rust/src/libstd/arc.rs

#[doc = "An atomically reference counted wrapper that can be used
hare immutable data between tasks."]

export arc, get, clone;

#[abi = "cdecl"]
native mod rustrt {
    #[rust_stack]
    fn rust_atomic_increment(p: &mut libc::intptr_t)
        -> libc::intptr_t;

    #[rust_stack]
    fn rust_atomic_decrement(p: &mut libc::intptr_t)
        -> libc::intptr_t;
}

type arc_data<T> = {
    mut count: libc::intptr_t,
    data: T
};

resource arc_destruct<T>(data: *arc_data<T>) {
    unsafe {
        let ptr = &mut (*data).count;

        let new_count = rustrt::rust_atomic_decrement(ptr);
        assert new_count >= 0;
        if new_count == 0 {
            let _ptr : ~arc_data<T> = unsafe::reinterpret_cast(data);
            // drop glue takes over.
        }
    }
}

type arc<T> = arc_destruct<T>;

fn arc<T>(-data: T) -> arc<T> {
    let data = ~{mut count: 1, data: data};
    unsafe {
        let ptr = unsafe::reinterpret_cast(data);
        unsafe::forget(data);
        arc_destruct(ptr)
    }
}

fn get<T>(rc: &a.arc<T>) -> &a.T {
    unsafe {
        &(***rc).data
    }
}

fn clone<T>(rc: &arc<T>) -> arc<T> {
    let data = **rc;
    unsafe {
        rustrt::rust_atomic_increment(&mut (*data).count);
    }
    arc_destruct(**rc)
}