Singleton process via sockets

README.md

Singleton Process

An application that manages singleton process.

It will print any cli arguments used when executing additonal instances of the application.

Example

$ node SingletonApplication.js
$ Starting: first Application instance
$ Listening for additional Application instances...

And in another terminal instance

$ node SingletonApplication.js --Hello "World"
$ Starting: additional Application instance
$
$   ...Sent args to first Application
$
$ Finishing: additional Application instance

The first terminal instance will produce extra lines

$ Arguments accepted:
$   { _: [], Hello: 'World', '$0': 'SingletonApplication.js' }

SingletonApplication.js

var os   = require('os');
var fs   = require('fs');
var net  = require('net');
var path = require('path');
var argv = require('yargs').argv;

// Singleton process class.
//
// When first run, this Application will remain open, listening for additional
// Applications that are executed elsewhere in the system. Additional Applications
// will send their cli arguments to the first Application before closing themselves.
function Application(args) {
    var self = this;
    self.socketPath = path.join(os.tmpdir(), "atom-"+process.env.USER+".sock");

    // Additional Application's will connect.
    self.client = net.connect({path: self.socketPath}, self.handleAdditionalApplication.bind(this, args));
    // The first Application will fail at connecting, instead starting the server
    // for additional Application's to connect onto.
    self.client.on('error', self.listenForArgumentsFromNewProcess.bind(this));
}

Application.prototype.handleAdditionalApplication = function(args) {
    console.log('Starting: additional Application instance')
    var self = this;
    this.passArgsToServer(args)
}

Application.prototype.passArgsToServer = function(args) {
    var self = this;

    self.client.write(JSON.stringify(args), function() {
        console.log('\n  ...Sent args to first Application\n')
        self.client.end();
        console.log('Finishing: additional Application instance')
        process.exit();
    })
}

/**
 * The master application process will run a socket server to accept arguments
 * from additional processes.
 */
Application.prototype.listenForArgumentsFromNewProcess = function() {
    console.log('Starting: first Application instance')
    var self = this;

    // Clean
    self.unlinkSocketFile()

    var server = net.createServer(function(connection) {
        connection.on('data', function(data) {
            self.printArguments(JSON.parse(data))
        })
    });

    console.log('Listening for additional Application instances...')
    server.listen(self.socketPath);
    server.on('error', function(err) {
        console.error('Application server failed', err);
    });
}

/**
 * Removes our applications socket file.
 */
Application.prototype.unlinkSocketFile = function() {
    var self = this;

    if (process.platform == 'win32') {
        return;
    } else {
        if (fs.existsSync(self.socketPath)) {
            try {
                fs.unlinkSync(self.socketPath)
            } catch (e) {
                throw e;
            }
        }
    }
}

Application.prototype.printArguments = function(args) {
    console.log("Arguments accepted:\n", args)
}

var app = new Application(argv);