793738 - ValueObserver not threadsafe

Status: RESOLVED WONTFIX

(Core :: Preferences: Backend, defect)

Description

[David Zbarsky (:dzbarsky)]

Assertion failure: _mOwningThread.GetThread() == PR_GetCurrentThread() (ValueObserver not thread-safe), at /Users/dzbarsky/mozilla/inbound/modules/libpref/src/Preferences.cpp:131
[1]    95190 segmentation fault  ~/mozilla/obj-inbound/dist/NightlyDebug.app/Contents/MacOS/firefox -P

Comment 1

[David Zbarsky (:dzbarsky)]

Attachment: Patch

Roc, you reviewed the last changes to this file, but feel free to pass this off to someone else if you want.

Comment 2

[Josh Matthews [:jdm]]

I don't think marking it threadsafe is the right solution. The pref service should _never_ be used off the main thread, and this suggests to me that someone is registering/unregistering off the main thread, which is bad.

Comment 3

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Correct. The stack for the assertion should pinpoint the real problem.

Comment 4

[David Zbarsky (:dzbarsky)]

(gdb) bt
#0  mozilla::ValueObserver::Release (this=0x11863aef0) at /Users/dzbarsky/mozilla/inbound/modules/libpref/src/Preferences.cpp:131
#1  0x0000000101015b5b in nsCOMPtr<nsIObserver>::~nsCOMPtr (this=0x118662b88) at nsCOMPtr.h:492
#2  0x0000000101014c25 in nsCOMPtr<nsIObserver>::~nsCOMPtr (this=0x118662b88) at nsCOMPtr.h:489
#3  0x00000001012ea13e in PrefCallback::~PrefCallback (this=0x118662b60) at nsPrefBranch.h:87
#4  0x00000001012e87d5 in PrefCallback::~PrefCallback (this=0x118662b60) at nsPrefBranch.h:85
#5  0x00000001012e940d in nsAutoPtr<PrefCallback>::~nsAutoPtr (this=0x10a93e538) at nsAutoPtr.h:71
#6  0x00000001012e8965 in nsAutoPtr<PrefCallback>::~nsAutoPtr (this=0x10a93e538) at nsAutoPtr.h:70
#7  0x00000001012ea0e5 in nsBaseHashtableET<PrefCallback, nsAutoPtr<PrefCallback> >::~nsBaseHashtableET (this=0x10a93e500) at nsBaseHashtable.h:385
#8  0x00000001012ea0b5 in nsBaseHashtableET<PrefCallback, nsAutoPtr<PrefCallback> >::~nsBaseHashtableET (this=0x10a93e500) at nsBaseHashtable.h:385
#9  0x00000001012e9dac in nsTHashtable<nsBaseHashtableET<PrefCallback, nsAutoPtr<PrefCallback> > >::s_ClearEntry (table=0x10a61e180, entry=0x10a93e500) at nsTHashtable.h:464
#10 0x00000001032a3c4d in PL_DHashTableRawRemove (table=0x10a61e180, entry=0x10a93e500) at pldhash.cpp:684
#11 0x00000001032a3def in PL_DHashTableEnumerate (table=0x10a61e180, etor=0x1012e90e0 <nsBaseHashtable<PrefCallback, nsAutoPtr<PrefCallback>, PrefCallback*>::s_EnumStub(PLDHashTable*, PLDHashEntryHdr*, unsigned int, void*)>, arg=0x7fff5fbfe618) at pldhash.cpp:718
#12 0x00000001012e8b9c in nsBaseHashtable<PrefCallback, nsAutoPtr<PrefCallback>, PrefCallback*>::Enumerate (this=0x10a61e180, enumFunc=0x1012e7410 <FreeObserverFunc(PrefCallback*, nsAutoPtr<PrefCallback>&, void*)>, userArg=0x0) at nsBaseHashtable.h:221
