1047220 - Shrink the static atoms table

Status: RESOLVED FIXED

(Core :: XPCOM, defect)

Description

[Nicholas Nethercote [inactive]]

The static atoms table has this type:

> nsDataHashtable<nsStringHashKey, nsIAtom*>

Each entry's key is an nsString and its value is a nsIAtom pointer... but those
types store basically the same data. We can remove the nsString and reduce the
size of entries and the whole table as follows (if my calculations are
correct).

* 32-bit: entries: 20 bytes to 8 bytes;  table:  80 KiB to 32 KiB
* 64-bit: entries: 32 bytes to 16 bytes; table: 128 KiB to 64 KiB

Comment 1

[Nicholas Nethercote [inactive]]

Attachment: Shrink the static atoms table

Suggestion on a better way to compare two char16_t strings are welcome.

Comment 2

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 8465980 [details] [diff] [review]
Shrink the static atoms table

>+  typedef char16ptr_t KeyType;

Why not use |const nsAString&| as the KeyType?

>+  typedef char16ptr_t KeyTypePointer;

And |const nsAString*| here.  Basically crib nsStringHashKey.

>+    return nsString(aKey).Equals(nsString(mAtom->GetUTF16String()));

And this would become:

  return mAtom->Equals(aKey);

>+        gStaticAtomTable->PutEntry(atom->GetUTF16String());

  PutEntry(nsDependentAtomString(atom))

>+    gStaticAtomTable->GetEntry(PromiseFlatString(aUTF16String).get());

  GetEntry(aUTF16String)

And then you won't have issues with embedded nulls (not like someone should be doing that with static atoms anyway).

r=me with that.

Comment 3

[Nicholas Nethercote [inactive]]

> Why not use |const nsAString&| as the KeyType?

Mmm, good idea.

A try run (without that change) looks good: https://tbpl.mozilla.org/?tree=Try&rev=67eaeb215af7

Comment 4

[Nicholas Nethercote [inactive]]

Another good-looking try run, this time with bz's suggested change:
https://tbpl.mozilla.org/?tree=Try&rev=cf2ab78eef8c

Comment 5

[Nicholas Nethercote [inactive]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/99a0f93939d2

Comment 6

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/99a0f93939d2