Memolock JS

redis.js

import Redis from 'ioredis'

const {
  HOST: host,
  PORT: port,
} = process.env

const redis = new Redis({ host, port })

const subscribe = async (key, notifKey) => {
  const subclient = new Redis({ host, port })
  await subclient.subscribe(notifKey)
  // re-get in case we missed notifKey by a hair after lock attempt
  let value = await redis.get(key)
  if (!value) {
    value = await new Promise(resolve => {
      subclient.on('message', (channel, message) => {
        if (channel === notifKey) {
          resolve(message)
        }
      })
    })
  }
  await subclient.unsubscribe(notifKey)
  await subclient.disconnect()
  return value
}

export const memolock = async (key, ttl, generateValue) => {
  // FIXME: the value might be there, but considered stale because missing alive:key
  let value = await redis.get(key)
  if (!value) {
    const lockKey = `lock:${key}`
    const notifKey = `notif:${key}`
    const lock = await redis.set(lockKey, true, 'EX', ttl, 'NX')

    if (lock) {
      value = await generateValue()
      await redis
        .pipeline()
        .set(key, value, 'EX', ttl)
        .publish(notifKey, value)
        .exec()
    } else {
      value = await subscribe(key, notifKey)
    }
  }
  return value
}