I used to work on a debugger. It was called TotalView, and it was a really stellar multiprocess, multithread debugger. You could debug programs with thousands of cores and threads. You could type real C++ code to inspect values, inject code into a running process, force the CPU to run at a given line, like a magic goto. But we had a saying "printf wins again". Sometimes you just can't get the debugger to tell you what you need.