GCD and AppleEvents / NSOperationQueue and AppleScript

Question

As i understood, the threads provided by GCD do have a runloop but no source/port. Now i use some of methods that call AppleScripts thru AppleEvents inside an NSOperationQueue. And sometimes my app crashes with following stacktrace.

my questions:

• Usage of AppleScript inside a NSInvocationOperation or NSBlockOperation
• Usage of AppleEvents inside GCD-Threads
• do i have to add a source / port to a runloop of a gcd-thread before using AppleEvents?
• do i have to add a source / port to a runloop of a gcd-thread before using [CATransaction commit]?
• do i have to add a source / port to a runloop of a gcd-thread before using [NSObject performSelectorAfterDelay...] ?
• if yes, how?
• can i simply call CFRunLoopRunInMode(kCFRunLoopDefaultMode, 5.0, false); /// or 30 or the defined timeout of appleevent?

..

Thread 9: Dispatch queue: com.apple.root.default-priority
0 libSystem.B.dylib 0x00007fff88276e82 semaphore_wait_signal_trap 10
1 libSystem.B.dylib 0x00007fff8827c3cd pthread_mutex_lock 469
2 com.apple.applescript 0x000000011d3d461f AppleScriptComponent 50
3 com.apple.applescript 0x000000011d3edbcc AGenericCall::Delegate(ComponentInstanceRecord*) 46
4 com.apple.applescript 0x000000011d3ed520 AGenericManager::HandleOSACall(ComponentParameters*) 54
5 com.apple.applescript 0x000000011d3ed4b0 GenericComponent 219
6 com.apple.openscripting 0x00007fff8381c6da OSAExecuteEvent 63
7 com.apple.Foundation 0x00007fff86f320d8 -[NSAppleScript(NSPrivate) _executeAppleEvent:withMode:error:] 161
8 xxx 0x0000000100048af0 -[TCallScript callScript:withArrayOfParameters:] 480
9 xxx 0x0000000100048ffd -[TCallScript callHandler:withParameters:] 477
10 xxx 0x0000000100036032 -[ZFOpenWindowController getSafariItemForCurrentTabForWindow:] 66
11 xxx 0x00000001000346af -[ZFOpenWindowController refreshWindowList:] 1679
12 xxx 0x000000010003541c -[ZFOpenWindowController bringZFToForegroundZoomOut:orJustLinkFrontMost:toItem:] 2988
13 xxx 0x0000000100053556 __-[ZFSelectionTool openWithPreferredApplication:]_block_invoke_516 54
14 com.apple.Foundation 0x00007fff86ed87d9 -[NSBlockOperation main] 140
15 com.apple.Foundation 0x00007fff86ec906d -[__NSOperationInternal start] 681
16 com.apple.Foundation 0x00007fff86ec8d23 ____startOperations_block_invoke_2 99
17 libSystem.B.dylib 0x00007fff882b2ce8 _dispatch_call_block_and_release 15
18 libSystem.B.dylib 0x00007fff88291279 _dispatch_worker_thread2 231
19 libSystem.B.dylib 0x00007fff88290bb8 _pthread_wqthread 353
20 libSystem.B.dylib 0x00007fff88290a55 start_wqthread 13


...


Thread 11 Crashed: Dispatch queue: com.apple.root.default-priority
0 com.apple.applescript 0x000000011d40f658 BCHandleError() 182
1 com.apple.applescript 0x000000011d4059ca UASExecute1() 2546
2 com.apple.applescript 0x000000011d3dd1d5 ASExecuteEvent(AEDesc const*, unsigned int, int, unsigned int*) 695
3 ...ple.CoreServices.CarbonCore    0x00007fff85388e04 CallComponentFunction 28
4 com.apple.applescript 0x000000011d3d4cad AppleScriptComponent 1728
5 com.apple.applescript 0x000000011d3edbcc AGenericCall::Delegate(ComponentInstanceRecord*) 46
6 com.apple.applescript 0x000000011d3ed520 AGenericManager::HandleOSACall(ComponentParameters*) 54
7 com.apple.applescript 0x000000011d3ed4b0 GenericComponent 219
8 com.apple.openscripting 0x00007fff8381c6da OSAExecuteEvent 63
9 com.apple.Foundation 0x00007fff86f320d8 -[NSAppleScript(NSPrivate) _executeAppleEvent:withMode:error:] 161
10 xxx 0x0000000100048af0 -[TCallScript callScript:withArrayOfParameters:] 480
11 xxx 0x0000000100048ffd -[TCallScript callHandler:withParameters:] 477
12 xxx 0x0000000100035c67 -[ZFOpenWindowController getItemForAXDocumentOfFrontMostWindow] 119
13 xxx 0x00000001000359f1 -[ZFOpenWindowController getItemForFrontMostWindow:] 721
14 xxx 0x00000001000348ac -[ZFOpenWindowController bringZFToForegroundZoomOut:orJustLinkFrontMost:toItem:] 60
15 xxx 0x0000000100053556 __-[ZFSelectionTool openWithPreferredApplication:]_block_invoke_516 54
16 com.apple.Foundation 0x00007fff86ed87d9 -[NSBlockOperation main] 140
17 com.apple.Foundation 0x00007fff86ec906d -[__NSOperationInternal start] 681
18 com.apple.Foundation 0x00007fff86ec8d23 ____startOperations_block_invoke_2 99
19 libSystem.B.dylib 0x00007fff882b2ce8 _dispatch_call_block_and_release 15
20 libSystem.B.dylib 0x00007fff88291279 _dispatch_worker_thread2 231
21 libSystem.B.dylib 0x00007fff88290bb8 _pthread_wqthread 353
22 libSystem.B.dylib 0x00007fff88290a55 start_wqthread 13

Answer 1

Note that the AppleScript component has limited thread safety. As of 10.6, you can use it on non-main threads, but you will need to create a new ComponentInstance for each thread. I think you can do this with OSAKit, otherwise you'll need to resort to the gnarly Carbon API. What's best really depends on what you're trying to achieve (e.g. are you running user-supplied scripts, or scripts hardcoded into your application, and what's the motivation for running them via NSOperationQueue).