【Rust】ThreadPoolによる文字検索

全然早くないが使い方間違ってる？

use std::env;
use std::fs;
use std::path::Path;
use std::fs::File;
use std::io::{self, BufRead, BufReader};
use std::time::Instant;
use threadpool::ThreadPool;

fn search_file(filename: String, search_string: String) -> Result<bool, Box<dyn std::error::Error>> {
    for line in BufReader::new(File::open(filename.clone())?).lines() {
        if line.unwrap().contains(&search_string) {
            return Ok(true)
        }
    }
    Ok(false)
}

fn get_files(dirname: &str) -> io::Result<Vec<String>> {
    let mut entries: Vec<String> = Vec::new();
    let dir = Path::new(dirname);
    if dir.is_dir(){
        for entry in fs::read_dir(dirname)? {
            let e = entry?;
            let p = e.path().file_name().unwrap().to_string_lossy().into_owned();
            entries.push(p);
        }
    }
    Ok(entries)
}

fn search_files_sequentially(file_locations: String, search_string: String) {
    let entries: Vec<String> = get_files(&file_locations).unwrap();
    for entry in entries {
        let pass = format!("{}{}", file_locations, entry);
        if search_file(pass, search_string.clone()).unwrap() {
            println!("Found word in file: {}", entry);
        }
    }
}

fn search_files_concurrent(file_locations: String, search_string: String) {
    let entries: Vec<String> = get_files(&file_locations).unwrap();
    let pool = rayon::ThreadPoolBuilder::new().num_threads(4).build().unwrap();
    for entry in entries {
        let pass = format!("{}{}", file_locations, entry);
        let mut value = search_string.clone();
        pool.install(move || {
            if search_file(pass, value).unwrap() {
                println!("Found word in file: {}", entry);
            }
        });
    }
}

fn main(){    
    let now = Instant::now();
    search_files_sequentially("./src/".to_string(), "queue".to_string());
    println!("{:?}", now.elapsed());

    let now = Instant::now();
    search_files_concurrent("./src/".to_string(), "queue".to_string());
    println!("{:?}", now.elapsed());
}

Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
Running `target/debug/parallel queue`
Found word in file: pipeline.rs
Found word in file: main.rs
422.486µs
Found word in file: pipeline.rs
Found word in file: main.rs
701.462µs