kovan 0.1.3

What is Kovan?

Kovan solves the hardest problem in lock-free programming: when is it safe to free memory?

When multiple threads access shared data without locks, you can't just drop() or free() - another thread might still be using it. Kovan tracks this automatically with zero overhead on reads.

Why Kovan?

• Zero read overhead: Just one atomic load, nothing else
• Bounded memory: Never grows unbounded like epoch-based schemes
• Simple API: Three functions: pin(), load(), retire()

Quick Start

[dependencies]
kovan = "0.1"

Basic Usage

use kovan::{Atomic, pin, retire};
use std::sync::atomic::Ordering;

// Create shared atomic pointer
let shared = Atomic::new(Box::into_raw(Box::new(42)));

// Read safely
let guard = pin();  // Enter critical section
let ptr = shared.load(Ordering::Acquire, &guard);
unsafe {
    if let Some(value) = ptr.as_ref() {
        println!("Value: {}", value);
    }
}
drop(guard);  // Exit critical section

// Update safely
let guard = pin();
let new_value = Box::into_raw(Box::new(100));
let old = shared.swap(
    unsafe { kovan::Shared::from_raw(new_value) },
    Ordering::Release,
    &guard
);

// Schedule old value for reclamation
if !old.is_null() {
    unsafe { retire(old.as_raw()); }
}

How It Works

1. pin() - Enter critical section, get a guard
2. load() - Read pointer (zero overhead!)
3. retire() - Schedule memory for safe reclamation

The guard ensures any pointers you load stay valid. When all guards are dropped, retired memory is freed automatically.

Examples

See the examples/ directory for complete implementations:

• simple.rs - Basic usage patterns
• treiber_stack.rs - Lock-free stack implementation

Run examples:

cargo run --example simple
cargo run --example treiber_stack

Key Rules

1. Always use a guard when accessing shared pointers
2. Retire, don't drop - use retire() instead of Box::from_raw()
3. Add RetiredNode as first field in your structs

Performance

• 10x faster than naive implementations
• Competitive with Crossbeam-Epoch on reads
• Better memory bounds than epoch-based schemes

Optional Features

# Nightly optimizations (~5% faster)
kovan = { version = "0.1", features = ["nightly"] }

# Handle stalled threads
kovan = { version = "0.1", features = ["robust"] }

License

Licensed under either of Apache License 2.0 or MIT license at your option.