import sun.nio.ch.SimpleAsynchronousFileChannelImpl; //导入依赖的package包/类
/**
 * Constructs an asynchronous file channel by opening the given file.
 */
static AsynchronousFileChannel newAsynchronousFileChannel(UnixPath path,
                                                          Set<? extends OpenOption> options,
                                                          int mode,
                                                          ThreadPool pool)
    throws UnixException
{
    Flags flags = Flags.toFlags(options);

    // default is reading
    if (!flags.read && !flags.write) {
        flags.read = true;
    }

    // validation
    if (flags.append)
        throw new UnsupportedOperationException("APPEND not allowed");

    // for now use simple implementation
    FileDescriptor fdObj = open(-1, path, null, flags, mode);
    return SimpleAsynchronousFileChannelImpl.open(fdObj, flags.read, flags.write, pool);
}