Here it is. I don't understand much. The only information I can add is that thread 4 do not systematically appear. Besides that, the backtraces are consistent.
Thread 4 (process 37173):
#0 0x00007fff826119da in __workq_kernreturn ()
#1 0x00007fff82611dec in _pthread_wqthread ()
#2 0x00007fff82611a55 in start_wqthread ()
Thread 3 (process 37173):
#0 0x00007fff826119da in __workq_kernreturn ()
#1 0x00007fff82611dec in _pthread_wqthread ()
#2 0x00007fff82611a55 in start_wqthread ()
Thread 2 (process 37173):
#0 0x00007fff82610bba in kevent ()
#1 0x00007fff82612a85 in _dispatch_mgr_invoke ()
#2 0x00007fff8261275c in _dispatch_queue_invoke ()
#3 0x00007fff82612286 in _dispatch_worker_thread2 ()
#4 0x00007fff82611bb8 in _pthread_wqthread ()
#5 0x00007fff82611a55 in start_wqthread ()
Thread 1 (process 37173):
#0 0x00007fff87e7011c in objc_msgSend ()
#1 0x00007fff802332b0 in -[NSCarbonMenuImpl _carbonMenuInsertItem:atCarbonIndex:] ()
#2 0x00007fff80393f5b in -[NSCarbonMenuImpl _privatePopulateCarbonMenu] ()
#3 0x00007fff80393d77 in -[NSCarbonMenuImpl _carbonPopulateEvent:handlerCallRef:] ()
#4 0x00007fff80393b60 in NSSLMMenuEventHandler ()
#5 0x00007fff86032bd7 in DispatchEventToHandlers ()
#6 0x00007fff86032126 in SendEventToEventTargetInternal ()
#7 0x00007fff86031f97 in SendEventToEventTargetWithOptions ()
#8 0x00007fff86073e2d in SendMenuPopulate ()
#9 0x00007fff86073c6e in PopulateMenu ()
#10 0x00007fff860732fe in Check1MenuForKeyEvent ()
#11 0x00007fff86072a08 in CheckMenusForKeyEvent ()
#12 0x00007fff86072644 in _IsMenuKeyEvent ()
#13 0x00007fff8607236a in IsMenuKeyEvent ()
#14 0x00007fff80393914 in -[NSCarbonMenuImpl _menuItemWithKeyEquivalentMatchingEventRef:] ()
#15 0x00007fff803936cb in _NSFindMenuItemMatchingCommandKeyEvent ()
#16 0x00007fff80264c35 in _NSHandleCarbonMenuEvent ()
#17 0x00007fff802386a2 in _DPSNextEvent ()
#18 0x00007fff80237b41 in -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] ()
#19 0x00007fff801fd747 in -[NSApplication run] ()
#20 0x00007fff801f6468 in NSApplicationMain ()
#21 0x0000000101d09770 in ?? ()
#22 0x0000000101d00314 in ?? ()
#23 0x0000000100040ff9 in ruby_run_node ()
#24 0x0000000100179769 in macruby_main ()
#25 0x0000000100000e70 in main ()