On Apr 22, 9:01 am, Danny Tuppeny wrote:
> Here's a small sample page that seems to leak in the same
> way as jQuery:
>
> <html><head><script type="text/javascript">
> function leakMe() {
> var div = document.createElement("div");
> document.body.appendChild(div);
> document.body.removeChild(div);}
>
> </script></head><body onload="leakMe();"></body></html>
>
> The docs for Drip say that removeChild is just a psuedo-leak
> and will be cleaned up when the page is unloaded, but that
> doesn't happen. If you set the above page to Auto-refresh
> in Drip, memory usage just goes up and up forever. If you
> can find a way to stop that happening in the small sample,
> I suspect fixing jQuery will be easy.
There is a problem here but I suspect that problem is with Drip and
not IE or JQuerry (there may be problems with IE and/or JQuery but if
so they are not being demonstrated here).
Starting with the following more extreme example of the - appendChild
-, - removeChild - sequence; appending 100,000 DIVs, stopping with an
- alert - (to give the opportunity for garbage collection to run and
memory use to be examined), removing all of those DIVs from the DOM,
stopping again, and then repeating/looping the process, should, if the
memory leak issue exists (in relation to - removeChild - use) result
in ever increasing memory consumption, which should be noticeable
using crude examination techniques (such as reading the iexplorer
process's "Mem Usage" in Task Manage) due to the number of DIVs
created. However, using this test page:-
<html>
<head>
<title></title>
<style type="text/css">
</style>
</head>
<body>
<script type='text/javascript'>
function createDivs(){
var div;
for(var c = 0;c < 100000;++c){
div = document.createElement('DIV');
document.body.appendChild(div);
}
alert('Divs set');
setTimeout(clearDom, 3000);
}
window.onload = createDivs;
function clearDom(){
while(document.body.lastChild){
document.body.removeChild(document.body.lastChild);
}
alert('Divs cleared');
setTimeout(createDivs, 3000);
}
</script>
</body>
</html>
(The 3 second delay between function calls is to give you time to
close the browser when enough has been seen)
- running in IE 6 (on XP) gives an oscillating (by about 9 megabytes)
"Mem Usage", with no overall accumulation of memory consumption as the
script continues to add and remove DIVs, and running in IE 8 (on XP)
showed the memory use increase with the first addition and then stay
at about that level. What I did not observe at all was any steady
increase in memory use, as would be expected if a memory leak issue
existed here.
This suggests that IE's garbage collection is successfully dealing
with this situation without even getting to the point where re-loading
the page is significant.
On the other hand, running the same code in Drip (with the number of
DIVs created reduced to 10,000 because Drip slows the script down
considerably) showed a steady increase in memory consumption.
Consuming more each time the DIV addition-removal cycle was executed.
This would lead me to conclude that:-
1. The rumours of issues relating to the use of - removeChild - are
unsubstantiated and so should be ignored. If they do relate to a
memory leaking cause and effect relationship then the - removeChild -
use is not (in isolation, or directly) the cause of whatever effect is
being observed.
2. Drip should not be regarded as a definitive indicator of memory
leak issues as it appears to directly provoke some of the issues it
attempts to report.
3. Any supposed memory leak issues with JQuery should be demonstrated
in isolation else time and (script) performance could be squandered
attempting to 'fix' non-issues.
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