Experiment with running concurrent processes with async.js, and writing dynamic log information to the terminal

async-experiment.js

var async = require('async');
require('colors');

var CONCURRENCY = 5;
var S_BUILDING  = ' Building '.bold;
var S_BUILT     = ' Built    '.green.bold;

function buildIt() {
    console.log("Starting process with concurrency of ", CONCURRENCY);

    // stream for building
    // runs a build for a single bundleCfg object
    var build$ = async.queue(function (bundleCfg, done) {
        var builder = new jspm.Builder();

        bundleCfg.status = S_BUILDING;
        log$.push(bundleCfg);

        setTimeout(function () {
            bundleCfg.status = S_BUILT;
            log$.push(bundleCfg);
            done(null, bundleCfg);
        }, Math.floor(Math.random()*10000));
    }, CONCURRENCY);

    // stream for log writing to console
    // there can only be one of these, since it writes escape strings to move
    // up to the line it needs to print on, and then prints that line
    var logLine = 1;
    var log$ = async.queue(function (bundleCfg, done) {
        if (!bundleCfg._logLine) {
            bundleCfg._logLine = logLine++;
            process.stdout.write('\n');
        }

        // go up from current line to the line this bundle is on
        for (var i = logLine; i!=bundleCfg._logLine;i--) {
            process.stdout.write("\x1b[A\r");
        }
        process.stdout.write(bundleCfg.status + ' ' + bundleCfg.name);
        // step back down to logline from the bundle's logline
        for (;i<logLine;i++) {
            process.stdout.write("\n");
        }
        done();
    }, 1);

    [
        {name: 'aaa'},
        {name: 'bbb'},
        {name: 'ccc'},
        {name: 'ddd'},
        {name: 'eee'},
        {name: 'fff'},
        {name: 'ggg'},
        {name: 'hhh'},
        {name: 'iii'},
        {name: 'jjj'},
        {name: 'kkk'},
        {name: 'lll'},
        {name: 'mmm'},
        {name: 'nnn'},
        {name: 'ooo'},
        {name: 'ppp'},
        {name: 'qqq'},
        {name: 'rrr'},
        {name: 'sss'},
        {name: 'ttt'},
        {name: 'uuu'}
    ].forEach(function (bundleCfg) {
        build$.push(bundleCfg, function (err, result) {
            if (err) { throw err; }
        });
    });
}

gulp.task('do', function () {
    buildIt();
});