#13 0x00000001012e3e7a in nsPrefBranch::freeObserverList (this=0x10a61e130) at /Users/dzbarsky/mozilla/inbound/modules/libpref/src/nsPrefBranch.cpp:660
#14 0x00000001012e733a in nsPrefBranch::Observe (this=0x10a61e130, aSubject=0x10a606b58, aTopic=0x1046204d4 "xpcom-shutdown", someData=0x0) at /Users/dzbarsky/mozilla/inbound/modules/libpref/src/nsPrefBranch.cpp:607
#15 0x00000001012e738f in non-virtual thunk to nsPrefBranch::Observe(nsISupports*, char const*, unsigned short const*) () at /Users/dzbarsky/mozilla/inbound/modules/libpref/src/nsPrefBranch.cpp:609
#16 0x00000001032d0e06 in nsObserverList::NotifyObservers (this=0x1009fb740, aSubject=0x10a606b58, aTopic=0x1046204d4 "xpcom-shutdown", someData=0x0) at /Users/dzbarsky/mozilla/inbound/xpcom/ds/nsObserverList.cpp:99
#17 0x00000001032d31d7 in nsObserverService::NotifyObservers (this=0x10a61c940, aSubject=0x10a606b58, aTopic=0x1046204d4 "xpcom-shutdown", someData=0x0) at /Users/dzbarsky/mozilla/inbound/xpcom/ds/nsObserverService.cpp:149
#18 0x00000001032af368 in mozilla::ShutdownXPCOM (servMgr=0x10a606b58) at /Users/dzbarsky/mozilla/inbound/xpcom/build/nsXPComInit.cpp:545
#19 0x00000001032af165 in NS_ShutdownXPCOM_P (servMgr=0x10a606b58) at /Users/dzbarsky/mozilla/inbound/xpcom/build/nsXPComInit.cpp:506
#20 0x000000010100a12f in ScopedXPCOMStartup::~ScopedXPCOMStartup (this=0x10a101de0) at /Users/dzbarsky/mozilla/inbound/toolkit/xre/nsAppRunner.cpp:1111
#21 0x000000010100a055 in ScopedXPCOMStartup::~ScopedXPCOMStartup (this=0x10a101de0) at /Users/dzbarsky/mozilla/inbound/toolkit/xre/nsAppRunner.cpp:1093
#22 0x0000000101011b11 in XREMain::XRE_main (this=0x7fff5fbfea78, argc=3, argv=0x7fff5fbff660, aAppData=0x1000081c0) at /Users/dzbarsky/mozilla/inbound/toolkit/xre/nsAppRunner.cpp:3869
#23 0x0000000101011e8f in XRE_main (argc=3, argv=0x7fff5fbff660, aAppData=0x1000081c0, aFlags=0) at /Users/dzbarsky/mozilla/inbound/toolkit/xre/nsAppRunner.cpp:3923
#24 0x0000000100001ebc in do_main (argc=3, argv=0x7fff5fbff660) at /Users/dzbarsky/mozilla/inbound/browser/app/nsBrowserApp.cpp:174
#25 0x0000000100001785 in main (argc=3, argv=0x7fff5fbff660) at /Users/dzbarsky/mozilla/inbound/browser/app/nsBrowserApp.cpp:279

Comment 5

[Josh Matthews [:jdm]]

That doesn't help, unfortunately. Throw an NS_IsMainThread assertion in Prefrences::RegisterCallback and that will tell us where the problem is.

Comment 7

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Comment on attachment 664093 [details] [diff] [review]
Patch

Review of attachment 664093 [details] [diff] [review]:
-----------------------------------------------------------------

Not the right fix.

Comment 8

[BugBot [:suhaib / :marco/ :calixte]]

The bug assignee didn't login in Bugzilla in the last 7 months.
:KrisWright, could you have a look please?
For more information, please visit auto_nag documentation.

Comment 9

[Kris Wright :KrisWright]

ValueObserver in this state was removed.