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[windows] try to fix hanging processes #134

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Merged
ckreibich merged 2 commits into from
Mar 19, 2026
Merged

[windows] try to fix hanging processes #134

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[windows] try to fix hanging processes
Mar 17, 2026
9b89036
code review changes
Mar 18, 2026
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18 changes: 15 additions & 3 deletions btest-bg-run-helper
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Original file line number Diff line number Diff line change
Expand Up @@ -11,9 +11,15 @@ esac
# taskkill /T terminates the process and all its descendants.
# MSYS_NO_PATHCONV prevents MSYS from interpreting /F, /T, /PID as paths.
win_kill_tree() {
local wpid
if [ $is_windows -eq 1 ] && [ -f .winpid ]; then
wpid=$(cat .winpid)
if [ $is_windows -eq 1 ]; then
local wpid=""
# Prefer the live /proc lookup: after exec the Windows PID may
# differ from the value captured at startup in .winpid.
if [ -n "$pid" ] && [ -f /proc/"$pid"/winpid ]; then
wpid=$(cat /proc/"$pid"/winpid)
elif [ -f .winpid ]; then
wpid=$(cat .winpid)
fi
if [ -n "$wpid" ]; then
MSYS_NO_PATHCONV=1 taskkill /F /T /PID "$wpid" &>/dev/null
fi
Expand Down Expand Up @@ -63,8 +69,14 @@ echo $$ >.pid

# Record the child's Windows PID so that btest-bg-wait can
# reliably terminate it even if MSYS PIDs become stale.
# Also record the child's MSYS PID (.winchildpid): btest-bg-wait
# can use it to look up the *current* Windows PID via /proc at kill
# time, which is more reliable than .winpid because exec may change
# the Windows PID.
# Guard: /proc entry disappears if the child exits before we get here.
if [ $is_windows -eq 1 ] && [ -f /proc/$pid/winpid ]; then
cat /proc/$pid/winpid >.winpid
echo $pid >.winchildpid
fi

wait $pid
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17 changes: 17 additions & 0 deletions btest-bg-wait
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Expand Up @@ -81,6 +81,23 @@ function kill_procs {
MSYS_NO_PATHCONV=1 taskkill /F /T /PID "$wpid" &>/dev/null
fi
fi

# The .winpid captured at startup may hold a stale
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@ckreibich ckreibich Mar 18, 2026

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Is this a "may or may not" for unknown reasons (or perhaps a race condition), or does the /proc/$cpid/winpid case always hold true for Cygwin but not elsewhere and so this is a actually a Cygwin-specific check?

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@mamaorha mamaorha Mar 18, 2026

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On Unix, exec() replaces the process image but preserves the PID — that's a fundamental guarantee. Cygwin/MSYS2 can't do that because Windows has no native exec().
Instead, the runtime spawns a new Windows process and terminates the old one. So after exec():

  • MSYS/Cygwin PID → stays the same (virtual, tracked by the runtime)
  • Windows PID → changes (it's a brand-new native process)

This is exactly why the live /proc/$pid/winpid lookup is needed — .winpid captured the pre-exec Windows PID, which is now dead

# pre-exec Windows PID. Look up the *current* Windows
# PID from /proc using the child's MSYS PID, which
# remains valid and tracks the native process after exec.
if [ -f "$p/.winchildpid" ]; then
local cpid
cpid=$(cat "$p/.winchildpid")
if [ -n "$cpid" ] && [ -f /proc/"$cpid"/winpid ]; then
local live_wpid
live_wpid=$(cat /proc/"$cpid"/winpid)
if [ -n "$live_wpid" ]; then
MSYS_NO_PATHCONV=1 taskkill /F /T /PID "$live_wpid" &>/dev/null
fi
fi
fi

if [ -f "$p/.pid" ]; then
msys_pids="$msys_pids $(cat "$p/.pid")"
fi
Expand Down
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