let listenInBackground, sendPings const redis = require('@overleaf/redis-wrapper') const rclient1 = redis.createClient({ cluster: [ { port: '7000', host: '127.0.0.1', }, ], }) const rclient2 = redis.createClient({ cluster: [ { port: '7000', host: '127.0.0.1', }, ], }) let counter = 0 const sendPing = function (cb) { if (cb == null) { cb = function () {} } return rclient1.rpush('test-blpop', counter, error => { if (error != null) { console.error('[SENDING ERROR]', error.message) } if (error == null) { counter += 1 } return cb() }) } let previous = null const listenForPing = cb => rclient2.blpop('test-blpop', 200, (error, result) => { if (error != null) { return cb(error) } let [, value] = Array.from(result) value = parseInt(value, 10) if (value % 10 === 0) { console.log('.') } if (previous != null && value !== previous + 1) { error = new Error( `Counter not in order. Got ${value}, expected ${previous + 1}` ) } previous = value return cb(error, value) }) const PING_DELAY = 100 ;(sendPings = () => sendPing(() => setTimeout(sendPings, PING_DELAY)))() ;(listenInBackground = () => listenForPing(error => { if (error) { console.error('[RECEIVING ERROR]', error.message) } return setTimeout(listenInBackground) }))()