Struct CallbackStream

pub struct CallbackStream<T: 'static>(/* private fields */);

Type-erased stream sender.

Use this to wrap a Sender into a data structure that may be passed via a c_void pointer as user data to an external library. Later, when this extern callback is run with that data, we may unwrap it and can thus send messages into the stream or close the stream.

The implementation uses associated methods:

• CallbackStream::prepare() to wrap the stream sender and get the c_void pointer
• CallbackStream::notify() to use the c_void pointer and send messages to the stream
• CallbackStream::delete() to unwrap the c_void pointer and close the underlying stream

Examples

use futures::executor::block_on;
use open62541::CallbackStream;
use tokio::sync::mpsc;

let (tx, mut rx) = mpsc::channel::<u32>(10);

// Turn `tx` into type-erased void pointer for FFI.
let raw_data: *mut c_void = CallbackStream::<u32>::prepare(tx);

// Use type-erased pointer to send messages.
unsafe { CallbackStream::<u32>::notify(raw_data, 1); }
unsafe { CallbackStream::<u32>::notify(raw_data, 2); }
unsafe { CallbackStream::<u32>::notify(raw_data, 3); }

// Clean up resources held by pointer.
unsafe { CallbackStream::<u32>::delete(raw_data); }

// Values have been received.
assert_eq!(block_on(rx.recv()), Some(1));
assert_eq!(block_on(rx.recv()), Some(2));
assert_eq!(block_on(rx.recv()), Some(3));
assert_eq!(block_on(rx.recv()), None);

Implementations

impl<T> CallbackStream<T>

pub fn prepare(tx: Sender<T>) -> *mut c_void

Prepares sender for later use.

This allocates memory. To prevent memory leaks, call delete() on the returned pointer exactly once.

pub unsafe fn notify(data: *mut c_void, payload: T)

Uses c_void pointer and sends message.

Safety

The given pointer must have been returned from prepare() and must not have been passed into delete() yet.

The value type T must be the same as in prepare().

pub unsafe fn delete(data: *mut c_void)

Unwraps c_void pointer and closes channel.

Safety

The given pointer must have been returned from prepare() and must not have been passed into delete() yet.

Trait Implementations

impl<T: Debug + 'static> Debug for CallbackStream<T>

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

Formats the value using the given formatter.