cpuse: cpu monitor for node

cpuse.js

//
// cpuse.js - simple continuous cpu monitor for node
//
// Intended for programs wanting to monitor and take action on overall CPU load.
//
// The monitor starts as soon as you require the module, then you can query it at
// any later time for the average cpu:
//
// > var cpuse = require('cpuse');
// > cpuse.averages();
// { '1 second': 0.041688434470403546,
//  '10 second': 0.048103193628717615,
//  '1 minute': 0.051149340772080894,
//  '5 minute': 0.05174290700985427,
//  '30 minute': 0.051857909889630564,
//  '1 hour': 0.05188362865090424 }
//
// The numbers are exponentially weighted moving averages over the given period.
//

var os = require('os');

var load = 0;
var last = { user: 0, nice: 0, sys: 0, idle: 0, irq: 0 };
var last_update = new Date;

var smooth_data = {
      '1 second': {
          ms: 1000
        , load: 0
    }
    , '10 second': {
          ms: 1000*10
        , load: 0
    }
    , '1 minute': {
          ms: 1000*60
        , load: 0
    }
    , '5 minute': {
          ms: 1000*300
        , load: 0
    }
    , '30 minute': {
          ms: 1000*1200
        , load: 0
    }
    , '1 hour': {
          ms: 1000*3600
        , load: 0
    }
};

var update_cpus = function(first) {

    var cpus = os.cpus();
    var total = { user: 0, nice: 0, sys: 0, idle: 0, irq: 0 };
    //console.log(cpus);

    // Aggregate ticks from all cpus
    for (var i=0; i < cpus.length; i++) {
        cpu = cpus[i];
        total.user += cpu.times.user;
        total.nice += cpu.times.nice;
        total.sys += cpu.times.sys;
        total.idle += cpu.times.idle;
        total.irq += cpu.times.irq;
    }
    //console.log(total);

    // Figure out how they changed since last time
    var diff = {
          user: total.user - last.user
        , nice: total.nice - last.nice
        , sys:  total.sys  - last.sys
        , idle: total.idle - last.idle
        , irq:  total.irq  - last.irq
    };

    // Calculate load
    var all = (diff.user + diff.nice + diff.sys + diff.idle + diff.irq);
    load = (all - diff.idle) / all;

    //
    // Average load using equation:
    // AVG[n] = alpha * OBS[n] + (1 - alpha) * AVG[n-1]
    // where alpha = 1 - e^-( (T[n]-T[n-1]) / AVERAGE_PERIOD )
    //
    var now = new Date
    var diff_ms = now - last_update;
    for (var interval in smooth_data) {
        var alpha = 1 - Math.exp( - diff_ms / smooth_data[interval].ms );
        if (first) smooth_data[interval].load = load;
        else smooth_data[interval].load = alpha * load + (1-alpha) * smooth_data[interval].load;
    }
    last_update = now;

    // Update state for next time
    last = total;

}

update_cpus(true);
setInterval(update_cpus, 1000);

var averages = function() {
    var data = {};
    for (var interval in smooth_data) data[interval] = smooth_data[interval].load;
    return data;
}

if (require.main === module) {
    setInterval(function() {
        console.log(averages());
    }, 1000);
} else {
    exports.averages = averages;
}