TryMutex<T> should have Send bound on T

[ammaraskar]

Hi there, we (Rust group @sslab-gatech) are scanning crates on crates.io for potential soundness bugs. We noticed that TryMutex implements Sync for all types T:

try-mutex/src/lib.rs

Line 127 in 9775aef

unsafe impl<T> Sync for TryMutex<T> {}

This should probably be bounded by T: Send just like the standard library's Mutex, otherwise it allows smuggling non-Send types like Rc across thread-boundaries like so:

#![forbid(unsafe_code)]

use try_mutex::TryMutex;

use std::rc::Rc;
use crossbeam_utils::thread;

fn main() {
    let rc = Rc::new(());
    let rc_clone = rc.clone();

    let try_mutex = TryMutex::new(rc_clone);
    thread::scope(|s| {    
        s.spawn(|_| {
            let smuggled_rc = try_mutex.try_lock().unwrap();
            println!("RC in thread: {:p}", *smuggled_rc);
        });
    });
    println!("RC in main:   {:p}", rc);
}

This outputs:

RC in thread: 0x5642ef5ffa50
RC in main:   0x5642ef5ffa50

and can lead to data races from safe Rust code.

[mpdn]

Yup, looks like a soundness issue.

Fixed via d2691fd and new 0.3 package.

Thanks.