mozilla-central/third_party/rust/tokio/src/sync/mpsc
Name Description Size
block.rs 15244
bounded.rs 64469
chan.rs 18060
error.rs Channel error types. 4242
list.rs A concurrent, lock-free, FIFO list. 13102
mod.rs 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. 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. This channel is also suitable for the single-producer single-consumer use-case. (Unless you only need to send one message, in which case you should use the [oneshot] channel.) # 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. Additionally, all unread messages will be drained from the channel and dropped. # 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`][bounded-send] or [`recv`][bounded-recv] methods, in synchronous code you will need to use the [`blocking_send`][blocking-send] or [`blocking_recv`][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][std-unbounded] or [crossbeam][crossbeam-unbounded]. Similarly, for sending a message _from sync to async_, you should use an unbounded Tokio `mpsc` channel. Please be aware that the above remarks were written with the `mpsc` channel in mind, but they can also be generalized to other kinds of channels. In general, any channel method that isn't marked async can be called anywhere, including outside of the runtime. For example, sending a message on a [oneshot] channel from outside the runtime is perfectly fine. # Multiple runtimes The mpsc channel does not care about which runtime you use it in, and can be used to send messages from one runtime to another. It can also be used in non-Tokio runtimes. There is one exception to the above: the [`send_timeout`] must be used from within a Tokio runtime, however it is still not tied to one specific Tokio runtime, and the sender may be moved from one Tokio runtime to another. [`Sender`]: crate::sync::mpsc::Sender [`Receiver`]: crate::sync::mpsc::Receiver [bounded-send]: crate::sync::mpsc::Sender::send() [bounded-recv]: crate::sync::mpsc::Receiver::recv() [blocking-send]: crate::sync::mpsc::Sender::blocking_send() [blocking-recv]: crate::sync::mpsc::Receiver::blocking_recv() [`UnboundedSender`]: crate::sync::mpsc::UnboundedSender [`UnboundedReceiver`]: crate::sync::mpsc::UnboundedReceiver [oneshot]: crate::sync::oneshot [`Handle::block_on`]: crate::runtime::Handle::block_on() [std-unbounded]: std::sync::mpsc::channel [crossbeam-unbounded]: https://docs.rs/crossbeam/*/crossbeam/channel/fn.unbounded.html [`send_timeout`]: crate::sync::mpsc::Sender::send_timeout 5635
unbounded.rs 23985