1295101 - ctypes.jsm uses a lot of memory due to resolving lazy properties on the global

Status: RESOLVED FIXED

(Core :: js-ctypes, defect)

Description

[Jan de Mooij [:jandem]]

ctypes.cpp has the following code:

  // Finally, seal the global object, for good measure. (But not recursively;
  // this breaks things.)
  return JS_FreezeObject(cx, global);

This ends up resolving lazy properties on the global. Due to all the DOM prototype objects, this is relatively slow and uses a lot of memory.

Removing this line wins about 180 KB per content process (242,864 -> 64,832 bytes)

Before:

│  │   │  ├────242,864 B (00.54%) -- compartment([System Principal], resource://gre/modules/ctypes.jsm)
│  │   │  │    ├──198,160 B (00.44%) -- classes
│  │   │  │    │  ├───88,800 B (00.20%) ++ shapes
│  │   │  │    │  ├───74,144 B (00.17%) ++ class(Function)/objects
│  │   │  │    │  └───35,216 B (00.08%) ++ class(<non-notable classes>)/objects
│  │   │  │    ├───32,896 B (00.07%) ── compartment-tables
│  │   │  │    └───11,808 B (00.03%) -- sundries
│  │   │  │        ├──10,848 B (00.02%) ── malloc-heap
│  │   │  │        └─────960 B (00.00%) ── gc-heap

After:

│  │   │  ├─────64,832 B (00.15%) -- compartment([System Principal], resource://gre/modules/ctypes.jsm)
│  │   │  │     ├──48,400 B (00.11%) -- classes
│  │   │  │     │  ├──29,264 B (00.07%) ++ class(<non-notable classes>)/objects
│  │   │  │     │  └──19,136 B (00.04%) ++ shapes
│  │   │  │     └──16,432 B (00.04%) ++ sundries

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Patch

This "seal the global" code was added 7 years ago (bug 513788). It might be less useful now since CPG and it's likely not worth the 180 KB memory per process.

Comment 2

[Nicholas Nethercote [inactive]]

Nice.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/c70cf61a5f1d
Don't freeze the ctypes.jsm global to avoid resolving all properties on it. r=bholley

Comment 4

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/c70cf61a5f1d