qtvcp: exit cleanly on SIGTERM/SIGINT#4078
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qtvcp registered self.shutdown as the SIGTERM/SIGINT handler, but two things stopped it working: Qt's C++ event loop (APP.exec()) does not return to Python often enough to run Python signal handlers, and shutdown() cleans up without quitting the loop, so even when reached the process kept running. A caller tearing qtvcp down therefore had to escalate to SIGKILL. Quit the event loop on the signal (APP.quit()) so APP.exec() returns and the existing post-exec shutdown() runs the normal cleanup once, and add a periodic no-op QTimer so the interpreter gets a chance to run the signal handler during exec(). Quitting the loop bypasses the window-close confirmation dialog, which is correct for a terminate request and leaves that interactive feature untouched. Fixes the hang for all qtvcp screens (qtdragon, qtplasmac, ...). Verified qtdragon exits cleanly on SIGTERM and SIGINT. Surfaced by the ui-smoke tests (PR LinuxCNC#4054).
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qtvcp screens (qtdragon etc.) ignored SIGTERM and SIGINT: Python signal handlers do not run while
QApplication.exec()blocks in the Qt C++ loop, so the process never exited and ui-smoke teardown escalated to SIGKILL.This quits the Qt loop directly on SIGTERM and SIGINT, and adds a low-frequency
QTimerso the interpreter periodically regains control to deliver the signal. The existing post-execshutdown()still runs the cleanup. The X-button "are you sure?" confirmation dialog is left intact for interactive close; only the terminate signals bypass it, which is correct for SIGTERM.Part of the SIGTERM clean-shutdown work discussed in #4054.