You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: FragGeneScanRs.rs
    path of file: ./repos/FragGeneScanRs/src/bin
    
    the code of the file until where you have to start completion: //! FragGeneScanRs executable
#![allow(non_snake_case)]

use std::collections::VecDeque;
use std::fs::File;
use std::io;
use std::io::{Read, Write};
use std::path::PathBuf;
use std::sync::Mutex;

extern crate anyhow;
use anyhow::Result;

extern crate clap;
use clap::{crate_version, App, Arg};

extern crate seq_io;
use seq_io::fasta;

extern crate rayon;
use rayon::iter::{ParallelBridge, 
    
    fn add(&mut self, index: usize, item: Vec<u8>) -> Result<()> {
        while self.next + self.queue.len() <= index {
            self.queue.push_back(None);
        }
        self.queue[index - self.next] = Some(item);

        while self.queue.front().map(Option::is_some).unwrap_or(false) {
            let item = self.queue.pop_front().unwrap().unwrap();
            self.next += 1;
            self.stream.write_all(&item)?;
        }
        Ok(())
    }