reqchan 0.5.8

This is a channel for requesting and receiving data. Each channel has only one requesting end, but it can have multiple responding ends. It is useful for implementing work sharing. The two ends of the channel are asynchronous with respect to each other, so it is kinda nonblocking. However, if multiple responding ends try to respond to the same request, only one will succeed; the rest will return errors.
Documentation 
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use std::sync::Arc;
use std::sync::atomic::{AtomicUsize, Ordering};

extern crate reqchan;
use reqchan::*;

trait FnBox {
    fn call_box(self: Box<Self>);
}

impl<F: FnOnce()> FnBox for F {
    fn call_box(self: Box<F>) {
        (*self)()
    }
}

type Task = Box<FnBox + Send + 'static>;

#[test]
fn test_multiple_requests() {
    let (rqst, resp) = channel::<Task>();

    let var = Arc::new(AtomicUsize::new(0));
    let var2 = var.clone();
    let var3 = var.clone();

    // Scope of first set of contracts
    {
        let mut rqst_con = rqst.try_request().unwrap();
        let resp_con = resp.try_respond().unwrap();

        resp_con.send(Box::new(move || {
            var2.fetch_add(1, Ordering::SeqCst);
        }) as Task);

        match rqst_con.try_receive() {
            Ok(task) => {
                task.call_box();
            },
            _ => { assert!(false); },
        }
        // `resp_con` should drop here freeing up `resp` 
        // `rqst_con` should drop here freeing up `rqst` 
    }

    assert_eq!(var.load(Ordering::SeqCst), 1);

    // Scope of second set of contracts
    {
        let mut rqst_con = rqst.try_request().unwrap();
        let resp_con = resp.try_respond().unwrap();

        resp_con.send(Box::new(move || {
            var3.fetch_add(1, Ordering::SeqCst);
        }) as Task);

        match rqst_con.try_receive() {
            Ok(task) => {
                task.call_box();
            },
            _ => { assert!(false); },
        }
        // `resp_con` should drop here freeing up `resp` 
        // `rqst_con` should drop here freeing up `rqst` 
    }

    assert_eq!(var.load(Ordering::SeqCst), 2);
}

#[test]
fn test_multiple_responders() {
    let (rqst, resp) = channel::<Task>();
    let resp2 = resp.clone();

    let var = Arc::new(AtomicUsize::new(0));
    let var2 = var.clone();
    
    let mut rqst_con = rqst.try_request().unwrap();
    let resp_con = resp.try_respond().unwrap();

    match resp2.try_respond() {
        Err(TryRespondError::Locked) => {},
        _ => { assert!(false); },
    }

    resp_con.send(Box::new(move || {
        var2.fetch_add(1, Ordering::SeqCst);
    }) as Task);

    match rqst_con.try_receive() {
        Ok(task) => {
            task.call_box();
        },
        _ => { assert!(false); },
    }

    assert_eq!(var.load(Ordering::SeqCst), 1);
}