1
我們有一個覆蓋drawSelectionInRect的NSTableRowView的子類：（它由drawRect內部調用:)。這個方法需要訪問NSManagedObjectContext，所以作爲一個完整的檢查，我們有一個斷言，我們在主線程中。現在事實證明，有時Apple會從非主線程調用drawRect（下面的示例堆棧跟蹤）。這是否意味着它甚至可以從兩個不同的線程同時進行？即在覆蓋drawRect時，我們必須自己考慮線程安全：並使用數據模型？Mac OS是否調用drawRect等顯示方法：來自不同線程的併發？訪問數據模型時沒有那麼危險嗎？
ERROR: Assertion failed: [NSThread isMainThread]: (ZS_AppDelegate.m:1287)
(
0 tomedo_kunden 0x00000001008af46a -[ZS_AppDelegate loggedInUser] + 554
1 tomedo_kunden 0x00000001016feca7 +[Nutzer loggedInUser] + 71
2 tomedo_kunden 0x0000000100f33397 +[ZSUserDefaults(MacOS) colorFromPreferences:] + 167
3 tomedo_kunden 0x00000001003d8265 -[Besuch(BesuchCategory) baseTextColor] + 101
4 tomedo_kunden 0x000000010071f846 -[ZSTableRowView drawSelectionInRect:] + 806
5 AppKit 0x00007fffd189d26c -[NSTableRowView drawRect:] + 242
6 AppKit 0x00007fffd184eba3 -[NSView(NSInternal) _recursive:displayRectIgnoringOpacity:inGraphicsContext:CGContext:topView:shouldChangeFontReferenceColor:] + 1318
7 AppKit 0x00007fffd184f053 -[NSView(NSInternal) _recursive:displayRectIgnoringOpacity:inGraphicsContext:CGContext:topView:shouldChangeFontReferenceColor:] + 2518
8 AppKit 0x00007fffd184e548 __46-[NSView(NSLayerKitGlue) drawLayer:inContext:]_block_invoke + 267
9 AppKit 0x00007fffd184e071 -[NSView(NSLayerKitGlue) _drawViewBackingLayer:inContext:drawingHandler:] + 1589
10 AppKit 0x00007fffd184da36 -[NSView(NSLayerKitGlue) drawLayer:inContext:] + 80
11 AppKit 0x00007fffd19839ff -[_NSBackingLayerContents drawLayer:inContext:] + 162
12 QuartzCore 0x00007fffd96a1e42 -[CALayer drawInContext:] + 257
13 AppKit 0x00007fffd19834d8 -[_NSTiledLayer drawTile:inContext:] + 624
14 AppKit 0x00007fffd198320e -[_NSTiledLayerContents drawLayer:inContext:] + 176
15 QuartzCore 0x00007fffd96a1e42 -[CALayer drawInContext:] + 257
16 AppKit 0x00007fffd1983155 -[NSTileLayer drawInContext:] + 169
17 QuartzCore 0x00007fffd9584a38 CABackingStoreUpdate_ + 3740
18 QuartzCore 0x00007fffd96a1a3c ___ZN2CA5Layer8display_Ev_block_invoke + 75
19 QuartzCore 0x00007fffd96a169d _ZN2CA5Layer8display_Ev + 1803
20 AppKit 0x00007fffd198306c -[NSTileLayer display] + 119
21 QuartzCore 0x00007fffd9695546 _ZN2CA5Layer17display_if_neededEPNS_11TransactionE + 572
22 QuartzCore 0x00007fffd9695671 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 35
23 QuartzCore 0x00007fffd968ae88 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 280
24 QuartzCore 0x00007fffd9581d55 _ZN2CA11Transaction6commitEv + 475
25 AppKit 0x00007fffd19701d9 __58-[_NSScrollingConcurrentVBLMonitor _updateScrollAnimation]_block_invoke + 972
26 AppKit 0x00007fffd196aa3a -[_NSScrollingConcurrentSharedData threadSafePropertyAccess:] + 44
27 AppKit 0x00007fffd196d127 -[_NSScrollingConcurrentVBLMonitor _updateScrollAnimation] + 672
28 AppKit 0x00007fffd196c84e -[_NSScrollingConcurrentVBLMonitor _synchronizeForVBLSerialNumber:timestamp:updateDuration:] + 561
29 AppKit 0x00007fffd196c5ad __42-[_NSScrollingConcurrentVBLMonitor resume]_block_invoke + 218
30 AppKit 0x00007fffd196c4ca __45-[NSScreen(NSScreenUpdate) addUpdateHandler:]_block_invoke_2 + 212
31 libdispatch.dylib 0x000000010345ffcc _dispatch_client_callout + 8
32 libdispatch.dylib 0x0000000103476bca _dispatch_continuation_pop + 1025
33 libdispatch.dylib 0x000000010346c6bc _dispatch_source_latch_and_call + 195
34 libdispatch.dylib 0x0000000103462e15 _dispatch_source_invoke + 1106
35 libdispatch.dylib 0x00000001034768f0 _dispatch_continuation_pop + 295
36 libdispatch.dylib 0x000000010346deda _dispatch_async_redirect_invoke + 777
37 libdispatch.dylib 0x0000000103462247 _dispatch_root_queue_drain + 671
38 libdispatch.dylib 0x0000000103461f58 _dispatch_worker_thread3 + 114
39 libsystem_pthread.dylib 0x00000001034d78c2 _pthread_wqthread + 1299
40 libsystem_pthread.dylib 0x00000001034d739d start_wqthread + 13
)
如果你直接從drawRect中訪問CoreData，你應該修改你的架構。 –