
        // if there are no containers running find the oldest wait and update
134
        // the oldest containers to it ticks
135
        const oldest = this._waits[0].ticks
136
        for (let instance of this.instances) {
137
          instance = instance[1]
138
          if (instance.ticks > oldest) {
139
            break
140
          } else {
141
            instance.ticks = oldest
142
            this._update(instance)
143
          }
144
        }
145
        this._checkingWaits = false
146
        return this._checkWaits()
147
      } else {
148
        this._checkingWaits = false
149
      }
150
    }
151
  }
152
}
153