Fix action_suspend_process deadlock in signal handler #6333
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Root cause: action_suspend_process sent SIGTSTP, whose handler called suspend_application_mode() which does _key_thread.join(). This blocks waiting for the input thread, but the input thread may be posting messages via asyncio which needs the event loop - but the event loop can't run while blocked in the signal handler. This causes a deadlock. Fix: - action_suspend_process now calls suspend_application_mode() directly in normal context, then sends SIGSTOP (not SIGTSTP) - SIGTSTP handler (for external kill -TSTP) schedules the action via call_soon_threadsafe to run in event loop context - _resume_signal now calls refresh(layout=True) to redraw after resume Fixes Textualize#6298
pasky
commented
Jan 17, 2026
| # With that out of the way, send the SIGTSTP signal. | ||
| os.kill(os.getpid(), signal.SIGTSTP) | ||
| self._driver.suspend_application_mode() | ||
| self._driver._must_signal_resume = True |
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N.B. this feels like a layering violation, but I wanted a minimal patch and the whole WINDOWS test cuts through the abstraction anyway.
Perhaps .suspend_application_mode() should just take an argument whether to suspend the process and all of action_suspend_process() would be moved to driver-specific code?
Author
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(Note that I decided to ultimately switch from textual to urwid for my project since I couldn't figure out how to avoid textual's input lag [w/o setting insane FPS], so I'm unlikely to make any followups on this PR - hopefully it still serves as a good base for a fix!) |
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Root cause: action_suspend_process sent SIGTSTP, whose handler called suspend_application_mode() which does _key_thread.join(). This blocks waiting for the input thread, but the input thread may be posting messages via asyncio which needs the event loop - but the event loop can't run while blocked in the signal handler. This causes a deadlock.
Fix:
Fixes #6298