semrs

This is a dependency-free, pure Rust implementation of counting semaphores.

Crates.io: https://crates.io/crates/semrs.

GitHub repository: https://github.com/obicons/semrs.

Getting Started

cargo add semrs

Or add the following line to your Cargo.toml:

semrs = "0.5.2"

About

Unfortunately, the use of semaphores often requires unsafe blocks. Fundamentally, a semaphore does not provide exclusive access. It provides limited access. It's up to the programmer to ensure that the access is ultimately free from dataraces.

The semaphore is a useful concurrency primitive despite this severe limitation. For example, semaphores can be used to implement a bounded buffer to solve the readers/writers problem without busy-waiting. Semaphores are useful for implementing safe concurrency primitives.

Usage

// Two references to a binary semaphore.
let s1 = Arc::new(Semaphore::new(1));
let s2 = s1.clone();

// A shared resource, r, and a pointer to it, p.
let mut r = UnsafeCell::new(0);
let p: usize = r.get() as usize;

// Thread 1.
let t1 = std::thread::spawn(move || {
    s1.down();
    let p: *mut i32 = p as *mut i32;
    unsafe { *p += 1; }
    s1.up();
});

// Thread 2.
let t2 = std::thread::spawn(move || {
    s2.down();
    let p: *mut i32 = p as *mut i32;
    unsafe { *p += 1; }
    s2.up();
});

let _ = t1.join();
let _ = t2.join();

// The access was sychronized.
assert!(*r.get_mut() == 2);