This patch changes JS array resizing to prefer power-of-two sized slot
requests. Previously it would mostly make slightly-more-than-power-of-two sized
requests that cause lots of slop.
Also, shrinkElements() now only does a reallocation if it would result in going
down a size class. E.g. if you pop all the elements from a 1000-element array,
it would realloc 999, then 998, then 997, all the way down the minimum size.
Now it does 512, then 256, down to the minimum size (which is 8).
I confirmed with DMD that the element allocations now have zero slop. This
reduces peak RSS loading a couple of large PDF files (four times each) with
pdf.js by 10s of MiBs.
This patch changes JS array resizing to always allocate power-of-two sized slot
requests. Previously it would mostly make slight-more-than-power-of-two sized
requests, which cause lots of slop.
Also, shrinkElements() now only does a reallocation if it would result in going
down a size class. E.g. if you pop all the elements from a 1000-element array,
it would realloc 999, then 998, then 997, all the way down the minimum size.
Now it does 512, then 256, down to the minimum size (which is 8).
I confirmed with DMD that the element allocations now have zero slop. This
reduces peak RSS loading a couple of large PDF files (four times each) with
pdf.js by 10s of MiBs.
This thing is basically only useful for ye olde JS_InitClass classes where
people might try to create objects with external JSClasses and expect various
defaults when they invoke JS_NewObject. Let's move it out of the way.
Object.keys, Object.getOwnPropertyNames, and for-in loops skip symbol-keyed
properties per spec, but Object.defineProperties sees them, and a future
Reflect.ownKeys API will need to be able to see them.
This patch changes the comments on JSITER_FOREACH and JSITER_KEYVALUE, but not
the behavior. The comments were just wrong.
This is unnecessary now that object jsids no longer exist. Both string and
symbol jsids point only to GC things in the atoms compartment, which are safe
to pass to any compartment without wrapping.
This exposes a new primitive type to scripts for the first time since
JavaScript first shipped in Netscape 2, over 13 years ago.
The tests focus on identity, equality, and being able to pass a symbol around
as a value. Of course the point of symbols is that they can be property keys,
but that will have to wait for a later patch in this series.
