Comments on: Overhauling the XMLHttpRequest documentation

By: Vladimir Dzhuvinov

Vladimir Dzhuvinov — Wed, 29 Oct 2008 06:02:05 +0000

Leaks as in “memory leaks”? :-?

I searched bugzilla for “xmlhttprequest + memory + leak” and couldn’t find any applicable confirmed bugs.

If we put aside good programming practice for a moment, are there really bad things lurking in synchronous XHR?

By: sheppy

sheppy — Fri, 24 Oct 2008 18:47:55 +0000

Vladimir Dzhuvinov –

Firefox 3 no longer blocks the UI when handling synchronous XMLHttpRequests, because otherwise there’s no way for the user to terminate one that’s locked up. It’s strongly recommended that you avoid using synchronous requests, because they can leak in various ways, and asynchronous just isn’t that much more complicted.

By: Vladimir Dzhuvinov

Vladimir Dzhuvinov — Fri, 24 Oct 2008 07:10:40 +0000

Sheppy, thank you for the clarification :)

Today I was trying to find out why the FF3 UI doesn’t freeze on blocking XHR calls (as with earlier versions). I’m developing a standalone xulrunner app and it seems that now the main argument for using asynchronous XHR calls – preventing UI lock-up – is gone. Has synchronous XHR become “safe” now?

Strangely, I couldn’t find any info on this programming issue! It’s important to me because it gives me an option to simplify programming throughout the whole application.

By: sheppy

sheppy — Fri, 17 Oct 2008 14:41:54 +0000

Vladimir: The callback handler runs on the GUI thread; otherwise you wouldn’t have access to the DOM.

By: sheppy

sheppy — Fri, 17 Oct 2008 14:41:26 +0000

Yes, these are 16 bit characters, which is why the high byte gets stripped off to create bytes.

By: boemer

boemer — Fri, 17 Oct 2008 13:57:18 +0000

seems we’re talking about 16bits chars… (utf8?)

By: boemer

boemer — Fri, 17 Oct 2008 13:50:40 +0000

I would remove the high-order bit instead of the byte, I guess, you don’t have much left if you remove the whole byte of a character…

SendAsBinary: The request body as a DOM string. This data is converted to a string of single-byte characters by truncation (removing the high-order !!!byte!!! of each character).

By: Vladimir Dzhuvinov

Vladimir Dzhuvinov — Fri, 17 Oct 2008 06:30:50 +0000

Great, great, great! The new version is a lot clearer!

I’ve got a question though: the callback handler – does it run on the spawned thread or on the GUI thread?

By: Ted Mielczarek

Ted Mielczarek — Fri, 17 Oct 2008 02:43:50 +0000

Looks good! I wrote the original page on kb.mozillazine.org a while back, and copied it to MDC at some point. It wasn’t great, but it was better than nothing. Now it’s well-organized and useful!

By: fabian

fabian — Fri, 17 Oct 2008 00:26:31 +0000

ah nice. thanks.

I hated it not having a good documentation about the XHR implementation in Mozilla. Also multipart! great! <3