225274 - synchronous XMLHttpRequest freezes browser, maxes CPU

Status: RESOLVED DUPLICATE of bug 190313

(Core :: XML, defect)

Description

[Geoff Smith]

User-Agent:       Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.5a) Gecko/20031010 Mozilla Firebird/0.6 StumbleUpon/1.88
Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.5a) Gecko/20031010 Mozilla Firebird/0.6 StumbleUpon/1.88

A synchronous xmlhttprequest will hang the browser and max out the cpu until it
has received a response.

The url http://www.stumbleupon.com/test.html sends a xmlhttprequest to a script
called sleep.php that just sleeps for 10 seconds before returning a response. 
You will notice our CPU at 100% for 10 seconds and the browser GUI will not respond.


Reproducible: Always

Steps to Reproduce:
1. go to http://www.stumbleupon.com/test.html
Actual Results:  
CPU at 100% for 10 seconds, browser GUI freezes

Expected Results:  
No gui freeze, minimal CPU usage.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Why are we manually calling ProcessPendingEvents here?  It looks like we should
do something more like what
http://lxr.mozilla.org/seamonkey/source/embedding/components/windowwatcher/src/nsWindowWatcher.cpp#290
does...

Comment 2

[Heikki Toivonen (remove -bugzilla when emailing directly)]

I have tried several different things, but I can't remember if I tried the thing
in nsWindowWatcher. If that works, then DOMParser, document.load and the XSLT
code (or it might now use a generic sync loader, actually) should be fixed to
use that. The biggest problem has been embedding - it's easy to make things not
block in Mozilla proper, but doing it for embedded apps has turned out to be not
so easy.

Anyway, this is dupe, so should continue discussion there...

*** This bug has been marked as a duplicate of 190313 ***