tools: one Gradle lock helper (gradle-lock.sh) for gradle-serial.sh and clean-builds.sh

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

tools/clean-builds.sh

@@ -5,6 +5,8 @@
 # Prints what it removes and the space freed. Waits for the Gradle lock of tools/gradle-serial.sh, so it never deletes
 # under a running build. The orchestrator runs it after removing a worktree or when the disk is low.
 # Usage from any checkout:  tools/clean-builds.sh [--dry-run]
+# shellcheck source-path=SCRIPTDIR source=gradle-lock.sh
+. "$(dirname "$0")/gradle-lock.sh"
 dry=0
 case "$1" in
   --dry-run) dry=1 ;;
@@ -39,14 +41,8 @@ done > "$list"
 if [ ! -s "$list" ]; then echo "Nothing to remove."; exit 0; fi
 
 if [ "$dry" -eq 0 ]; then
-  lock=/tmp/kvitt-gradle.lock
-  while ! mkdir "$lock" 2>/dev/null; do
-    pid=$(cat "$lock/pid" 2>/dev/null)
-    if [ -n "$pid" ] && ! kill -0 "$pid" 2>/dev/null; then rm -rf "$lock"; continue; fi
-    sleep 5
-  done
-  echo $$ > "$lock/pid"
-  trap 'rm -rf "$lock"; rm -f "$list"' EXIT INT TERM HUP
+  gradle_lock_acquire
+  trap 'rm -rf "$KVITT_GRADLE_LOCK"; rm -f "$list"' EXIT INT TERM HUP
 fi
 
 total=0

tools/gradle-lock.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+# The one-Gradle-build-at-a-time lock (CLAUDE.md › Build and verify). Sourced, not run, by tools/gradle-serial.sh,
+# tools/clean-builds.sh, infra/dev/build.sh and infra/build-images.sh; plain POSIX sh, so sh and bash scripts share it.
+# The lock is a directory holding the pid of its owner; a lock whose owner has died is taken over.
+# shellcheck disable=SC2034  # KVITT_GRADLE_LOCK is used by the scripts that source this file
+KVITT_GRADLE_LOCK=/tmp/kvitt-gradle.lock
+
+# Prints the pid of the live process holding the lock and succeeds; fails when nobody holds it.
+gradle_lock_holder() {
+  _pid=$(cat "$KVITT_GRADLE_LOCK/pid" 2>/dev/null) || return 1
+  [ -n "$_pid" ] && kill -0 "$_pid" 2>/dev/null || return 1
+  printf '%s\n' "$_pid"
+}
+
+# Waits until the lock is free, then takes it for this shell ($$). The caller removes it on exit:
+#   trap 'rm -rf "$KVITT_GRADLE_LOCK"' EXIT INT TERM HUP
+gradle_lock_acquire() {
+  while ! mkdir "$KVITT_GRADLE_LOCK" 2>/dev/null; do
+    _pid=$(cat "$KVITT_GRADLE_LOCK/pid" 2>/dev/null)
+    if [ -n "$_pid" ] && ! kill -0 "$_pid" 2>/dev/null; then rm -rf "$KVITT_GRADLE_LOCK"; continue; fi
+    sleep 5
+  done
+  echo $$ > "$KVITT_GRADLE_LOCK/pid"
+}

tools/gradle-serial.sh

@@ -3,14 +3,10 @@
 # (CLAUDE.md › Build and verify: parallel builds exhaust memory). Waits for a running build to finish, then runs.
 # The Gradle project lives in android/; the wrapper there is used whatever directory this is started from.
 # Usage from any directory of a checkout or worktree:  tools/gradle-serial.sh check   (or ../tools/gradle-serial.sh from android/)
-lock=/tmp/kvitt-gradle.lock
+# shellcheck source-path=SCRIPTDIR source=gradle-lock.sh
+. "$(dirname "$0")/gradle-lock.sh"
 top=$(git rev-parse --show-toplevel) || exit 1
 [ -x "$top/android/gradlew" ] || { echo "gradle-serial: no android/gradlew in $top yet" >&2; exit 1; }
-while ! mkdir "$lock" 2>/dev/null; do
-  pid=$(cat "$lock/pid" 2>/dev/null)
-  if [ -n "$pid" ] && ! kill -0 "$pid" 2>/dev/null; then rm -rf "$lock"; continue; fi
-  sleep 5
-done
-echo $$ > "$lock/pid"
-trap 'rm -rf "$lock"' EXIT INT TERM HUP
+gradle_lock_acquire
+trap 'rm -rf "$KVITT_GRADLE_LOCK"' EXIT INT TERM HUP
 cd "$top/android" && ./gradlew "$@"