Rongsong Shen
980a0054d1
Two xce-build.sh runs against the same build dir raced: one run's
setup_build rm -rf hit files the other was writing ('Directory not
empty'), or deleted a binary the other had just built and tested.
xce-build.sh now takes an exclusive per-build-dir lock right after cd-ing
into src/ and holds it until it exits; a second run against the same dir
waits, runs against different dirs are unaffected. The lock
(src/tools/build-lock.sh) is an mkdir lock holding the owner PID, outside
the build dir, keyed by a hash of its absolute path; it needs only
coreutils (the nix dev shell has no flock) and takes over a lock whose
owner died. src/tools/test-build-lock.sh tests it.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
59 lines
2.3 KiB
Bash
59 lines
2.3 KiB
Bash
# build-lock.sh — exclusive per-build-dir lock for xce-build.sh (bug-1604).
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#
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# Sourced, not executed. Two xce-build.sh runs against the SAME build dir used
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# to race: one run's `rm -rf $BUILD_DIR` hit files the other was writing
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# ("Directory not empty") or silently deleted a binary the other had just
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# built and tested. The lock serializes them for the whole run (wipe, setup,
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# compile, tests); runs against DIFFERENT build dirs stay concurrent.
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#
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# The lock is a directory created with mkdir (atomic; needs nothing beyond
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# coreutils, unlike flock(1), which the nix dev shell does not provide),
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# holding the owner's PID. It lives outside the build dir -- the wipe would
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# delete it -- under $XCE_BUILD_LOCK_ROOT (default $TMPDIR or /tmp), named
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# after a hash of the build dir's absolute path, so separate checkouts never
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# share a lock. A lock whose owner is no longer running (a build killed with
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# SIGKILL) is taken over.
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#
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# build_lock_acquire <build_dir> blocks until held
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# build_lock_release releases it (safe to call twice)
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#
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# Tunables: XCE_BUILD_LOCK_ROOT, XCE_BUILD_LOCK_POLL_SECS (default 2).
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BUILD_LOCK_DIR=""
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build_lock_path() {
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local abs sum
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abs="$(realpath -m -- "$1")"
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sum="$(printf '%s' "$abs" | cksum | cut -d' ' -f1)"
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printf '%s/xce-build-%s.lock' "${XCE_BUILD_LOCK_ROOT:-${TMPDIR:-/tmp}}" "$sum"
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}
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build_lock_acquire() {
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local lock owner waited=0 poll="${XCE_BUILD_LOCK_POLL_SECS:-2}"
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lock="$(build_lock_path "$1")"
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while ! mkdir "$lock" 2>/dev/null; do
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owner="$(cat "$lock/pid" 2>/dev/null || true)"
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if [ -n "$owner" ] && ! kill -0 "$owner" 2>/dev/null; then
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# The owner died holding it. If two waiters take over the same
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# stale lock at once, mkdir below still lets only one of them in.
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echo "=== Build lock for $1 was left by PID $owner, which is gone -- taking it over ===" >&2
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rm -rf -- "$lock"
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continue
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fi
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if [ "$waited" = 0 ]; then
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echo "=== Waiting for another xce-build.sh run (PID ${owner:-?}) to finish with $1 ... ===" >&2
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waited=1
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fi
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sleep "$poll"
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done
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echo "${BASHPID:-$$}" > "$lock/pid"
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BUILD_LOCK_DIR="$lock"
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}
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build_lock_release() {
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if [ -n "$BUILD_LOCK_DIR" ]; then
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rm -rf -- "$BUILD_LOCK_DIR"
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BUILD_LOCK_DIR=""
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fi
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}
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