1527181 - Add flush/resolve microtask heuristic

Status: RESOLVED FIXED

(Core :: Graphics: CanvasWebGL, enhancement, P3)

Description

[Kelsey Gilbert [:jgilbert]]

https://searchfox.org/mozilla-central/source/xpcom/base/CycleCollectedJSContext.h#191

Comment 1

[Kelsey Gilbert [:jgilbert]]

<jgilbert> Jeff Gilbert (jdashg) heycam: Hi! Is there a way to enqueue a Runnable (micro-task??) to run after the current JS Task?
<heycam> jgilbert: I'm sure there is but I'm not really familiar with microtask stuff
<jgilbert> Jeff Gilbert (jdashg) heycam: can you route me if someone else would know more?
<heycam> (there's a type called MicroTaskRunnable I see)
jgilbert: git log tells me mrbkap and asuth
they've written / reviewed a microtask related patch
or smaug probably
<smaug> yes, use MicroTaskRunnable. (and what is a JS Task?)
(I guess it is just a task :) )
<jgilbert> Jeff Gilbert (jdashg) smaug: I'm really guessing at nouns here, haha!
Basically after set of JS calls, if one of them was a webgl call, I'd like to run code as we're returning to the event loop
<smaug> microtask runs at the end of outermost script execution, or at the end of the task.
jgilbert: ahaa, you don't want microtask ,but end-of-task?
<jgilbert> Jeff Gilbert (jdashg) it sounds like microtask would be fine
<mattwoodrow> jgilbert: https://searchfox.org/mozilla-central/source/dom/canvas/CanvasRenderingContext2D.cpp#1446
<jgilbert> Jeff Gilbert (jdashg) like "soon sometime after the current task"
<smaug> there can be several microtasks within a task
end-of-task model is different
our current StableState is basically end-of-task model
<jgilbert> Jeff Gilbert (jdashg) Is StableState "right after the Task is done"? Not "when done with queued tasks"?
<smaug> yes, it is after-the-task-is-done
in Gecko (but not anymore in the spec)
<jgilbert> Jeff Gilbert (jdashg) Is there a more spec-forward-compatible approach I should use?
<smaug> (in the spec stable state is one microtask basically)
jgilbert: are you implementing something from a spec?
<jgilbert> Jeff Gilbert (jdashg) No, but I would like it to keep working and not drift :)
If StableState is stable, that works
I just don't want weird bugs in a year
<smaug> but then hard to say what is correct. StableState is probably fine for now.
→ m_kato joined ([e-mail])
<smaug> jgilbert: we don't let JS to run during StableState, or at least try to assert that
<jgilbert> Jeff Gilbert (jdashg) Specifically, if I call RunInStableState() in a RAF, it'll (probably) run before the next Present?
<smaug> Preset?
Present?
<jgilbert> Jeff Gilbert (jdashg) Present as in "presented to the compositor"
it's some DOM atomicity thing
<smaug> so, if you call RunInStableState during some rAF callback, the stablestate is handled after painting
<jgilbert> Jeff Gilbert (jdashg) I want to run a task between RAF and painting
<smaug> since the task is roughly [rAF callback, flush styling and layout, paint, end-of-task ]
ok, so you don't want end-of-task then :)
<jgilbert> Jeff Gilbert (jdashg) s/run a task/run a runnable/
ok
<smaug> sounds like microtask then
<jgilbert> Jeff Gilbert (jdashg) alright, thanks!
<smaug> there is a microtask checkpoint after each rAF callback
so, if there is such callback, microtask checkpoint is before style flush

Comment 2

[Kelsey Gilbert [:jgilbert]]

So microtask after RAF doesn't help because the task directly after RAF is Paint. However, a heuristic for non-RAF (like requestPostAnimationFrame) would help. Really the best way to handle this would be an eager commit() call, though.

Comment 3

[Kelsey Gilbert [:jgilbert]]

Attachment: Bug 1527181 - Add webgl.auto-flush:true.

• webgl.auto-flush (default: true) enqueues a runnable to flush pending
  webgl commands after each draw.
• webgl.auto-flush.gl (default: false) causes this auto-flush to also
  call glFlush.

This is probably not useful for pure RAF-based apps, since they run
RAF();Present(); back-to-back. For other cases though, this should
improve latency and may reduce jank.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/03f2371bb998
Add webgl.auto-flush:true. r=lsalzman

Comment 5

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/03f2371bb998