1191648 - don't keep ScriptProcessorNodes alive when they have no audioprocess listeners

Status: RESOLVED FIXED

(Core :: Web Audio, defect)

Description

[Karl Tomlinson (:karlt)]

There is no need to keep unreferenced ScriptProcessorNodes to dispatch audioprocess events if there are no listeners.

Comment 1

[Karl Tomlinson (:karlt)]

Attachment: don't keep ScriptProcessorNode alive when it has no audioprocess listener

Comment 2

[Karl Tomlinson (:karlt)]

Attachment: unreferenced script processors in cycles with no event handlers

With this testcase, the initial patch is not sufficient.

Comment 3

[Karl Tomlinson (:karlt)]

Attachment: don't create audioprocess event when there is no listener

Creating the event added a reference to the ScriptProcessorNode, which isn't
released until the AudioProcessingEvent is destroyed in
nsCycleCollector::FreeSnowWhite().

If another event is dispatched before cycle collection considers the
ScriptProcessorNode, then the node will not be collected.

Also, the reference count of the ScriptProcessorNode is no longer toggled
because this seemed to interfere with the cycle collection process.

Without the reference count change, ScriptProcessorNodes from attachment
8645547 were eventually collected in opt builds but not debug builds, so I
suspect timing was involved.  In a debug build, forcing a complete CC from
about:memory would collect the nodes, but this would not happen during regular
CC.  I'm guessing perhaps related to the multi-stage nature of the CC process
needing to restart each time the refcount is toggled.

Comment 4

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/131c6f3f88d1
https://hg.mozilla.org/integration/mozilla-inbound/rev/da775fa17639

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/131c6f3f88d1
https://hg.mozilla.org/mozilla-central/rev/da775fa17639

Comment 6

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/a79804d69e9b

Comment 7

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/a79804d69e9b