tools/ustat: Properly handle SIGINT in ustat

[jeromemarchand]

Most interactive tools waiting for a keyboard interrupt just expect it during sleep() call. In most case it works well enough since most of the time is typically spend in sleep. In the case of tclstat however, the tool can spend a lot of time detaching uprobes, in self.bpf.cleanup() more specifically and it fails when CTRL+C is pressed.

Fix this by catching the SIGINT signal. We still want to raise KeyboardInterrupt while sleeping though, for the tool to exit immediately when possible.

Fixes the following error:
10:12:42 loadavg: 0.03 0.05 0.01 2/289 21928

PID CMDLINE METHOD/s GC/s OBJNEW/s CLOAD/s EXC/s THR/s
21926 tclsh ./fib.tcl 2 2 0 8 0 0 0
^Cioctl(PERF_EVENT_IOC_DISABLE) failed: Bad file descriptor
close perf event FD failed: Bad file descriptor
Exception ignored in atexit callback: <bound method BPF.cleanup of <bcc.BPF object at 0x7f00481bbc20>>
Traceback (most recent call last):
File "/usr/lib/python3.12/site-packages/bcc/init.py", line 1855, in cleanup
self.detach_uprobe_event(k)
File "/usr/lib/python3.12/site-packages/bcc/init.py", line 1507, in detach_uprobe_event
raise Exception("Failed to detach BPF from uprobe")
Exception: Failed to detach BPF from uprobe

[Copilot]

Pull request overview

This PR updates the ustat tool loop to handle SIGINT more safely, aiming to avoid failures when Ctrl-C happens during lengthy probe cleanup (notably with Tcl uprobes).

Changes:

• Add a custom SIGINT handler to control when KeyboardInterrupt is raised.
• Track whether the tool is currently sleeping to preserve “exit immediately” behavior during sleep().
• Install the SIGINT handler during run().

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

_sigint_handler reads self.in_sleep, but in_sleep is only set inside _loop_iter. If SIGINT arrives before the first iteration (or between iterations), this will raise AttributeError from inside the signal handler. Initialize self.in_sleep = False before installing the handler (e.g., in run()), or use getattr(self, 'in_sleep', False) in the handler.

[Copilot]

If sleep() is interrupted, execution jumps to the except KeyboardInterrupt block and self.in_sleep stays True. That can cause later SIGINTs (e.g., during detach/cleanup) to incorrectly raise KeyboardInterrupt, reintroducing the cleanup failure this PR is trying to avoid. Ensure self.in_sleep is always reset (e.g., move it into a finally block).

Suggested change

	self.in_sleep = False
	except KeyboardInterrupt:
	self.exiting = True
	except KeyboardInterrupt:
	self.exiting = True
	finally:
	self.in_sleep = False

[Copilot]

With the custom SIGINT handler, SIGINT received outside the sleep() window (e.g., during _attach_probes() or printing) sets self.exiting = True but _loop_iter() will still call sleep(self.args.interval) on that iteration. Consider checking self.exiting before sleeping so Ctrl-C exits promptly when possible (while still allowing cleanup to run).

[Copilot]

self.exiting = True; ends with a semicolon, which triggers pycodestyle E703 (and scripts/py-style-check.sh runs pycodestyle over tools/**/*.py). Remove the trailing semicolon to avoid CI/style check failures.

Suggested change

	self.exiting = True;
	self.exiting = True