Subj : Re: JavaScript performance in the real world
To   : Pete Diemert
From : Brendan Eich
Date : Fri Sep 17 2004 06:35 pm

Pete Diemert wrote:

> ...fairly typical stuff.  The problem is that opening a recordset object, as
> you might expect, can be costly and code similar to that above will chew up
> literally 10's of megabytes of heap space with recordset objects in a matter
> of seconds.  When a GC finally kicks in everything is cleaned up but we can
> see the working set issue easily becoming a constraint in many real world
> scenarios where we wish to use JavaScript.


Then it's up to your embedding to run the GC more often.  Pending a 
better GC in the engine that scans while allocating (an incremental GC), 
you have to call JS_GC or JS_MaybeGC.

You should certainly use JS_SetBranchCallback to configure a branch 
callback on each JSContext that will increment an unsigned counter 
associated with the context (perhaps kept in its private data, got and 
set via JS_Get/SetContextPrivate), and for every (counter & 0x3fff) or 
so backward branches, call JS_MaybeGC.


> One other interesting note is
> that we have attempted to call GC at periodic moments throughout processing
> on return from native function calls (e.g. every so many seconds) but we
> find that the GC is CONSIDERABLY slower when the scriptdepth is greater than
> 0 (we have scenarios of approximately 5K JS objects allocated where the GC
> will take 30 seconds).  If the scriptdepth is 0 the GC will be nearly
> instaneous (perhaps extra roots are created for objects in frame?).


Possibly, but if so, then you can always try JS_MaybeGC on return to 
outermost level.  That won't hurt much at all if the heap hasn't grown.


> Understanding that JavaScript is a GC / "managed" environment and that,
> architecturally we could be trying to fit a square peg in a round hole, are
> there some techniques that we could use to make this system work better?
> Perhaps just solving the slow GC problem will get us there.  Any suggestions
> or insight would be greatly appreciated.


I hope the above helps.  If not, let me know.

/be

.