feat(broadcast): add unbounded MPMC channel

CHANGELOG.md

@@ -8,6 +8,7 @@ All notable changes to this project will be documented in this file.
 
 ### New features
 
+* Implement `broadcast::mpmc::unbounded`, an unbounded broadcast channel that retains messages until all active receivers consume them or are dropped.
 * Add an opt-in `asyncband::blocking::FutureExt` bridge with `block_on` and `wait_timeout` methods for waiting on runtime-agnostic futures from synchronous code.
 * Add opt-in bounded and unbounded runtime-agnostic object pools under `asyncband::pool`.
 * Add opt-in `asyncband::once::LazyCell` for values that own one asynchronous initializer and preserve its in-flight future across caller cancellation.

Cargo.toml

@@ -35,6 +35,7 @@ asyncband = { path = "asyncband" }
 hashbrown = { version = "0.17.1", default-features = false }
 
 # Dev dependencies
+async-broadcast = { version = "0.7.2" }
 async-channel = { version = "2.5.0" }
 cargo_metadata = { version = "0.23.1" }
 clap = { version = "4.6.5" }

README.md

@@ -77,6 +77,7 @@ Runnable examples live in the [`examples`](examples) workspace crate. They demon
 |                         | [`shutdown`](https://docs.rs/asyncband/*/asyncband/shutdown/)                        | `shutdown`     | Coordinate shutdown signals and completion.                             |
 | Channels                | [`oneshot`](https://docs.rs/asyncband/*/asyncband/oneshot/)                         | `oneshot`      | Send one value between two tasks.                                       |
 |                         | [`mpsc`](https://docs.rs/asyncband/*/asyncband/mpsc/)                               | `mpsc`         | Send values from multiple producers through bounded or unbounded channels. |
+|                         | [`broadcast::mpmc::unbounded`](https://docs.rs/asyncband/*/asyncband/broadcast/mpmc/fn.unbounded.html) | `broadcast`    | Broadcast values from multiple producers and retain them until every active receiver consumes them. |
 | Resource reuse          | [`pool`](https://docs.rs/asyncband/*/asyncband/pool/)                               | `pool`         | Reuse objects through bounded or unbounded pool variants.               |
 | Workload coordination   | [`Semaphore`](https://docs.rs/asyncband/*/asyncband/semaphore/struct.Semaphore.html) | `semaphore`    | Control concurrent access with permits.                                 |
 |                         | [`Group`](https://docs.rs/asyncband/*/asyncband/singleflight/struct.Group.html)      | `singleflight` | Coalesce concurrent calls for the same key.                             |

asyncband/Cargo.toml

@@ -46,6 +46,7 @@ default = []
 
 barrier = []
 blocking = []
+broadcast = []
 condvar = ["mutex"]
 latch = []
 lazy-cell = ["mutex"]

asyncband/src/channel/broadcast/mod.rs

@@ -0,0 +1,20 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Broadcast channels grouped by producer topology.
+
+pub mod mpmc;

asyncband/src/channel/broadcast/mpmc/mod.rs

@@ -0,0 +1,26 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Multi-producer, multi-consumer broadcast channels.
+
+mod unbounded;
+
+pub use self::unbounded::RecvError;
+pub use self::unbounded::TryRecvError;
+pub use self::unbounded::UnboundedReceiver;
+pub use self::unbounded::UnboundedSender;
+pub use self::unbounded::unbounded;