[CI] Add semaphore isolation helper to avoid hangs

Fix possible stale semaphores during parallel runs
 - isolate semaphores per test run
 - steal semaphore after timeout

Issue:
Semaphores including hostnames, which in turn include uppercase
letters, are not reaped correctly. This lead to hangs of CI runs.

Very recent parallel versions 20260522 and newer handle this case
by converting hostname to lowercase:
https://cgit.git.savannah.gnu.org/cgit/parallel.git/tree/src/parallel?h=20260522#n7565

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: mhalk

bin/semaphore_isolation.src

@@ -0,0 +1,29 @@
+# shellcheck shell=bash
+#
+# semaphore_isolation.src - shared helper for GNU parallel's "sem" semaphore.
+#
+# Source this file and call isolate_semaphore before any "sem" use. It gives
+# "sem" a private, self-cleaning semaphore namespace (its own PARALLEL_HOME) so
+# that a leaked/stale token can neither deadlock a run nor leak across runs, and
+# optionally bounds a stuck semaphore with a timeout.
+#
+# Background: on hosts whose name contains uppercase letters, GNU parallel's
+# dead-lock reaper (remove_dead_locks) never matches its own token files, so a
+# token left behind by an unclean death is never reclaimed and every later
+# "sem --wait" deadlocks. A per-run private namespace sidesteps this entirely.
+#
+# Design:
+#   - No-op when PARALLEL_HOME is already set, so an outer caller never collides.
+#   - AOMP_SEMAPHORE_TIMEOUT (seconds), if set, is passed to every "sem" call as
+#     --semaphoretimeout: a wedged sem/sem --wait then steals and proceeds
+#     instead of hanging. Left unset => pure isolation, no timeout.
+
+isolate_semaphore() {
+  [ -n "${PARALLEL_HOME:-}" ] && return 0
+  _semaphore_home=$(mktemp -d "${TMPDIR:-/tmp}/aomp-sem.XXXXXX") || return 0
+  export PARALLEL_HOME="$_semaphore_home"
+  if [ -n "${AOMP_SEMAPHORE_TIMEOUT:-}" ]; then
+    export PARALLEL="--semaphoretimeout ${AOMP_SEMAPHORE_TIMEOUT}${PARALLEL:+ $PARALLEL}"
+  fi
+  trap 'rm -rf "$_semaphore_home"' EXIT
+}

test/smoke/check_smoke.sh

@@ -227,6 +227,9 @@ if [ "$AOMP_PARALLEL_SMOKE" == 1 ]; then
   fi
   sem --help > /dev/null
   if [ $? -eq 0 ]; then
+    # Give "sem" a private, self-cleaning semaphore namespace (no-op if the
+    # caller already set PARALLEL_HOME). Prevents stale-token deadlocks/leaks.
+    source "${path}/../../bin/semaphore_isolation.src" 2>/dev/null && isolate_semaphore
     COMP_THREADS=1
     MAX_THREADS=16
     if [ ! -z `which "getconf"` ]; then