Function acquireServerLock

browse/src/cli.ts:379–402

* Acquire an exclusive lockfile to prevent concurrent ensureServer() races (TOCTOU). * Returns a cleanup function that releases the lock.

()

 * Returns a cleanup function that releases the lock.
 */
function acquireServerLock(): (() => void) | null {
  const lockPath = `${config.stateFile}.lock`;
  try {
    // 'wx' — create exclusively, fails if file already exists (atomic check-and-create)
    // Using string flag instead of numeric constants for Bun Windows compatibility
    const fd = fs.openSync(lockPath, 'wx');
    fs.writeSync(fd, `${process.pid}\n`);
    fs.closeSync(fd);
    return () => { safeUnlink(lockPath); };
  } catch {
    // Lock already held — check if the holder is still alive
    try {
      const holderPid = parseInt(fs.readFileSync(lockPath, 'utf8').trim(), 10);
      if (holderPid && isProcessAlive(holderPid)) {
        return null; // Another live process holds the lock
      }
      // Stale lock — remove and retry
      fs.unlinkSync(lockPath);
      return acquireServerLock();
    } catch {
      return null;
    }
  }
}

async function ensureServer(flags?: GlobalFlags): Promise<ServerState> {
  const state = readState();