1745443 - Keep alive the MIDIAccess and MIDIPort objects as long as there's pending activity

Status: RESOLVED FIXED

(Core :: DOM: Device Interfaces, task)

Description

[Gabriele Svelto [:gsvelto] (PTO)]

My investigation in how Chrome deals with MIDI objects is down to this:

• MIDIAccess objects are kept alive as long as they have a statechange listener and their parent execution context is alive, even if there are no other JS references to them
• MIDIPort objects are kept alive as long as they have not been closed (that is they are open or they're in a pending state and can be opened via a MIDIConnectionEvent). This means that if there are no other JS references but a event handler/listener is present (statechange for both input and output or midimessage for input) we should still keep them alive.

Additionally we should disable the bfcache for pages using the Web MIDI API and implicitly close the ports when the user navigates away from the page using it.

This is somewhat consistent with APIs dealing with network activity (e.g. WebSocket).

Comment 1

[Gabriele Svelto [:gsvelto] (PTO)]

Attachment: Bug 1745443 - Keep MIDI objects alive as long as there's some pending activity r=smaug

MIDI ports will be kept alive even without direct JS references to it under
the following conditions:

• They've not been explicitly closed (they're open or waiting to be)
• A statechange listener is present
• A midimessage listener is present for input ports only
• They've not been disconnected from their owner, when they are we implicitly
  close them

MIDI access objects will be kept alive even without direct JS references to it
under the following conditions:

• A statechange listener is present
• They've not been disconnected from their owner

Finally whenever a MIDI port is in use we disable the bfcache on the
document.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/b0941225b4ed
Keep MIDI objects alive as long as there's some pending activity r=smaug

Comment 3

[Marian-Vasile Laza]

https://hg.mozilla.org/mozilla-central/rev/b0941225b4ed