Module tokio::sync::mpsc [−][src]
A multi-producer, single-consumer queue for sending values between asynchronous tasks.
This module provides two variants of the channel: bounded and unbounded. The
bounded variant has a limit on the number of messages that the channel can
store, and if this limit is reached, trying to send another message will
wait until a message is received from the channel. An unbounded channel has
an infinite capacity, so the send method will always complete immediately.
This makes the UnboundedSender usable from both synchronous and
asynchronous code.
Similar to the mpsc channels provided by std, the channel constructor
functions provide separate send and receive handles, Sender and
Receiver for the bounded channel, UnboundedSender and
UnboundedReceiver for the unbounded channel. Both Receiver and
UnboundedReceiver implement Stream and allow a task to read
values out of the channel. If there is no message to read, the current task
will be notified when a new value is sent. Sender and
UnboundedSender allow sending values into the channel. If the bounded
channel is at capacity, the send is rejected and the task will be notified
when additional capacity is available. In other words, the channel provides
backpressure.
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 returns 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
When the Receiver is dropped, it is possible for unprocessed messages to
remain in the channel. Instead, it is usually desirable to perform a “clean”
shutdown. To do this, the receiver first calls 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.
Communicating between sync and async code
When you want to communicate between synchronous and asynchronous code, there are two situations to consider:
Bounded channel: If you need a bounded channel, you should use a bounded
Tokio mpsc channel for both directions of communication. Instead of calling
the async send or recv methods, in
synchronous code you will need to use the blocking_send or
blocking_recv methods.
Unbounded channel: You should use the kind of channel that matches where
the receiver is. So for sending a message from async to sync, you should
use the standard library unbounded channel or
crossbeam. Similarly, for sending a message from sync
to async, you should use an unbounded Tokio mpsc channel.
Modules
| error | Channel error types |
Structs
| Permit | Permit to send one value into the channel. |
| Receiver | Receive values from the associated |
| Sender | Send values to the associated |
| UnboundedReceiver | Receive values from the associated |
| UnboundedSender | Send values to the associated |
Functions
| channel | Creates a bounded mpsc channel for communicating between asynchronous tasks with backpressure. |
| unbounded_channel | Creates an unbounded mpsc channel for communicating between asynchronous tasks without backpressure. |