Cancel token for invoke-parallel

invoke-parallel-cancel-token.js

// This holds all the real state
class CancelController {
  constructor(init) {
    this._canceled = false
    this._token = undefined
    this._promise = undefined
    this._cancels = undefined
    this._resolve = undefined
  }

  get isCanceled() {
    return this._canceled
  }

  get token() {
    return this._token || (this._token = new CancelToken(this))
  }

  cancel() {
    if (!this._canceled) {
      this._canceled = true
      const cancels = this._cancels
      if (this._resolve != null) this._resolve()
      this._resolve = undefined
      this._cancels = undefined
      if (cancels != null) cancels.forEach(cancel => cancel())
    }
  }

  cancelAsync() {
    if (!this._canceled) {
      this._canceled = true
      const cancels = this._cancels
      const p = Promise.resolve()
      if (this._resolve != null) p.then(this._resolve)
      if (cancels != null) p.then(() => cancels.forEach(cancel => cancel()))
      this._resolve = undefined
      this._cancels = undefined
    }
  }
}

// Proxy for the controller, to provide privacy. Not directly exposed.
class CancelToken {
  constructor(ctrl) {
    this._ = ctrl
  }

  get isCanceled() {
    return this._._canceled
  }

  get promise() {
    return this._._promise || (this._._promise = new Promise(resolve => {
      if (!this._._canceled) this._._resolve = resolve
    }))
  }

  throwIfCanceled() {
    if (this._._canceled) throw new Cancel()
  }

  addCancel(func) {
    if (this._._canceled) return
    if (this._._cancels == null) this._._cancels = new Set()
    this._._cancels.add(func)
  }

  removeCancel(func) {
    if (this._._cancels != null) this._._cancels.remove(func)
  }
}