Inter Process Object Sharing [IPOS]

Share objects across different Node.js processes. Write and read on both sides.
This package manages objects via IPC for you. When you create an object, it creates an equivalent on connected processes. When you update that object, it updates the equivalent accordingly. And if you delete the object, it will also delete the equivalent. This works both ways, so if you change the equivalent object in a subprocess, the original will be changes as well.

Install

npm i ipos

Usage

In the main process:

import child_process from 'child_process'
import IPOS from 'ipos'

// create a shared object instance
const sharedObject = IPOS.new()
// spawn a subprocess
// the ipc channel (4th stdio argument) is important
const subProcess = child_process.spawn('node', ['sub-process.js'], {
    stdio: ['inherit', 'inherit', 'inherit', 'ipc']
})
// register the subprocess with IPOS
// await: to wait for the connection to be established
await sharedObject.addProcess(subProcess)

In the subprocess:

import IPOS from 'ipos'

// await: to wait for the connection to be established (await only in subprocess)
const sharedObject = await IPOS.new()

See example/main-process.js and example/sub-process.js .

A note on class instances

To synchronise class instances, you first have to register the class with ipos on each process (on which the class instance does not yet exist) before the synchronisation happens. That means if you want to connect two IPOS instances, and the instance on the main process has a class instance somewhere inside a field, this class type must be registered on the subprocess, before calling IPOS.new(). For IPOS to be able to transmit the class instance it has to have methods to serialise (turn the class instance into either a string, a number, an object, an array, a map, or a set) and deserialize (turn the serialised value back into a class instance). IPOS will look for .serialize(), or .stringify() for serialisation and .from() for de-serialisation, but you can specify custom methods / functions. Here is an example:

// example-class.js

export class Example {
    data;

    constructor(data) {
        this.data = data
    }

    serialize() {
        return this.data
    }

    static from(data) {
        return new Example(data)
    }
}

// main-process.js

import IPOS from 'ipos'

const exampleInstance = new Example('myValue')
const ipos = IPOS.new()
ipos.create('myClassInstance', exampleInstance)
const subProcess = child_process.spawn('node', ['sub-process.js'], {
    stdio: ['inherit', 'inherit', 'inherit', 'ipc']
})
await sharedObject.addProcess(subProcess)

// sub-process.js

import IPOS from 'ipos'
import {Example} from './example-class.js'

const ipos = IPOS.registerClass(Example)
const ipos = await IPOS.new()

IPOS()

The main class. Don't use the new keyword (when creating an instance in a subprocess). Instead, use the static IPOS.new() method to create an instance.

static IPOS.new(config?: { syncTimeout: number }): IPOS | Promise<IPOS>

Creates a new instance. Multiple instances are not yet supported, so only create one instance per process. If it can synchronise with a parent process (i.e. process.send() exists), it will return a Promise which resolves after the synchronisation happened. Sometimes IPOS.new() is called in a subprocess but the parent process does not have an IPOS instance or has an IPOS instance but does not connect to the subprocess. Because of this, the promise returned by IPOS.new() resolves after 100ms without receiving a sync signal.

Parameters:

• config?: {} An optional config object with:
  • syncTimeout: number Time in milliseconds after which IPOS.new() auto-resolves

Returns:

• <IPOS> instance, if called in a normal process
• Promise<IPOS>, if called in a subprocess.
  Use await to wait for the connection to the main process to be established.

ipos.addProcess(process: ChildProcess): Promise<void>

Connect a subprocess to the IPOS instance. The subprocess must also call IPOS.new() for the two processes' IPOS to connect.

Parameters:

• process: ChildProcess The object of a subprocess IPOS should connect with. What gets returned by child_process.exec(), child_process.execFile(), child_process.fork(), or child_process.spawn()

Returns: Promise<void>. Use await to wait for the connection to the subprocess to be established.

ipos.removeProcess(process: ChildProcess): boolean

Disconnect a subprocess to the IPOS instance. Closed subprocess automatically get disconnected.

Parameters:

• process: ChildProcess The object of a subprocess IPOS should disconnect from. What gets returned by child_process.exec(), child_process.execFile(), child_process.fork(), or child_process.spawn()

Returns: boolean. true if a process was connected and has been disconnected, or false if the process was not connected.

ipos.create(key: string, value: any)

Create a field on the IPOS instance. This value can later be accessed or updated (See ipos.get()). After creating a field, you can access and update it (even change the type) with ipos[key: string] = value. See:

sharedObject.create('myValue', 23)
sharedObject.myValue = 'foo'
console.log(sharedObject.myValue) // -> 'foo'

ipos.create() can be called multiple times with the same key. Each time the old value will be overwritten.

Parameters:

• key: string A unique key.
• value: any The value to be stored.

ipos.get(key: string): any

Get an already created field from the IPOS instance. You can also use ipos[key: string] to access the value. If you use a method on the value that changes the value, this change will also be reflected in the connected IPOS instances. See:

sharedObject.create('myArray', [])
sharedObject.myArray.push('myString')
console.log(sharedObject.get('myArray')) // -> ['myString']
console.log(sharedObject.myArray) // -> ['myString']

And in a connected process, after 'myString' was pushed:

console.log(sharedObject.myArray) // -> ['myString']

Parameters:

• key: string A unique key of an already created field.

Returns: any. The stored value.

ipos.delete(key: string): boolean

Deletes the field with the specified key.

Parameters:

• key: string A unique key of an already created field.

Returns: boolean. true if a field existed and has been removed, or false if the element does not exist.

Testing

Glossary of terms

• "Synchronise" a field: Creating a main instance, then adding a field before connecting to a child instance. The field will be transmitted along with any other fields that may have been created during the connection process (synchronisation).
• "Create" a field: Creating a main instance, and connecting it to a child instance, then adding a field. The field will be transmitted on its own with a "set" message.
• "Reset" a field: Setting a field with a new value after it has been added and transferred. The field will be transmitted on its own with a "set" message.
• "Update" a field: Changing the value of a field after it has been added and transferred. This is only possible on fields with a value that is not immutable (i.e. objects, arrays, maps, sets, and class instances). The change and not the complete value will be transferred with an "update" message.
• "Delete" a field: Remove a field. The deletion will be communicated with a "delete" message.