cbus::Message::new is missing Send bound on callback

Since callback is executed in different thread it must implement Send. Otherwise you can easily cause havoc by passing thread unsafe primitives like Rc.

Code: https://git.picodata.io/picodata/picodata/tarantool-module/-/blob/master/tarantool/src/cbus/mod.rs#L99

cc @k.derevtsov, I'm assigning this to you, but let me know if you need any help with that. Please mention me in MR when you'll make a patch

assigned to @k.derevtsov

Let me explain with a little bit more details. What Send bound means? It means that object that implements it is fine with moving it to another thread. Note that this is not the same as Sync, sync guarantee is more demanding, it requires that it is safe to access the object from different threads. Compared to that Send is rather simple. Many objects are safe to pass to another thread. But which objects are not safe to pass to another thread?

The canonical example would be Rc. Why it is not Send? Because reference counter in Rc is not atomic. So with current API multiple threads can update it without synchronization. This can lead to use after free vulnerability if one thread sees stale ref count equal to 1.

Basically the following shouldnt compile:

pub fn non_send() {
    let data = Rc::new(8);
    let cloned = Rc::clone(&data);
    let m = Message::new(move || println!("Rc: {}", cloned));

    println!("Rc: {}", data)
}

it sounds reasonable, i'm try to create an MR asap

Thank you! Let me know if you need any help

mentioned in commit 721893cc

mentioned in commit d54c5982

mentioned in merge request !415 (merged)

mentioned in commit 65ad75c6

mentioned in commit 35fec722

mentioned in commit 24df264b

mentioned in commit eb93bec8

mentioned in commit 33ec71b2

mentioned in commit 8f0dab5f

mentioned in commit 9e588514

closed with merge request !415 (merged)

closed with commit 9e588514