Hands-On Concurrency with Rust

crossbeam_epoch::Atomic

Let's dig in with the holder of our data, Atomic. This structure is from the crossbeam_epoch library and its implementation is in src/atomic.rs:

pub struct Atomic<T> {
    data: AtomicUsize,
    _marker: PhantomData<*mut T>,
}

unsafe impl<T: Send + Sync> Send for Atomic<T> {}
unsafe impl<T: Send + Sync> Sync for Atomic<T> {}

The representation is a little odd: why not data: *mut T? Crossbeam's developers have done something neat here. On modern machines, there's a fair bit of space inside of pointer to store information, in the least significant bits. Consider that if we point only to aligned data, the address of a bit of memory will be multiples of 4 on a 32-bit system, or multiples of 8 on a 64-bit system. This leaves either ...