Crate threadbound

  

ThreadBound<T> is a wrapper that binds a value to its original thread. The wrapper gets to be Sync and Send but only the original thread on which the ThreadBound was constructed can retrieve the underlying value.

Example

use std::marker::PhantomData;
use std::rc::Rc;
use std::sync::Arc;
use threadbound::ThreadBound;

// Neither Send nor Sync. Maybe the index points into a
// thread-local interner.
#[derive(Copy, Clone)]
struct Span {
    index: u32,
    marker: PhantomData<Rc<()>>,
}

// Error types are always supposed to be Send and Sync.
// We can use ThreadBound to make it so.
struct Error {
    span: ThreadBound<Span>,
    message: String,
}

fn main() {
    let err = Error {
        span: ThreadBound::new(Span {
            index: 99,
            marker: PhantomData,
        }),
        message: "fearless concurrency".to_owned(),
    };

    // Original thread can see the contents.
    assert_eq!(err.span.get_ref().unwrap().index, 99);

    let err = Arc::new(err);
    let err2 = err.clone();
    std::thread::spawn(move || {
        // Other threads cannot get access. Maybe they use
        // a default value or a different codepath.
        assert!(err2.span.get_ref().is_none());
    });

    // Original thread can still see the contents.
    assert_eq!(err.span.get_ref().unwrap().index, 99);
}

Structs

ThreadBound

ThreadBound is a Sync-maker and Send-maker that allows accessing a value of type T only from the original thread on which the ThreadBound was constructed.