Check synchronization when using rtrb::Consumer::is_abandoned() about minitrace-rust HOT 3 CLOSED

I see. We don't rely on such assumption on rtrb. Thank you for your advice and your amazing crate!

from minitrace-rust.

Thank you! I think we don't thread synchronization here. The is_abandoned() will eventually return true after the Producer is dropped, right?

from minitrace-rust.

Yes, it will return true eventually ... but ... if you access (read or write) some memory (after the call to is_abandoned()) that has been written to before the Producer was dropped (without any additional synchronization), you are invoking undefined behavior.

This is an illustration of the situation:

static mut V: u32 = 0;
let (p, c) = rtrb::RingBuffer::<u8>::new(7);
let t = std::thread::spawn(move || {
    unsafe { V = 10 };
    drop(p);
});
if c.is_abandoned() {
    std::sync::atomic::fence(std::sync::atomic::Ordering::Acquire);
    unsafe { V = 20 };
}
t.join().unwrap();

Without the fence, this has undefined behavior (but only since Rust 1.74).

AFAIU, this is only a problem if you have unsafe code that relies on the synchronization of is_abandoned() for soundness. In such a case, a fence can be used to restore the synchronization.

from minitrace-rust.