Anonymous functions garbage collection - nodejs

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Message from discussion Anonymous functions garbage collection
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Date: Thu, 13 Sep 2012 18:03:50 +0530
From: Vinayak Mishra <vnykm...@gmail.com>
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Subject: Re: [nodejs] Anonymous functions garbage collection
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I don't see any problem with your approach, and I would probably have 
done the same. Yet, JSLint would remind about making functions within 
loop. Well, should not matter unless you're looping over arrays with 
/some/ thousands elements.

As an alternative, if code readability/simplicity is a concern, why not 
go with async <https://github.com/caolan/async>?

var execute = function (item, cb) {
/* do something meaningful with item, fire cb when done */
   };

var arr = getInitialData();
async.forEach(arr, execute, function (err) {
   // check for error and/or proceed further
});

You could use one of many available control flows, check out many more 
control flows <https://github.com/caolan/async/blob/master/README.md>. 
The advantage is the package provides different control flows without 
having to keep re-inventing them. Say, you want to perform certain 
activity in parallel, or in series, or based on some conditionals, while 
we could write code to achieve that, I would recommend using async as it 
is well written and thoroughly tested <https://npmjs.org/package/async> 
piece of code.

Where you want to place the execute code depends on many factors, like 
do we need to access/modify other variables in scope, if independent 
operations, they can go in library functions.

Please share your thoughts.


On 09/13/2012 11:30 AM, Maxim Kazantsev wrote:
> It is a pretty typical approach to use an anonymous function for 
> asynchronous calls from inside a loop:
>
>     var a = getInitialData();
>     for (var i = 0, len = a.length; i < len; i++) {
>       (function(el) {
>         /* do something non-blocking here */
>       })(a[i]);
>     }
>
>
> JSLint doesn't like this code with "Don't make functions within a 
> loop" warning, and it is actually right since it really creates a new 
> anonymous function on every single loop iteration. An obvious solution 
> is to declare this function outside a loop, but it would make a code 
> less readable. Even if a declaration would just precede the loop: you 
> see a call here, you see a declaration somewhere else, and here you 
> are, lost all your attention.
>
> My question is how bad this approach is for an overall performance? In 
> particular, how fast and efficient a garbage collection of anonymous 
> functions is? How much memory a typical anonymous function can consume 
> and how long it may exist in a memory?
> -- 
> Job Board: http://jobs.nodejs.org/
> Posting guidelines: 
> https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines
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-- 
Regards,
Vinayak


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    I don't see any problem with your approach, and I would probably
    have done the same. Yet, <tt>JSLint</tt> would remind about making
    functions within loop. Well, should not matter unless you're looping
    over arrays with <i>some</i> thousands elements.<br>
    <br>
    As an alternative, if code readability/simplicity is a concern, why
    not go with <tt><a href="https://github.com/caolan/async">async</a></tt>?<br>
    <br>
    <tt>var execute = function (item, cb) {</tt><tt><br>
    </tt><tt>&nbsp; </tt><tt>/* do something meaningful with item, fire cb
      when done */</tt><tt><br>
    </tt><tt>&nbsp; };</tt><tt><br>
    </tt><tt><br>
    </tt><tt>var arr = getInitialData();</tt><tt><br>
    </tt><tt>async.forEach(arr, execute, function (err) {</tt><tt><br>
    </tt><tt>&nbsp; // check for error and/or proceed further</tt><tt><br>
    </tt><tt>});</tt><br>
    <br>
    You could use one of many available control flows, check out <a
      href="https://github.com/caolan/async/blob/master/README.md">many
      more control flows</a>. The advantage is the package provides
    different control flows without having to keep re-inventing them.
    Say, you want to perform certain activity in parallel, or in series,
    or based on some conditionals, while we could write code to achieve
    that, I would recommend using <tt>async</tt> as it is well written
    and <a href="https://npmjs.org/package/async">thoroughly tested</a>
    piece of code.<br>
    <br>
    Where you want to place the execute code depends on many factors,
    like do we need to access/modify other variables in scope, if
    independent operations, they can go in library functions.<br>
    <br>
    Please share your thoughts.<br>
    <br>
    <br>
    <div class="moz-cite-prefix">On 09/13/2012 11:30 AM, Maxim Kazantsev
      wrote:<br>
    </div>
    <blockquote
      cite="mid:a2190a65-fc4c-41a4-a95b-178c9280fafb@googlegroups.com"
      type="cite">It is a pretty typical approach to use an anonymous
      function for asynchronous calls from inside a loop:
      <div><br>
      </div>
      <div>
        <blockquote class="gmail_quote" style="margin: 0px 0px 0px
          0.8ex; border-left-width: 1px; border-left-color: rgb(204,
          204, 204); border-left-style: solid; padding-left: 1ex; ">var
          a = getInitialData();<br>
          for (var i = 0, len = a.length; i &lt; len; i++) {<br>
          &nbsp; (function(el) {<br>
          &nbsp; &nbsp; /* do something non-blocking here */<br>
          &nbsp; })(a[i]);<br>
          }</blockquote>
        <div><br>
        </div>
        <div>JSLint doesn't like this code with "Don't make functions
          within a loop" warning, and it is actually right since it
          really creates a new anonymous function on every single loop
          iteration. An obvious solution is to declare this function
          outside a loop, but it would make a code less readable. Even
          if a declaration would just precede the loop: you see a call
          here, you see a declaration somewhere else, and here you are,
          lost all your attention.</div>
      </div>
      <div><br>
      </div>
      <div>My question is how bad this approach is for an overall
        performance? In particular, how fast and efficient a garbage
        collection of anonymous functions is? How much memory a typical
        anonymous function can consume and how long it may exist in a
        memory?</div>
      -- <br>
      Job Board: <a moz-do-not-send="true"
        href="http://jobs.nodejs.org/">http://jobs.nodejs.org/</a><br>
      Posting guidelines: <a moz-do-not-send="true"
href="https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines">https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines</a><br>
      You received this message because you are subscribed to the Google<br>
      Groups "nodejs" group.<br>
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        href="http://groups.google.com/group/nodejs?hl=en?hl=en">http://groups.google.com/group/nodejs?hl=en?hl=en</a><br>
    </blockquote>
    <br>
    <pre class="moz-signature" cols="72">-- 
Regards,
Vinayak</pre>
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