The feature-rich, portable async channel library > crates.io > docs.rs

Why use Postage?

• Includes a rich set of channels. | barrier | broadcast | dispatch | mpsc | oneshot | watch
• Works with any executor.
  • Currently regressions are written for tokio and async-std.
  • With the futures-traits feature, channels implement the futures Sink/Stream traits.
• Thoroughly tested.
  • Channels have full unit test coverage, and integration test coverage with multiple async executors.
• Includes built-in Sink and Stream combinators.
  • Sinks can be chained and filtered.
  • Streams can be chained, filtered, mapped, and merged.
  • Sinks and streams can log their values, for easy app debugging.

Channels

postage::barrier

Barrier channels can be used to synchronize events, but do not transmit any data. When the sender is dropped (or tx.send(()) is called), the receiver is awoken. This can be used to asynchronously coordinate actions between tasks.

postage::broadcast

The broadcast channel provides reliable broadcast delivery between multiple senders and multiple receivers. The channel has a fixed capacity, and senders are suspended if the buffer is filled.

When a receiver is cloned, both receivers will be sent the same series of messages.

Senders also provide a subscribe() method which creates a receiver that will observe all messages sent after the call to subscribe.

postage::dispatch

The dispatch channel provides multi-sender, multi-receiver message dispatch. A message will be observed by at most one reciever. The channel has a fixed capacity, and senders are suspended if the buffer is filled.

Receivers can be created with rx.clone(), or tx.subscribe().

postage::mpsc

Postage includes a fixed-capacity multi-producer, single-consumer channel. The producer can be cloned, and the sender task is suspended if the channel becomes full.

postage::oneshot

Oneshot channels transmit a single value between a sender and a reciever. Neither can be cloned. If the sender drops, the receiver recieves a None value.

postage::watch

Watch channels can be used to asynchronously transmit state. When receivers are created, they immediately recieve an initial value. They will also recieve new values, but are not guaranteed to recieve every value.

Values transmitted over watch channels must implement Default. A simple way to achieve this is to transmit Option<T>.

Benchmarks

Benchmarks of postage channels, and comparable async-std/tokio channels.

• send/recv measures the total time to send and receive an item.
• send full measures the time to send an item and get a Poll::Pending value on a full channel.
• recv empty measures the time to get a Poll::Pending value on an empty channel.

All benchmarks were taken with criterion and are in the benches directory.

Package	Channel	send/recv	send full	recv empty
broadcast	postage	114ns	7ns	8ns
broadcast	tokio	98ns (-14%)	54ns	37ns
-
dispatch	postage	80ns	26ns	25ns
dispatch	async_std	41ns (-48%)	10ns	11ns
-
mpsc	postage	83ns	27ns	30ns
mpsc	tokio	85ns (+1%)	2ns	35ns
-
watch	postage	96ns	-	7ns
watch	tokio	73ns (-23%)	-	75ns