System library

Note Content

• Print text to the system console
  • Example print() and println()
• Memory, System time
  • Example memory operations, system time
• Multithreading
  • Example with function
  • Example with Object's method .run()
• Timers
  • Example timeout()

System library provides functionality as system output, multithreading control and timers.

Initialize:

var system = require('system');

Print text to the system console

These functions provides text output to system console - standard output

println (text);

String text - print text to system console and append new line

print (text);

String text - print text to system console without new line

Example print() and println()

var system = require('system');
var text = "some text to output";
system.print("this is ");
system.println(text);

Memory, System time

Number freemem();

Returns free memory amount in bytes.

Number totalmem ();

Returns total memory amount in bytes.

Number currentTimeInMillis ();

returns the difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.

Example memory operations, system time

var sys = require('system');
var totalMemory = sys.totalmem();
var freeMemory = sys.freemem();
var timeStamp = sys.currentTimeInMillis();
sys.println("Total memory:"+totalMemory+" free memory:"+freeMemory);
sys.println("Time in milliseconds:"+(sys.currentTimeInMillis()-timeStamp);

Multithreading

This functionality provides thread creating.

runAsThread(threadName, func, callback);

String threadName - name of thread.

function | Object funct - function funct will be launched in new thread with identification as threadName.

function callback - function or run method of Object will be invoked (from event loop) when function funct will be done.

sleep (delay);

Number delay - function does pause of program or thread for delay in milliseconds.

Warning Do not use sleep() in main thread (loop). It will block event loop.

Example with function

var sys = require('system');
var myfunc = function(){
    for (i=0;i<20;i++){
        sys.println("tick");
        sys.sleep(1000);
    }
    return "done";
}

sys.runAsThread("mythread", myfunc,function(result){
    sys.println("Thread is "+result);
});

Example with Object's method .run()

var sys = require('system');
var Ticker = function(){
    this.interval = 1000;
    this.run = function(){
        var count = 0;
        while(count<30){
            sys.println("tick");
            sys.sleep(this.interval);
            count++;
        }
        return "done";
    }
}
//create ticker object
var ticker = new Ticker();
sys.runAsThread("mythread", ticker,function(result){
    sys.println("Thread is "+result);
});

Timers

Timeout is asynchronous timed function.

setTimeout (func, timeout);

Function func - Function will be once launch after timeout once time. Number timeout - timeout in milliseconds

setTimeout (func, timeout, repeats);

Function func - Function will be repeated with period defined by timeout.

Number timeout - Time in millisecond.

Number repeats - Number of repeats is defined by repeats. 0 = always.

Example timeout()

var sys = require('system');
//only one after 2 sec.
sys.setTimeout(function(){
        sys.println("only one tik")
    },2000);

//forever
sys.setTimeout(function(){
        sys.println("tik2")
    },2000,0);

//repeat 5 times with 1 second period
sys.setTimeout(function(){
        sys.println("tik2")
    },1000,5);