setTimeout without a DOM window using Timer.jsm

[Matt Brubeck]

I noticed a number of places in Mozilla code where setTimeout-like
functionality is needed, but DOM window.setTimeout is not available
because the code runs in a non-DOM context like a JSM. In a few places
we had created pure-JS implementations of window.setTimeout to solve
this problem.

With Gavin's encouragement, I extracted one of these into a standalone
JSM file, to make it easier to share. If you need to call setTimeout
without a DOM window, you can now use Timer.jsm:

https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/Timer.jsm

This offers two main benefits over just using nsITimer directly: it
makes it easier to re-use code written for use in a DOM window, and it
addresses this common nsITimer garbage collection problem:
http://www.joshmatthews.net/blog/2011/03/nsitimer-anti-pattern/

For more details, see bug 840360. Thank you to Chris Jones who wrote
the original code, and to several other people who gave feedback on it.

[Simon Kornblith]

Now might be a good time to try to bring up https://bugzilla.mozilla.org/show_bug.cgi?id=776798
again. Anything called from an nsITimerCallback from a JSM runs
without the method JIT unless you explicitly set
Components.utils.methodjit in the callback or use window.setTimeout on
the hidden DOM window instead. This still happens in the latest
Nightly.

I never heard back whether this was intentional or not, and this may
not matter most of the time since often there's not much code running
in the nsITimerCallback, but in our extension we got a ~30% speedup on
some performance-critical code by setting Components.utils.methodjit
back to whatever it was outside of the callback.

Simon

On Mar 2, 7:47 pm, Matt Brubeck <mbrub...@mozilla.com> wrote:
> I noticed a number of places in Mozilla code where setTimeout-like
> functionality is needed, but DOM window.setTimeout is not available
> because the code runs in a non-DOM context like a JSM.  In a few places
> we had created pure-JS implementations of window.setTimeout to solve
> this problem.
>
> With Gavin's encouragement, I extracted one of these into a standalone
> JSM file, to make it easier to share.  If you need to call setTimeout
> without a DOM window, you can now use Timer.jsm:
>

> https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modu...