subprocess.run(capture_output=True, timeout=N) is not hang-safe on
Windows: after the timeout fires, run()'s cleanup kills the direct child
and then joins the pipe reader threads with an UNBOUNDED communicate().
A descendant (conhost.exe under wmic/powershell) holding duplicated pipe
handles keeps the pipes from EOF and the join never returns.
_scan_gateway_pids() runs its wmic / Get-CimInstance Win32_Process scans
exactly that way, and on machines where the full process scan genuinely
exceeds its 10/15s budget (cold WMI on first boot, ARM VMs, heavy
Update/AV activity) hermes update wedged forever inside
_pause_windows_gateways_for_update() before printing a single line —
observed live on a fresh Windows 11 ARM64 VM with a faulthandler stack
pinning the main thread in subprocess._communicate and only a conhost.exe
child surviving. The single-flight update lock then blocks retries until
the wedged process is killed by hand.
This is the same deadlock class bounded_git_probe already fixed for git
probes (#68609 / #66037). Generalize that proven pattern into a shared
bounded_probe_run() — explicit communicate(timeout), kill_process_tree on
failure, bounded 1s drain, then abandon the daemonic readers — and
migrate the whole call-site class onto it:
- hermes_cli/gateway.py _scan_gateway_pids (the site that hung; reached
from hermes update, cron, gateway restart/status, dashboard)
- hermes_cli/dashboard_procs.py wmic scan (same shape, reached on update)
- hermes_cli/claw.py tasklist + PowerShell probes (same shape; its
try/except cannot catch a hang because a hang raises nothing)
- bounded_git_probe now delegates to bounded_probe_run (identical
contract, one copy of the cleanup logic)
Unlike bounded_git_probe, bounded_probe_run returns the CompletedProcess
(or None) rather than collapsing to stdout, because the gateway scan
branches on returncode to trip its wmic -> powershell fallback.
Tests: tests/hermes_cli/test_bounded_probe_run.py covers success,
nonzero-exit passthrough, spawn failure, bounded timeout (fails against
the old unbounded semantics — verified by sabotage), errors= decoding,
DEVNULL stdin, POSIX process-group placement, and the bounded_git_probe
delegation contract. Existing test_git_probe_tree_kill.py passes
unchanged against the delegated implementation.
Closes#87134
kshitij
4e3de140c1