[5SP] Investigate high CPU usage in GNU Radio and OpenDigitizer

[ivan-cukic]

CPU usage in the OpenDigitizer UI is too high. The issues likely lie in both the GNU Radio core and UI Needs to be investigated and improved.

Specific Actions:

• replace runAndWait scheduler (busy polling issue)
• implement/use blocking scheduler with UI updates only on progress() changes
• investigate Emscripten's wait implementation vs native
• limit UI's FPS to <25 Hz (with optional 60 Hz global variable)
• profile threading and identify busy polling threads