Struct DevChannel 

pub struct DevChannel<T> { /* private fields */ }

The events of a subscription to a device, which unsubscribes when it is dropped: it is a Stream for an asynchronous caller, and Self::wait blocks for a synchronous one.

It gives the latest event and not every one of them, a subscriber that does not keep up skipping to the latest, and never ends. An item that is an error is one event that failed, such as the reading the device was to push, or the subscription failing to be made or being lost.

Subscribing

The subscription is made lazily, the first time the channel is polled, a failure being given as an item like any other. A subscriber that wants to know that it is in place before it waits for events ensures it, see Self::ensure_subscribed_async.

The subscription of a backend lives as long as the connection it was made over, see BackendDev, while the device may be restarted, elsewhere even. The channel holds the proxy of the device for that, which finds it again the way it does for any request: once the subscription is lost, which the backend tells with the very errors a request fails with when its connection is lost, the proxy forgets its connection the way it does for a request, and the channel makes the subscription again through it. The admin device, which subscribing goes through in Tango, is found again along with it: its server is the one of the device, which may have moved with it.

Every attempt is made on the poll after the one that gave the failure of the previous one, so that a subscriber retries as fast as it reads. The events then come back on their own, with no initial value either: read the attribute once the channel gave an error to know where it stands after it.

Implementations

impl<T> DevChannel<T>

pub async fn ensure_subscribed_async(&mut self) -> Result<()>

Make the subscription if it is not in place, giving the failure of the attempt if it failed: the failure is then not given as an item, and the next attempt is made on the next poll.

pub fn ensure_subscribed(&mut self) -> Result<()>

Make the subscription if it is not in place, see Self::ensure_subscribed_async, at most for the timeout of the device.

pub fn wait(&mut self, timeout: Duration) -> Result<T>

Wait for the next event, at most for that long, failing with ErrorKind::TimedOut when none came.

Trait Implementations

impl<T> Debug for DevChannel<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> Stream for DevChannel<T>

type Item = Result<T, Error>

Values yielded by the stream.

fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Option<Self::Item>>

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted.

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream.