@Override
  public <A> void lock(
      long position,
      long size,
      boolean shared,
      @Nullable A attachment,
      CompletionHandler<FileLock, ? super A> handler) {
    checkNotNull(handler);
    addCallback(lock(position, size, shared), handler, attachment);
  }
{@link AsynchronousFileChannel} implementation that delegates to a {@link JimfsFileChannel}.

@author Colin Decker
jimfs/src/main/java/com/google/common/jimfs/JimfsAsynchronousFileChannel.java