#!/usr/bin/env bash
# Serialises the two things that must not overlap on this Mac: BUILDS (cargo, swiftc, zigbuild, large cross-compiles) and
# MEASUREMENTS (hash-rate samples, millisecond latencies, power: anything a build on the same machine could disturb).
#   tools/lock/with-lock.sh build   <command...>      one of THREE build slots (each build is nice -n 19 with 4 jobs, so
#                                                     three at once use 12 of the 16 cores); waits when all are busy
#   tools/lock/with-lock.sh measure <command...>      exclusive: waits for every build slot and blocks new builds
#   tools/lock/with-lock.sh run     <command...>      a functional run (test network, attack harness, simulator whose
#                                                     outputs are counts, locks, forks, seconds): one of THREE run slots,
#                                                     builds continue; a measurement waits for all of them
#   tools/lock/with-lock.sh status                    who holds what, and for how long
# Rule (4 October 2026): code and documents run in parallel; builds share three slots; measurements are exclusive.
# Evening of 4 October: one build slot and a 3-hour network run under `measure` left twelve agents queued; hence the
# three slots, the `run` mode and `status`. Waits up to 2 hours. This file is replaced atomically (never edited in
# place) because waiting instances are still reading it.
set -euo pipefail
kind="${1:-}"; shift || true
dir=/tmp/igneum-locks; mkdir -p "$dir"
if [ "$kind" = status ]; then
  for f in measure build build-0 build-1 build-2 run-0 run-1 run-2; do
    [ -e "$dir/$f" ] || continue
    holder=$(python3 - "$dir/$f" <<'PY'
import fcntl, sys, os
fd=os.open(sys.argv[1], os.O_RDWR)
try: fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB); fcntl.flock(fd, fcntl.LOCK_UN); print("free")
except BlockingIOError: print("HELD")
PY
)
    printf '%-8s %s' "$f" "$holder"
    if [ "$holder" = HELD ]; then
      # the holder wrote its pid and start time into the lock file
      printf '  %s' "$(tr '\n' ' ' < "$dir/$f" | cut -c1-140)"
    fi
    echo
  done
  echo "waiting:"; ps -eo pid,etime,command | grep -E "[w]ith-lock.sh (build|measure|run) " | grep -v grep | awk '{printf "  %s %s %s %s\n", $1, $2, $4, $5}' | head -20
  exit 0
fi
case "$kind" in
  build)   mode=build;;
  measure) mode=measure;;
  run)     mode=run;;
  *) echo "usage: with-lock.sh build|measure|run <command...> | status" >&2; exit 2;;
esac
# Python holds the locks for the lifetime of this process: it writes the holder line, then execs the command with the
# file descriptors inherited (flock locks follow the open file, so the command keeps them until it exits).
exec python3 - "$mode" "$dir" "$@" <<'PY'
import fcntl, sys, time, os
mode, d = sys.argv[1], sys.argv[2]; cmd = sys.argv[3:]
t0 = time.time()
def opened(name):
    fd = os.open(os.path.join(d, name), os.O_RDWR | os.O_CREAT, 0o644)
    os.set_inheritable(fd, True); return fd
def try_lock(fd):
    try: fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB); return True
    except BlockingIOError: return False
def wait_lock(fd, name):
    while not try_lock(fd):
        if time.time() - t0 > 7200: print(f"with-lock: gave up waiting for {name} after 2 h", file=sys.stderr); sys.exit(1)
        time.sleep(5)
held = []
if mode == 'build':
    # the number of build slots open to NEW builds comes from ~/.config/igneum/build-slots (1 to 3, default 3): 1 when the
    # owner needs the Mac responsive (5 October 2026), builds already running keep their slot
    try: nslots = max(1, min(3, int(open(os.path.expanduser('~/.config/igneum/build-slots')).read().strip())))
    except Exception: nslots = 3
    slots = [opened(f"build-{k}") for k in range(nslots)]
    got = None
    while got is None:
        for k, fd in enumerate(slots):
            if try_lock(fd): got = (k, fd); break
        if got is None:
            if time.time() - t0 > 7200: print("with-lock: gave up waiting for a build slot after 2 h", file=sys.stderr); sys.exit(1)
            time.sleep(5)
    for k, fd in enumerate(slots):
        if got[0] != k: os.close(fd)
    held = [(f"build-{got[0]}", got[1])]
elif mode == 'measure':
    for name in ['measure', 'build', 'build-0', 'build-1', 'build-2', 'run-0', 'run-1', 'run-2']:
        fd = opened(name); wait_lock(fd, name); held.append((name, fd))
else:
    # run: one of THREE run slots (functional runs on their own port ranges can overlap), none while a measurement
    # holds every slot; a measurement waits for every run slot in turn
    slots = [opened(f"run-{k}") for k in range(3)]
    got = None
    while got is None:
        for k, fd in enumerate(slots):
            if try_lock(fd): got = (k, fd); break
        if got is None:
            if time.time() - t0 > 7200: print("with-lock: gave up waiting for a run slot after 2 h", file=sys.stderr); sys.exit(1)
            time.sleep(5)
    for k, fd in enumerate(slots):
        if got[0] != k: os.close(fd)
    held = [(f"run-{got[0]}", got[1])]
for name, fd in held:
    os.ftruncate(fd, 0); os.lseek(fd, 0, 0)
    os.write(fd, f"pid {os.getpid()} since {time.strftime('%H:%M:%S', time.gmtime())}Z waited {int(time.time()-t0)} s: {' '.join(cmd)[:120]}\n".encode())
print(f"with-lock: holding {' '.join(n for n, _ in held)} for: {' '.join(cmd)}", file=sys.stderr)
os.execvp(cmd[0], cmd)
PY