1532636 - nsPrefBranch should unregister itself as observer when shutting down

Status: RESOLVED FIXED

(Core :: Preferences: Backend, enhancement)

Description

[Andrea Marchesini [:baku]]

nsPrefBranch unregisters itself as observer in the DTOR:

https://searchfox.org/mozilla-central/rev/92d11a33250a8e368c8ca3e962e15ca67117f765/modules/libpref/Preferences.cpp#2068-2076

But this could be too late in case the nsObserverService has been already in the shutting down phase. Here is why:

1. nsObserverService is released on shutdown because of this:
   https://searchfox.org/mozilla-central/rev/92d11a33250a8e368c8ca3e962e15ca67117f765/xpcom/build/XPCOMInit.cpp#685-688

2. nsPermissionManager is released by ClearOnShutdown, and that happens here:
   https://searchfox.org/mozilla-central/source/xpcom/build/XPCOMInit.cpp#691-695

3. releasing nsPermissionManager we release nsPrefBranch which calls nsObserverService in its dtor. Here is the crash: https://searchfox.org/mozilla-central/rev/92d11a33250a8e368c8ca3e962e15ca67117f765/xpcom/ds/nsObserverService.cpp#177-181

The correct fix is to remove the observer when xpcom-shutdown is notified.
At the same time, nsObserverService should be less aggressive and allow the removeObserver() when mShuttingDown is set to true.

Comment 1

[Andrea Marchesini [:baku]]

Attachment: Bug 1532636 - nsPrefBranch should unregister itself as observer when shutting down, r=gsvelto

Comment 2

[Andrea Marchesini [:baku]]

Attachment: Bug 1532636 - nsObserverService should allow RemoveObserver() to be called when shutting down, r=gsvelto

Depends on D22086

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/35f5d2d519eb
nsPrefBranch should unregister itself as observer when shutting down, r=gsvelto
https://hg.mozilla.org/integration/autoland/rev/8c835f11c111
nsObserverService should allow RemoveObserver() to be called when shutting down, r=gsvelto

Comment 4

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/35f5d2d519eb
https://hg.mozilla.org/mozilla-central/rev/8c835f11c111