`Stack overflow` occurs when co_await asynchronous function in the loop

[shelllet]

The application crash occurs when co_await asynchronous function in the loop.

      co_await resume_background();

        for (int i = 0; i < 10000; ++i) {

            co_await Test();
       }

1. download source code
   https://github.com/shelllet/winui_stack_overflow.git

2. compile and run

3. click button 'clickme'

error:

Symbol loading disabled by Include/Exclude setting.
Exception thrown at 0x00007FF7BAD5A77F in App1.exe: 0xC00000FD: Stack overflow (parameters: 0x0000000000000001, 0x0000007CC4403F88).
Unhandled exception at 0x00007FF7BAD5A77F in App1.exe: 0xC00000FD: Stack overflow (parameters: 0x0000000000000001, 0x0000007CC4403F88).

2021-05-23.15-25-01.mp4

[jaigak]

Can you show what the test method does?

[shelllet]

Can you show what the test method does?

https://www.github.com/shelllet/winui_stack_overflow/tree/master/App1%2FMainWindow.xaml.cpp

[ranjeshj]

@jevansaks any ideas?

[jevansaks]

A stack would help. But I'm guessing since your Test function completes immediately, the co_await is calling the completion function synchronously, which then calls the next iteration of the loop synchronously, and so forth.

Raymond Chen has a multi-part series on better understanding coroutines in C++: https://devblogs.microsoft.com/oldnewthing/20191209-00/?p=103195

Not a WinUI bug. And probably by design from the C++ compiler's perspective. C++ coroutines have a lot of rough edges.