NSArrayController backed array modification in background thread - multithreading

Question

Here is the situation:
NSTableView bound to a NSArrayController
NSArrayController bound to an array of AnalysisResult objects
dynamic var analysisResults: [AnalysisResult] = [AnalysisResult]() // model for table view via resultsArrayController
The NSTableView has a column "result" bound to AnalysisResult.value
Now when the user clicks on a button, it triggers an analysis in a background thread, and modifies the objects in "analysisResults". It does NOT add nor remove any object from the array. It just changes the "value" property of the AnalysisResult objects.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
for (index, curAnalysisRes) in self.analysisResults.enumerate() {
curAnalysisRes.value = "some new value" // simplified but the value can be updated in many different places of the algorithm
}
dispatch_sync(dispatch_get_main_queue()) {
/* Ask the tableview to reload data in main UI thread */
self.myTableView.reloadData()
}
}
After the analysis, the UI thread is asked to update the table view.
BUT here is the problem: I get the following warning:
CoreAnimation: warning, deleted thread with uncommitted CATransaction; created by:
0 QuartzCore 0x00007fff8f06369a _ZN2CA11Transaction4pushEv + 318
1 QuartzCore 0x00007fff8f06319a _ZN2CA11Transaction15ensure_implicitEv + 276
2 QuartzCore 0x00007fff8f069719 _ZN2CA5Layer13thread_flags_EPNS_11TransactionE + 37
3 QuartzCore 0x00007fff8f069668 _ZN2CA5Layer4markEPNS_11TransactionEjj + 64
4 QuartzCore 0x00007fff8f06b12b _ZN2CA5Layer25set_needs_display_in_rectERK6CGRect + 333
5 QuartzCore 0x00007fff8f06afdc -[CALayer setNeedsDisplayInRect:] + 25
6 AppKit 0x00007fff872d12e8 _NSBackingLayerSetNeedsDisplayInRect + 319
7 AppKit 0x00007fff872d11a3 -[_NSBackingLayer setNeedsDisplayInRect:] + 61
8 QuartzCore 0x00007fff8f06af9d -[CALayer setNeedsDisplay] + 62
9 AppKit 0x00007fff872d198b -[NSView(NSInternal) _setLayerNeedsDisplayInViewRect:] + 606
10 AppKit 0x00007fff8729f88e NSViewSetNeedsDisplayInRect + 945
11 AppKit 0x00007fff8729f4d6 -[NSView setNeedsDisplayInRect:] + 48
12 AppKit 0x00007fff8729f2ed -[NSView setNeedsDisplay:] + 81
13 AppKit 0x00007fff872f2be1 -[NSTextFieldCell setObjectValue:] + 88
14 AppKit 0x00007fff873e3026 -[NSControl setObjectValue:] + 135
15 AppKit 0x00007fff873ce0c6 -[_NSPlaceholderTextFieldPlugin showValue:inObject:] + 110
The warning is caused by modifying the array bound to the arraycontroller.
I do not want to perform the analysis in the main thread because it freezes the UI.
How can I avoid the warning?

Answer 1

OK I have found the solution here, and it was pretty straightforward.
Since I was modifying the values of the array bound to the NSArrayController and since the controller is bound to a NSTableView (thus UI-related), I was obviously doing UI-stuff not in the main UI thread.
Technically speaking, since cocoa bindings use KVO (key-value observing), the change notifications triggered by my modifications in the array, were propagated in a non-UI thread, causing the up-mentionned message:
CoreAnimation: warning, deleted thread with uncommitted CATransaction;
Furthermore, an interesting side-effect, the piece of code:
self.myTableView.reloadData()
is not necessary anymore because the KVO notifications now propagate properly in the UI-thread.