Rust Mutex and RwLock

In Rust's concurrent programming model, Mutex and RwLock are essential synchronization primitives. They ensure safe access to shared data across multiple threads, preventing race conditions and data corruption.

Mutex (Mutual Exclusion)

A Mutex allows only one thread to access the data at a time. It's ideal for scenarios where you need exclusive access to a resource.

Basic Usage

use std::sync::{Arc, Mutex};
use std::thread;

fn main() {
    let counter = Arc::new(Mutex::new(0));
    let mut handles = vec![];

    for _ in 0..10 {
        let counter = Arc::clone(&counter);
        let handle = thread::spawn(move || {
            let mut num = counter.lock().unwrap();
            *num += 1;
        });
        handles.push(handle);
    }

    for handle in handles {
        handle.join().unwrap();
    }

    println!("Result: {}", *counter.lock().unwrap());
}
    

In this example, we use a Mutex to safely increment a counter across multiple threads.

RwLock (Read-Write Lock)

An RwLock allows multiple readers or a single writer to access the data. It's useful when you have data that is frequently read but infrequently modified.

Basic Usage

use std::sync::{Arc, RwLock};
use std::thread;

fn main() {
    let data = Arc::new(RwLock::new(vec![1, 2, 3]));
    let mut handles = vec![];

    // Reader threads
    for _ in 0..3 {
        let data = Arc::clone(&data);
        handles.push(thread::spawn(move || {
            let numbers = data.read().unwrap();
            println!("Read: {:?}", *numbers);
        }));
    }

    // Writer thread
    {
        let data = Arc::clone(&data);
        handles.push(thread::spawn(move || {
            let mut numbers = data.write().unwrap();
            numbers.push(4);
            println!("Write: {:?}", *numbers);
        }));
    }

    for handle in handles {
        handle.join().unwrap();
    }
}
    

This example demonstrates how RwLock allows multiple reader threads to access the data concurrently, while ensuring exclusive access for the writer thread.

Key Considerations

• Use Mutex when you need exclusive access to data.
• Prefer RwLock when you have mostly read operations and occasional writes.
• Be cautious of deadlocks when using multiple locks.
• Remember to release locks as soon as possible to improve concurrency.
• Use Arc (Atomic Reference Counting) to share ownership across threads.

Related Concepts

To fully understand Mutex and RwLock in Rust, it's helpful to explore these related topics:

• Rust Threads
• Rust Shared State
• Rust Sync and Send Traits
• Rust Atomic Types

By mastering these synchronization primitives, you'll be well-equipped to write safe and efficient concurrent Rust programs.