1442760 - Switch nsHTMLTags hashtables to nsDataHashtable

Status: RESOLVED FIXED

(Core :: DOM: HTML Parser, enhancement)

Description

[Eric Rahm [:erahm]]

We should really avoid using PL_Hash if possible. Converting `gTagTable` and `gTagAtomTable`[1] is pretty straightforward.

[1] https://searchfox.org/mozilla-central/rev/908e3662388a96673a0fc00b84c47f832a5bea7c/parser/htmlparser/nsHTMLTags.h#83-84

Comment 1

[Eric Rahm [:erahm]]

Attachment: Switch nsHTMLTags hashtables to nsDataHashtable

This converts nsHTMLTags hashtables from PLHash to nsDataHashtable which
gives us both type safety and simpler code. Addtionally `gTagTable` now holds
a nsString instead of a raw char16_t pointer, this has the benefit of the
strings knowing their sizes allowing for more efficient comparisons. We avoid
heap allocations in the nsString by using `AssignLiteral` with the string from
the static string array.

Comment 2

[Henri Sivonen (:hsivonen)]

Comment on attachment 8956677 [details] [diff] [review]
Switch nsHTMLTags hashtables to nsDataHashtable

Review of attachment 8956677 [details] [diff] [review]:
-----------------------------------------------------------------

::: parser/htmlparser/nsHTMLTags.cpp
@@ +92,5 @@
>    if (gTableRefCount++ == 0) {
>      NS_ASSERTION(!gTagTable && !gTagAtomTable, "pre existing hash!");
>  
> +    gTagTable = new TagStringHash(64);
> +    gTagAtomTable = new TagAtomHash(64);

Is there a reason to use 64 instead of a number derived from the number of tags?

Comment 3

[Eric Rahm [:erahm]]

(In reply to Henri Sivonen (:hsivonen) from comment #2)
> Comment on attachment 8956677 [details] [diff] [review]
> Switch nsHTMLTags hashtables to nsDataHashtable
> 
> Review of attachment 8956677 [details] [diff] [review]:
> -----------------------------------------------------------------
> 
> ::: parser/htmlparser/nsHTMLTags.cpp
> @@ +92,5 @@
> >    if (gTableRefCount++ == 0) {
> >      NS_ASSERTION(!gTagTable && !gTagAtomTable, "pre existing hash!");
> >  
> > +    gTagTable = new TagStringHash(64);
> > +    gTagAtomTable = new TagAtomHash(64);
> 
> Is there a reason to use 64 instead of a number derived from the number of
> tags?

It's just what we used before, I don't know why it was chosen. For a hashtable we'll want a number a bit larger than the number of entries to avoid collisions so that might be what's going on here.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/8bbb6c0d3214
Switch nsHTMLTags hashtables to nsDataHashtable. r=hsivonen

Comment 5

[Cristian Brindusan [:cbrindusan]]

https://hg.mozilla.org/mozilla-central/rev/8bbb6c0d3214