Function Lock

proxy/internal/flock/flock_unix.go:29–58

Lock acquires an exclusive advisory lock on the given file path. It creates the lock file if it does not exist. The lock attempt respects context cancellation by using non-blocking flock with polling. The caller must call Unlock with the returned *os.File when done.

(ctx context.Context, path string)

// respects context cancellation by using non-blocking flock with polling.
// The caller must call Unlock with the returned *os.File when done.
func Lock(ctx context.Context, path string) (*os.File, error) {
	f, err := os.OpenFile(path, os.O_CREATE|os.O_RDWR, 0o600)
	if err != nil {
		return nil, fmt.Errorf("open lock file %s: %w", path, err)
	}

	timer := time.NewTimer(retryInterval)
	defer timer.Stop()

	for {
		if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err == nil {
			return f, nil
		} else if !errors.Is(err, syscall.EWOULDBLOCK) {
			if cerr := f.Close(); cerr != nil {
				log.Debugf("close lock file %s: %v", path, cerr)
			}
			return nil, fmt.Errorf("acquire lock on %s: %w", path, err)
		}

		select {
		case <-ctx.Done():
			if cerr := f.Close(); cerr != nil {
				log.Debugf("close lock file %s: %v", path, cerr)
			}
			return nil, ctx.Err()
		case <-timer.C:
			timer.Reset(retryInterval)
		}
	}
}

// Unlock releases the lock and closes the file.
func Unlock(f *os.File) error {