188006 - PAC: pauses while loading pages (complicated script #2)

Status: RESOLVED WORKSFORME

(Core :: Networking, defect)

Description

[Jacob Vogelstein]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.2.1) Gecko/20021130
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.2.1) Gecko/20021130

After months of irritation and frustration trying to decipher the source of this
bug -- http://bugzilla.mozilla.org/show_bug.cgi?id=155181 -- I stumbled upon the
reason why only I noticed this problem.  I have always had an automatic proxy
configuration script located at some remote url, and EVERY TIME I LOAD A PAGE,
the browser hangs for a few seconds.  For some pages, it hangs multiple times
and recovers multiple times.  Sometimes the hang is 500 msec and sometimes it's
5 sec.  Anyway, by some stroke of luck I happened to forget to configure my
proxy server when I downloaded the newest build and now it works fine.  

So the problem is:
With a remote automatic proxy configuration script, the browser is completely
unresponsive every time a new page element is loaded from a different remote
source.  So the website listed above is a good example because it has multiple
different advertising graphics, each loaded from a different server.  I think
what is happening is there is an initial freeze when the page is loaded as the
browser tries to check with the remote proxy script to see whether the page
should be proxied, then each time it comes across an element from a new source,
it repeats the process.  Since I can see my proxy script, I know that the pages
I'm looking at do not actually get proxied by the remote server, but I bet
Mozilla is checking every time anyway.

Suggested solution:
The browser should load the proxy configuration once at startup, then cache the
information.  When a page element comes from a non-proxied server, it should not
access the remote proxy URL. Alternately, it should at least do screen writes
while it waits for a response from the proxy host.  

Reproducible: Always

Steps to Reproduce:
1. Go to Preferences->Advanced->Proxies and select "Automatic Proxy
Configuration URL"
2. I use http://proxy.hosts.jhmi.edu/proxy.pac
3. Open any webpage

Actual Results:  
Browser hangs for a few moments until (presumably) it hears from the proxy
server that the page I'm viewing should not be proxied

Expected Results:  
Cache the proxy configuration script and for non-proxied pages, bypass the
remote proxy host.

Comment 1

[benc]

-> PAC.

Comment 2

[Ray Charbonneau]

This, bug #180811, and bug #100022 all appear to be dupes or related to bug
#83984.  Since #100022 has the most votes, I'll add my vote there in the hopes
that it will do some good.  This bug will force my corporation to go to IE if
it's not fixed soon!

Comment 3

[benc]

Attachment: captured pac file

Comment 4

[benc]

I don't think this is the same problem discussed in the previous comment, I've
attached the PAC file, and it loads a huge array and does shell expression for
every domain in the array.

I think what happens here is general javascript badness.

Comment 5

[Jacob Vogelstein]

It may be poorly written JavaScript, but Mozilla should cache the file upon
startup (after expansion or whatever) and then not access the proxy server
unless the user navigates to an address specified in the PAC file.  I don't know
how the other browsers work, but IE and Opera seem to handle it fine...

Comment 6

[Boris Zbarsky [:bzbarsky]]

Jacob, are you sure we hit the proxy server?  Looking over the PAC code we _do_
cache the PAC file....

I suspect that Ben is right and the issue is that FindProxyForURL() is called
for each URL that may need proxying.  And that implementation of FindProxyForURL
is very slow.... As a test, try moving the declaration of ncl out of the
function?  I suspect that that will greatly reduce the hangs you see.

Comment 7

[kmike]

I was hit by this bug after installing similar banner zapper:
http://www.schooner.com/~loverso/no-ads/
Mozilla slows to crawl (basically hangs) on every URL click, and then every 10
secs during page load.

Comment 8

[Trevor Nuridin]

Some observations of mine -

1) Mozilla 1.5 on windows doesn't suffer from this anywhere near as bad as
mozilla 1.5 on linux does, in the same office environment (ie. same proxy server
etc etc). Mozilla on linux is very tedious for me to use, but I use mozilla on
winxp without too many hassles, even though they both use the same .pac file.
Typing in a manual proxy setup on the linux version 'fixes' the problem, so
looks like something about the .pac stuff it doesn't cope with.

2) Konquerer using the same .pac setup on the same linux box works well.
3) I installed firebird 0.6 to cross check with it, and it doesn't seem to
suffer from this problem on the same linux box either - so this problem looks
peculiar to mozilla only.

Comment 9

[Boris Zbarsky [:bzbarsky]]

Trevor, the PAC code in Firebird and Mozilla should be absolutely identical.  Is
this a problem with a clean profile?  It sounds like you have some preference
setting that leads to this behavior.... (and hence not seeing this bug, which is
not dependent on any particular preferences).

Comment 10

[Trevor Nuridin]

yes, whoops, sorry. My lack of testing. Firebird does the same thing as mozilla.
I installed firebird and tested it for about 15 minutes of surfing, which
normally the problem occurs heaps of times, but murphy came along and hid the
problem. I just spent another 15 minutes surfing in firebird and the problem
arose just like in mozilla.

So diregard my comment about firebird.

Comment 11

[Darin Fisher]

can this problem be reproduced with a recent trunk build?

trevor: can you please download a nightly build of mozilla and report back on
how it performs under linux?  thx!

Comment 12

[Trevor Nuridin]

Yes - I installed the nightly build 2003102705 onto the box and it exhibits the
same symptoms.
I'm a little strapped for time for the next couple of days, but I will do some
more detailed testing soon.

Comment 13

[Darin Fisher]

trevor: when you do get time, could you please provide a HTTP log via:

  http://www.mozilla.org/projects/netlib/http/http-debugging.html

thx!

Comment 14

[Wayne Mery (:wsmwk)]

Darin in comment #13
> trevor: when you do get time, could you please provide a HTTP log via:
> 
>   http://www.mozilla.org/projects/netlib/http/http-debugging.html
> 
> thx!

Darin, Trevor appears to be gone, and reporter too.