sequencialize

Run async functions in sequence. Queue async functions.

How to make parallel-running async function run sequencially? This module tries to resolve the problem when something like findAndUpdate creates two entries when run almost parallel.

So, we just chain them.

If you are using message broker to queue potentially-breaking parallel function calls, you won't need this.

Usage

const Sequencer = require('sequencialize')
const sequencer = new Sequencer()

await sequencer.run(func:Function, [namespace:String])

It will return the value returned from the original function. So:

const n = 3
const func = async n => n

for(let i = n;i;i--){
  sequencer
    .run(() => func(i))
    .then(v => console.log(v))
}

// 3
// 2
// 1

It will run functions in sequence:

const wait = t => new Promise(r => setTimeout(r,t))
const n = 3
const func = n => {
  return wait(1000+ Math.random() * 5000)
    .then(() => console.log(n))
}

for(let i = n;i;i--){
  sequencer.run(() => func(i))
}

// 3
// 2
// 1

you can use namespace. Each namespace is it's own sequence:

const wait = t => new Promise(r => setTimeout(r,t))
const n = 3
const func = (namespace, n) => {
  return wait(1000+ Math.random() * 5000)
    .then(() => console.log(`${namespace}: ${n}`))
}

for(let i = n;i;i--){
  sequencer.run(() => func('asdf', i), 'asdf')
  sequencer.run(() => func('ASDF', i), 'ASDF')
}

// each function in a namespace runs in sequence
// asdf: 3
// ASDF: 3
// asdf: 2
// asdf: 1
// ASDF: 2
// ASDF: 1

Use Case

instead of this:

// potentially racing
const handleRequest = () => {

  db.longCalculationAndUpsert({
    where: { user_id },
    data
  })

}

write this:

// run in sequence for every user_id
const handleRequest = () => {

  sequencer.run(() => {
    return db.longCalculationAndUpsert({
      where: { user_id },
      data
    })
  }), user_id)

}

Cheers, juji