SerialStream is Send on Linux but not Windows

[doylep]

A simple example compiles on Linux but fails on Windows:

use tokio;
use tokio_serial as serial;

#[tokio::main]
async fn main() {
    let builder = serial::new("example/port", 9600);

    if let Ok(stream) = serial::SerialStream::open(&builder) {
        tokio::spawn(async move {
            let _ = stream.writable().await;
        });
    }
}

This fails to compile on Windows with "*mut c_void cannot be shared between threads safely".

Perhaps this is a known limitation? I believe the cause is the difference in internal representation, and the additional "com" struct required for Windows systems. Is there a recommended workaround?

Thanks for your help! And apologies if this was already known.

[edisno]

I have the same problem - it seemed to work before?

[doylep]

Looks like the line in question (line 67 in lib.rs) is 3 years old (commit a0c1cdd), so I imagine it's not a new issue. I only encountered the issue because I'm in the process of porting Linux code to Windows.

Was it working for you recently? Could be an issue caused upstream.

[ndusart]

The issue stems for the usage of raw HANDLE type in serialport::COMPort which is a *mut c_void.

The Send constraint become a Sync constraint on the HANDLE. The issue is on the upstream and they should wrap the HANDLE in a wrapper that is Sync because windows HANDLE are safe to share.

Refer to this issue in winapi defining HANDLE: retep998/winapi-rs#396

[Daniella1]

I am a complete beginner in rust, so this is definitely not the best way to "solve" this. The hack/workaround that worked for me was to clone the tokio-serial repo, then add an unsafe impl for the SerialStream, and then refer to the tokio-stream implementation that you have locally:

1. git clone https://github.com/berkowski/tokio-serial.git
2. Then open the src/lib.rs locally
3. Add this code after the definition of the datatype SerialStream after line 70 (https://github.com/berkowski/tokio-serial/blob/master/src/lib.rs#L57-L70): unsafe impl Sync for SerialStream {}
4. When you want to use your library in the Cargo.toml, update the following

[dependencies]
tokio-serial = {path="path\\to\\your\\library"}