rclrs 0.7.0

A ROS 2 client library for developing robotics applications in Rust
Documentation 
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use std::{ops::Deref, sync::Arc};

use rosidl_runtime_rs::Message;

use crate::{rcl_bindings::*, subscription::SubscriptionHandle, ToResult};

/// A message that is owned by the middleware, loaned out for reading.
///
/// It dereferences to a `&T::RmwMsg`. That is, if `T` is already an RMW-native
/// message, it's the same as `&T`, and otherwise it's the corresponding RMW-native
/// message.
///
/// This type may be used in subscription callbacks to receive a message. The
/// loan is returned by dropping the `ReadOnlyLoanedMessage`.
pub struct ReadOnlyLoanedMessage<T>
where
    T: Message,
{
    pub(super) msg_ptr: *const T::RmwMsg,
    pub(super) handle: Arc<SubscriptionHandle>,
}

impl<T> Deref for ReadOnlyLoanedMessage<T>
where
    T: Message,
{
    type Target = T::RmwMsg;
    fn deref(&self) -> &Self::Target {
        unsafe { &*self.msg_ptr }
    }
}

impl<T> Drop for ReadOnlyLoanedMessage<T>
where
    T: Message,
{
    fn drop(&mut self) {
        unsafe {
            rcl_return_loaned_message_from_subscription(
                &*self.handle.lock(),
                self.msg_ptr as *mut _,
            )
            .ok()
            .unwrap();
        }
    }
}

// SAFETY: The functions accessing this type, including drop(), shouldn't care about the thread
// they are running in. Therefore, this type can be safely sent to another thread.
unsafe impl<T> Send for ReadOnlyLoanedMessage<T> where T: Message {}
// SAFETY: This type has no interior mutability, in fact it has no mutability at all.
unsafe impl<T> Sync for ReadOnlyLoanedMessage<T> where T: Message {}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn traits() {
        use crate::{test_helpers::*, vendor::test_msgs};

        assert_send::<ReadOnlyLoanedMessage<test_msgs::msg::rmw::BoundedSequences>>();
        assert_sync::<ReadOnlyLoanedMessage<test_msgs::msg::rmw::BoundedSequences>>();
    }
}