Why std::this_thread::sleep_for() is broken on ESP32

A curious bug appearing after upgrading to IDF v5 led me into a deep dive of how std::this_thread::sleep_for() is implemented on the ESP32. I discuss how the IDF implements pthreads and newlib to provide C++ threading functionality. The results are surprising: a simple 10 millisecond sleep was killing performance, but only in the new version of IDF due to an interaction between libstdc++ and usleep() .