mprocess.js

Simple ChildProcess module wrapper

NodeJS has great module that handle creating, manipulating, and destroying child processes using simple module called Child Process (https://nodejs.org/api/child_process.html). Personally, I think Child Process module compensates javascript single-threaded nature when an application needs to consume more CPU power explicitly. MProcess was developed when I need to send commands to child processes and retrieve the responses. Although this functionality is already managed by Child Process .send(), but it lacks state management when a parent process send several commands / messages to several child processes. MProcess works well on maintaining the state of a message ("tell which message is responding which command"). Currently, MProcess only wraps spawn() and fork() method.

Installation

$ npm install mprocess

API

Constructor

MProcess(command[,args,][, type][, options])

Parameters

• command : The command to run
• args : Array of arguments for command. Default to empty array
• type : Type of runner. Currently support MProcess.FORK to invoke fork or MProcess.SPAWN to invoke spawn. Default to MProcess.SPAWN
• options : Object containing parameter that will control the behaviour of invoked process. Accept all parameter defined in https://nodejs.org/api/child_process.html. Default to {}

Return

MProcess Object

Methods

• run()
  After creating new MProcess, the process itself is not automatically created. To create the process, invoke run()
• kill([code])
  Kill the underlying process. Custom signal can ben passed to child process via code
• done(fn)
  Receive callback as parameter that is invoked when the child process is exited.
  • fn(ret)
ret could be an integer with 0 value, or an object containing code and signal if the child process not cleanly exited
• clone()
  Create new MProcess object based on current instance of MProcess
• send(messsage)
  Send message to child process. Note that send() can only be used if MProcess instance is initiated using MProcess.FORK type. Return Promise and will resolve if child process successfully response, and reject if child process can't response in timely fashion.
• getProcess()
  Return ChildProcess object of the current instance of MProcess or null if run() has not been called previously.
• onStdOutFinish(fn)
  Receive callback as parameter that is invoked when the child process finish streaming its standard output. Callback not fired if you supply options during instantiation with {stdio : 'inherit'}
  • fn(str)
str contains the output string
• onStdOutError(fn)
  Receive callback as parameter that is invoked when the child process experience errors and writing to its std err. Callback not fired if you supply options during instantiation with {stdio : 'inherit'}
  • fn(str)
str contains the error string

How to use

SPAWN

var MProcess = require("mprocess")
var processPath = "/path/to/some/javascript/file"
var instance = new MProcess("node",[processPath],MProcess.SPAWN);
instance.run()
instance.done(function(code){
    //code == 0
}) 

FORK

main.js

var MProcess = require("mprocess")
var processPath = "/path/to/some/worker/file"
var instance = new MProcess("node",[processPath],MProcess.FORK);
instance.run()
instance.send("here my message").then(function(resp){
    // resp contains valid javascript object
}).catch(console.error)
instance.done(function(code){
    //code == 0
}) 

To be able answer on parent process send(), the worker script must able to do this :

process.on("message",function(message){
    var id = message.id; // message id, internally created by MProcess
    var data = message.data; // will contains 'here my message'
    // some process
    var response = {valid javascript object}
    process.send({
        id : id,
        data : response
    })
})

GitHub

https://github.com/aerios/mprocess