medium/lib/buffers.js

CSP-style channel library using ES7 async/await keywords

const base = () => ({
	unreleased: [],
	push(put) {
		this.unreleased.push(put)
	},
	shift() {
		return this.unreleased.shift()
	},
	isEmpty() { return !this.unreleased.length }
})

const fixed = limit => ({
	unreleased: [],
	released: [],
	release(put) {
		this.released.push(put)
		put.resolve(true)
	},
	push(put) {
		if (this.released.length === limit) {
			this.unreleased.push(put)
		} else {
			this.release(put)
		}
	},
	shift() {
		if (!this.released.length) return

		var next = this.released.shift()

		var waiting = this.unreleased.shift()
		if (waiting) this.release(waiting)

		return next
	},
	isEmpty() { return !this.released.length }
})

const dropping = limit => ({
	released: [],
	push(put) {
		if (this.released.length < limit) {
			this.released.push(put)
		}
		put.resolve(true)
	},
	shift() {
		return this.released.shift()
	},
	isEmpty() { return !this.released.length }
})

const sliding = limit => ({
	released: [],
	push(put) {
		if (this.released.length === limit) {
			this.released = this.released.slice(1).concat([ put ])
		} else {
			this.released.push(put)
		}
		put.resolve(true)
	},
	shift() {
		return this.released.shift()
	},
	isEmpty() { return !this.released.length }
})

const throttled = ms => ({
  alwaysUse: true,
  unreleased: [],
  released: [],
  buffer: null,
  run: null,
  polling: false,
  intervalRef: null,
  ensurePolling() {
    if (this.intervalRef !== null) return

    this.intervalRef = setInterval(() => {
      this.process()
      if (!this.unreleased[0]) {
        clearInterval(this.intervalRef)
        this.intervalRef = null
      }
    }, ms)
  },
  process() {
    if (this.unreleased[0]) {
      const put = this.unreleased.shift()
      this.released.push(put)
      put.resolve(true)
      const take = this.channel.takes.shift()
      if (take) this.run(this.channel, put, take)
    }
  },
  push(put) {
    this.unreleased.push(put)
    this.ensurePolling()
  },
  shift() {
    return this.released.shift()
  },
  isEmpty() { !this.released.length && !this.unreleased.length }
})

module.exports = { base, fixed, dropping, sliding, throttled }