Collection was mutated while being enumerated crash with NSTableView, NSArrayController and NSThread

Question

Hi!

In my small Core Data application I have some NSTableView views binded with NSArrayController controllers in Entity mode.

When I try to import some big amount of data to my table in background thread, after some successfully added imports (from dozens to hundreds items) I get crash with log:

Serious application error. Exception was caught during Core Data change processing: *** Collection was mutated while being enumerated.NSHashTable (%@) { [5] (entity: Word; id: 0x1001dd4b0 ; data: { ....... entity description here.... } ....

...and stack trace:

#0  0x7fff83e0e2fa in mach_msg_trap
#1  0x7fff83e0e96d in mach_msg
#2  0x7fff8816c614 in _CGSSynchronizeWindowBackingStore
#3  0x7fff88152169 in _CGSLockWindow
#4  0x7fff88158cff in CGSDeviceLock
#5  0x7fff81ecae43 in ripd_Lock
#6  0x7fff81eca746 in ripl_BltShape
#7  0x7fff81ec7d86 in ripc_Render
#8  0x7fff81ec5317 in ripc_DrawRects
#9  0x7fff88158641 in CGContextFillRects
#10 0x7fff8818ee1a in CGContextFillRect
#11 0x7fff86e712f8 in NSRectFillUsingOperation
#12 0x7fff86f2152e in NSDrawWindowBackground
#13 0x7fff86ea16c2 in -[NSThemeFrame drawWindowBackgroundRect:]
#14 0x7fff86e6eb9a in -[NSFrameView drawThemeContentFill:inView:]
#15 0x7fff86e68aa5 in -[NSThemeFrame drawRect:]
#16 0x7fff86e68131 in -[NSView _drawRect:clip:]
#17 0x7fff86e65907 in -[NSView _recursiveDisplayRectIfNeededIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:topView:]
#18 0x7fff86e64ee8 in -[NSThemeFrame _recursiveDisplayRectIfNeededIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:topView:]
#19 0x7fff86e6179a in -[NSView _displayRectIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:]
#20 0x7fff86ddaff6 in -[NSView displayIfNeeded]
#21 0x7fff86dd5ea2 in _handleWindowNeedsDisplay
#22 0x7fff80099a2d in __NSFireTimer
#23 0x7fff815aa678 in __CFRunLoopRun
#24 0x7fff815a884f in CFRunLoopRunSpecific
#25 0x7fff82c3991a in RunCurrentEventLoopInMode
#26 0x7fff82c3971f in ReceiveNextEventCommon
#27 0x7fff82c395d8 in BlockUntilNextEventMatchingListInMode
#28 0x7fff86dab29e in _DPSNextEvent
#29 0x7fff86daabed in -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:]
#30 0x7fff86d708d3 in -[NSApplication run]
#31 0x7fff86d695f8 in NSApplicationMain

Assuming there is an issue with updating table (enumeration not being thread safe), I have tried to solve this problem by disabling controller and table before import starts using:

[wordsController setEditable:NO];
[wordsController setAutomaticallyPreparesContent:NO];
[wordsTable setEnabled:NO];

but it does not help. During import I still see new entities being added to the tale until crash.

Anyone knows what is the trick to disable NSArrayController from tracking changes for a time of background processing? Or maybe it is other issue here?

Thank You very much for any hints.

Answer 1

Are you using fast enumeration ( "for (id object in collection) {...}" ) in your import or UI update? If so, note that you can't modify the collection (add or remove) during enumeration.

It's also possible this is the result of inserting into the same context your array controller is refreshing from. In which case, you'd need a separate "import" context from your "display results" context. During import, you'll merge the contexts every x imported objects, allowing the "display results" context to refresh.