Viewing Threads in the Debug Area
Examine your programs threads and stacks inside of Xcode.
Run your application, the debug area opens by default.
Pause your application’s execution, or wait for your code to stop at a breakpoint.
Choose a thread from the pop-up menu in the debug bar.
Examine the corresponding source or assembly code.
The debug area lets you examine the threads and stacks of a program being debugged. When you select a thread or a stack within a thread in the debug bar, Xcode displays the corresponding source file or assembly code in the main editor.
The screenshot shows the debug area while choosing a thread and a stack frame to examine.