Moving Arc<RwLock<T>> to threads leads to errors regarding missing Send trait

[AngryPixelShader]

Hello,

I'm having some issues understanding why this is a problem. When I try to move an Arc<RwLock<T> to a thread I get a long error message that the Send trait is not implemented for T and all the members of T as well.

note: required by a bound in `spawn`
    |
625 |     F: Send + 'static,
    |        ^^^^ required by this bound in `spawn`

Here's a snippet of code where this happens:

pub(crate) fn new(swap_chains: Arc<RwLock<SwapChainMap>>) -> Self {
  let (thread_sender, thread_receiver) = std::sync::mpsc::channel::<PresentMessage>();
  let (response_sender, response_receiver) = std::sync::mpsc::channel::<PresentResultMessage>();
  let child = std::thread::spawn(move || loop {  // <-- error here
    // access swap_chains with write/read
    // send/receive messages  
  });
...
}

SwapChainMap is typedef for a custom map structure (pub struct HandleMap<H, T>) and I'm using the 1.57.0 nightly compiler.

Shouldn't this just work? I was under the impression that RwLock provides Send and Sync implementations. Am I missing something?

[mejrs]

H and T are not necessarily Send, though. Or 'static, for that matter. Rwlock and Arc can't "wrap" something to make it Send. As such you need a Send bound on them as well.

[Cerber-Ursi]

@AngryPixelShader

I was under the impression that RwLock provides Send and Sync implementations.

RwLock is Send only if the underlying value is Send (and same for Sync). Arc is Sync if the underlying value is Send.

[AngryPixelShader]

Ah I see. Thanks for the info!