1151573 - Remove string interning from JSAPI

Status: NEW

(Core :: JavaScript Engine, defect)

Description

[Steve Fink [:sfink] [:s:]]

jsids may be created from interned strings via INTERNED_STRING_TO_JSID, where
"interned" here means the JSAPI notion, which I believe is what would
ordinarily be called "pinned": they cannot be moved in memory or collected
until unpinned.

The JSAPI exposes

  JS_StringHasBeenInterned
  JS_Intern*String*
  JS_GetLatin1InternedStringChars
  JS_GetTwoByteInternedStringChars

The notion of "interning" (pinning) is dangerous to expose. It makes it easy to create uncollectable garbage. It's even somewhat dangerous, given that we have a notion of unpinning these strings (pinning is not permanent). Unpinning could cause them to be collected unexpectedly or orphaned, if we implement moving GC for strings.

Comment 1

[Boris Zbarsky [:bzbarsky]]

The places where we use this right now in DOM/xpconnect code are:

1)  We preemptively intern a string being used as the value of a property, because shortly after that we use that same string as a property name (which atomizes anyway); this way we don't end up with two copies of the string around.

2)  We intern some strings that we then INTERNED_STRING_TO_JSID and store the jsid for later use.

We don't ever need the chars-getting APIs or JS_StringHasBeenInterned in DOM code.  But we do need a way to produce jsids that we can then have hanging around for later, as things stand: just using strings all the time is too slow because it has to reatomize over and over.