file-api.rs

// use file api
use anyhow::Result;
use std::fs::OpenOptions;
use std::io::{self, Write, Seek, SeekFrom};
use std::thread;

fn write_to_file_at_position(file_path: &str, data: &[u8], position: u64) -> io::Result<()> {
    // Open the file in write mode and create it if it doesn't exist
    let mut file = OpenOptions::new()
        .write(true)
        .create(true)
        .open(file_path)?;

    // Move the file cursor to the specified position
    file.seek(SeekFrom::Start(position))?;

    // Write the data to the file
    file.write_all(data)?;

    Ok(())
}

fn main() -> Result<()> {
    let file_path = "example.txt";
    let data1 = b"Thread 1: Hello, World!";
    let data2 = b"Thread 2: Rust is awesome!";
    let position1 = 0;
    let position2 = 23;

    // Spawn two threads, each performing a write operation
    let thread1 = thread::spawn(move || {
        write_to_file_at_position(file_path, data1, position1)
    });

    let thread2 = thread::spawn(move || {
        write_to_file_at_position(file_path, data2, position2)
    });

    // Wait for both threads to finish
    thread1.join().unwrap()?;
    thread2.join().unwrap()?;

    Ok(())
}

mmap.rs

// use mmap
use anyhow::Result;
use memmap2::MmapOptions;
use std::fs::OpenOptions;
use std::thread;

fn main() -> Result<()> {
    // Open or create a file
    let file_path = "example.txt";
    let file = OpenOptions::new()
        .read(true)
        .write(true)
        .create(true)
        .open(file_path)?;

    // Set the file size
    file.set_len(49)?;

    // Create a memory map for the first region (unsafe)
    let mut mmap1 = unsafe {
        MmapOptions::new().map_mut(&file)?
    };

    // Create a memory map for the second region (unsafe)
    let mut mmap2 = unsafe {
        MmapOptions::new().map_mut(&file)?
    };

    // Schedule writes to different non-overlapping parts of the mmapped file
    let thread1 = thread::spawn(move || {
        let data = b"Thread 1: Hello, World!";
        let position = 0;
        mmap1[position..position + data.len()].copy_from_slice(data);
    });

    let thread2 = thread::spawn(move || {
        let data = b"Thread 2: Rust is awesome!";
        let position = 23;
        mmap2[position..position + data.len()].copy_from_slice(data);
    });

    // Wait for both threads to finish
    thread1.join().unwrap();
    thread2.join().unwrap();
    Ok(())
}