FYI: This is the actual script sample that 3.6.9.-1 cannot handle properly:
.........
if [[ $case == all || ( -a "$tmp/$daemon$i.lst" && -s
"$tmp/$daemon$i.lst" ) ]]; then
if [[ "$1" == -test ]]; then
[[ -n $ra || -n $bc ]] && Wait
{
time nmake -a -nologo -k -f $mutil/$daemon$i.mak \
makefile=$daemon$i update=no case=$case
msdebug=$msdebug dir=. nrt=$nrt $dllver
} >_test$i.log 2>&1 &
found=yes
elif [[ "$1" == -update ]]; then
[[ -n $ra || -n $bc ]] && Wait
{
time nmake -a -nologo -k -f $mutil/$daemon$i.mak \
update=yes case=$case dir=$dir makefile=$daemon$i
msdebug=$msdebug nrt=$nrt $dllver
} >_test$i.log 2>&1 &
found=yes
fi
else
rm -f $TMP/$daemon$i.lst
fi
i=$((1+$i))
done
if [[ $found == no && $difs == yes ]]; then
echo "$DAEMON: $(date "$format"): ERROR: Error in makefiles. No
tests found."
return 203
elif [[ $difs == no ]]; then
echo "$DAEMON: $(date "$format"): WARNING: No tests found to
update."
return 0
fi
wait
.........
Where Wait() is a throttling function that allows to run concurrently a given
number (like 15 in this case) of 'nmake' processes, and the low case 'wait' is
the bash wait.
Nick
> -----Original Message-----
> From: Takashi Yano <[email protected]>
> Sent: Monday, August 24, 2026 6:41 AM
> To: [email protected]
> Cc: Nick Popoff <[email protected]>
> Subject: Re: Regression in Cygwin 3.6.9: Deadlock when spawning many
> concurrent Windows-native processes (nmake.exe) — works in 3.6.5 1
>
> Thanks for the report.
>
> I guess the patch:
> https://cygwin.com/pipermail/cygwin-patches/2026q3/015286.html
> fixes the issue. Please wait for test version of cygwin, where the patch
> applied. The patch is now under review, so hopefully it will become soon.
>
> On Mon, 24 Aug 2026 06:22:06 -0400
> Nick Popoff via Cygwin <[email protected]> wrote:
>
> > Hello,
> >
> >
> >
> > Regression in Cygwin 3.6.9: Deadlock when spawning many concurrent
> > Windows-native processes (nmake.exe) — works in 3.6.5‑1
> >
> > Version affected: Cygwin 3.6.9 (latest as of August 2026)
> >
> > Version NOT affected: Cygwin 3.6.5‑1 (stable, no issues)
> >
> >
> >
> > Summary
> >
> > Cygwin 3.6.9 introduces a regression in process management that causes
> complete build deadlock when spawning many concurrent Windows-native
> processes (specifically nmake.exe). The same workload has run flawlessly for
> 20+ years on all previous Cygwin versions, including 3.6.5‑1. Under 3.6.9, the
> build freezes once some parallel job limit is reached, leaving dozens of idle
> sh.exe processes and stalled nmake.exe processes. Ctrl‑C kills the Windows
> nmake.exe processes but Cygwin’s sh.exe instances remain stuck, and the
> terminal never returns control. Reverting to 3.6.5‑1 immediately restores
> correct behavior. This is a reproducible regression in Cygwin’s
> process/signal/pipe handling.
> >
> >
> >
> > Environment
> >
> > * Windows Server 2025 (WS2025)
> > * Heavy parallel build workload
> > * 15 concurrent nmake.exe processes
> > * Each nmake.exe spawns many short-lived Windows-native tools
> > * Cygwin shell (sh.exe) orchestrates the build
> > * No Cygwin-native processes involved — all Windows-native
> >
> >
> >
> > Steps to Reproduce
> >
> > 1. Install Cygwin 3.6.9
> > 2. Launch a Cygwin shell
> > 3. Start 15 parallel Windows-native builds, e.g.:
> >
> > Code
> >
> > for i in {1..15}; do
> >
> > (nmake.exe -f Makefile$i &)
> >
> > done
> >
> > wait
> >
> > Each makefile repeatedly spawns short-lived Windows-native tools (ASN.1-
> compiler processes).
> >
> > 4. Observe behavior once all 15 jobs are active.
> >
> >
> >
> > Actual Behavior (3.6.9)
> >
> > * Build freezes completely once a certain parallel limit is reached
> > * All nmake.exe processes become idle
> > * Dozens of idle sh.exe accumulate
> > * No CPU usage
> > * No progress
> > * Ctrl‑C kills nmake.exe but does not kill sh.exe
> > * Cygwin console never returns
> > * Terminal must be forcibly closed
> > * No such behavior in 3.6.5‑1
> >
> > This is consistent with a signal-thread or pipe inheritance deadlock.
> >
> >
> >
> > Expected Behavior (3.6.5‑1 and earlier)
> >
> > * All 15 parallel nmake.exe processes run normally
> > * No idle sh.exe accumulation
> > * No deadlock
> > * Ctrl‑C cleanly terminates all processes
> > * Console returns immediately
> > * Build completes successfully
> >
> > This behavior has been stable for decades.
> >
> >
> >
> > Notes
> >
> > This workload is a strong stress test for:
> >
> > * spawn.cc
> > * sigproc.cc
> > * pipe inheritance
> > * process table updates
> > * console control handling
> > * synchronization primitives
> >
> > The regression appears only in 3.6.9.
> >
> >
> >
> > Conclusion
> >
> > Cygwin 3.6.9 introduces a reproducible deadlock when orchestrating many
> concurrent Windows-native processes via Cygwin’s shell. This is a regression
> from 3.6.5‑1. The issue affects real-world build systems and should be
> investigated.
> >
> > I can provide:
> >
> > * process snapshots
> > * strace logs
> > * Windows process tree dumps
> > * minimal reproduction scripts
> >
> > upon request.
> >
> >
> >
> > Nick
> >
> >
> >
> >
> >
> >
> >
> >
> > --
> > Problem reports: https://cygwin.com/problems.html
> > FAQ: https://cygwin.com/faq/
> > Documentation: https://cygwin.com/docs.html
> > Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
>
>
> --
> Takashi Yano <[email protected]>
--
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