Module futures::channel::mpsc

Expand description

A multi-producer, single-consumer queue for sending values across asynchronous tasks.

Similarly to the std, channel creation provides Receiver and Sender handles. Receiver implements Stream and allows a task to read values out of the channel. If there is no message to read from the channel, the current task will be notified when a new value is sent. Sender implements the Sink trait and allows a task to send messages into the channel. If the channel is at capacity, the send will be rejected and the task will be notified when additional capacity is available. In other words, the channel provides backpressure.

Unbounded channels are also available using the unbounded constructor.

Disconnection

When all Sender handles have been dropped, it is no longer possible to send values into the channel. This is considered the termination event of the stream. As such, Receiver::poll_next will return Ok(Ready(None)).

If the Receiver handle is dropped, then messages can no longer be read out of the channel. In this case, all further attempts to send will result in an error.

Clean Shutdown

If the Receiver is simply dropped, then it is possible for there to be messages still in the channel that will not be processed. As such, it is usually desirable to perform a “clean” shutdown. To do this, the receiver will first call close, which will prevent any further messages to be sent into the channel. Then, the receiver consumes the channel to completion, at which point the receiver can be dropped.