`getChildPids` ran `pgrep -P <pid>` per node and recursed with no visited set, no
depth limit and no node cap. Two further sites forked a `pgrep` per session on
every stats tick.
Across ~28 adopted tmux trees the fan-out exploded, and because each `pgrep`
blocks in the kernel while reading `/proc/<pid>/cgroup` under WSL, none returned
while the walk kept spawning more. Observed: ~13,000 `pgrep` processes stuck in
D-state out of ~39,000 total, load average above 13,000, and a machine only
recoverable by restarting WSL — which cost every running session. Every diagnostic
command timed out too, because they read /proc as well.
- ONE `ps -eo pid=,ppid=` snapshot, cached briefly and refreshed asynchronously
with a single-flight guard. Async matters: under the same procfs pathology,
`execSync`'s timeout cannot return (spawnSync waits for the unkillable child),
which would freeze the server where a hung async poll only costs staleness.
- The traversal moved to `proc-tree.ts` as a pure function — breadth-first, with a
visited set (a stale snapshot can contain a cycle), a depth cap and a node cap,
both reporting when they truncate. Pure so the regression tests can exercise the
shipped code rather than a copy of it.
- The kill path forces a fresh snapshot: the wait between SIGTERM and the survivor
re-scan (200ms) sits inside the cache TTL (2000ms), so reading the cache there
would return pre-SIGTERM state and aim SIGKILL at stale PIDs. That wait is
bounded, so a wedged `ps` cannot stop killSession from reaching its
process-group and tmux fallbacks.
- Any `ps` error keeps the previous snapshot instead of caching partial output as
fresh; a truncated table would make whole subtrees invisible to the kill path.
13 tests, including one that drives TmuxManager itself — with the caps bypassed at
the call site, 3 of them fail. The snapshot refresh is stubbed there, because
otherwise the manager runs a real `ps`, replaces the fixture, and the test
silently measures the machine's own process tree instead.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claudia
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