admin管理员组

文章数量:1277875

Is it possible to call multiple functions at the same time?

E.g.

var executed = false;
// loop 1
func();
// loop 2
func();

function func(){
    if (executed) return;
    executed = true;
    alert(1);
}

Can func() be executed 2 times at once?

Is it possible to call multiple functions at the same time?

E.g.

var executed = false;
// loop 1
func();
// loop 2
func();

function func(){
    if (executed) return;
    executed = true;
    alert(1);
}

Can func() be executed 2 times at once?

  • javascript
  • multithreading
Share Improve this question edited Sep 28, 2018 at 9:54 jan-seins 1,2931 gold badge19 silver badges35 bronze badges asked Jun 9, 2017 at 19:56 user234user234 1091 gold badge1 silver badge9 bronze badges 12
  • 3 Javascript is like most programming languages, everything is executed in order, unless you explicitly use something that runs asynchronously or uses threads (e.g. Javascript WebWorkers). – Barmar Commented Jun 9, 2017 at 19:58
  • 1 When you write func(); func();, it doesn't execute the second call until the first call returns. – Barmar Commented Jun 9, 2017 at 19:59
  • @Barmar unless they are async – Paul Commented Jun 9, 2017 at 20:00
  • 2 JavaScript has no (standard) provision for concurrent execution contexts (ie. "threads") that can interact. Asynchronicity and concurrency are different. Therefore, "at the same time" should be better qualified. – user2864740 Commented Jun 9, 2017 at 20:00
  • Node JS is the closest thing I know of to true async – Stephen J Commented Jun 9, 2017 at 20:01
 |  Show 7 more ments

4 Answers 4

Reset to default 4

JavaScript has no native support for running multiple functions simultaneously. It has, historically, depended on time-consuming tasks (such as waiting for an HTTP request or doing something CPU intensive) being handled with native code that presents an API to JS (and that API accepting a callback or, more recently, returning a Promise).

That is starting to change.

Most web browsers support Web Workers and Node.js has introduced experimental support for Worker Threads.

These each allow JavaScript code to be farmed off to a separate process which runs independently of the main event loop and municate with the main process using messages.

No processor i know can execute statements at the same time. Most puters have multiple processors, so they can run multiple statements on multiple processors. So the only possible solution would be opening your browser twice, open the same page and hope that the js is executed parallel ( or use some fancy NodeJS or WebWorkers etc.).

However instead of running the same time , its mon to switch between two threads very fast, so that it looks like being the same time (called multitasking). You could do this in js like this:

var executed = false;
var theother=new Promise( r=>setTimeout(r,0));
func();
// loop 2
func();

async function func(){
if (executed) return;
await theother;
executed = true;
alert(1);
}

Or old style ( to resolve the magic ):

var executed = false;
// loop 1
func();
// loop 2
func();

function func(){
if (executed) return;
setTimeout(function(){
  executed = true;
  alert(1);
 },0);
}

You can't do this. Because JavaScript does not support multi-threading. Every tab of web browser just have a single interpreter and JavaScript interpreter in the browser is a single thread. See an example of single thread here.

See also this answer.

Use below code

<!DOCTYPE html>
<html>
<head>
    <title>sample test</title>
    <script type="text/javascript">

        print=function(msg) {
            var ifunction=function(){
                console.log(msg);
            }
            return ifunction;
        };

        button1=function(name,count){
                for (var i =0 ;i <count; i++) {
                    setTimeout(print(name+":"+i+"seconds over after button1 click"),i*500);
                }
        };

    </script>
</head>
<body>
    <form>
        <input type="" name="" />
        <input type="button" value="button1" onclick="button1('button1',5)" />
        <input type="button" value="button2" onclick="button1('button2',5)" />
    </form>
</body>
</html>

本文标签： multithreadingCan javascript run multiple functions at onceStack Overflow

版权声明：本文标题：multithreading - Can javascript run multiple functions at once? - Stack Overflow 内容由网友自发贡献，该文观点仅代表作者本人， 转载请联系作者并注明出处：http://www.betaflare.com/web/1741303914a2371256.html， 本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌抄袭侵权/违法违规的内容，一经查实，本站将立刻删除。