feat(channel): implement channel taxonomy

CHANGELOG.md

@@ -11,13 +11,17 @@ All notable changes to this project will be documented in this file.
 * 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.
+* Add opt-in SPSC, SPMC, and MPMC competing queues with topology-specific endpoint capabilities.
+* Add opt-in lossless bounded and unbounded SPMC and MPMC broadcast channels.
+* Add an opt-in latest-state watch channel.
+* Add a `channel` umbrella feature that enables every channel API while keeping their public paths at the crate root.
 
 ### Breaking changes
 
 * Gate all exported primitives behind opt-in Cargo features and enable no features by default; downstream dependencies must explicitly enable the APIs they use.
 * Remove `admission::FairShare` and its `admission` Cargo feature from the feature set.
 * Remove the `asyncband::atomicbox` module and its `AtomicBox` and `AtomicOptionBox` types from the public API.
-* Remove the lossy `broadcast::overflow` channel and its `broadcast` Cargo feature; future broadcast APIs will use explicit bounded and unbounded lossless semantics.
+* Remove the lossy `broadcast::overflow` API; the `broadcast` Cargo feature now selects explicit bounded and unbounded lossless channels.
 * Remove `Semaphore::try_acquire_and_forget`, `Semaphore::acquire_and_forget`, `Semaphore::try_acquire_owned_and_forget`, and `Semaphore::acquire_owned_and_forget`; acquire a permit and call its `forget` method instead.
 * Rename `oneshot::Sender::is_closed` and `oneshot::Receiver::is_closed` to `is_disconnected`.
 * Replace `Semaphore::forget` with `Semaphore::drain_permits` and `Semaphore::forget_exact` with `Semaphore::reduce_permits`; permit-level `forget` methods are unchanged.

HISTORY.md

@@ -9,10 +9,12 @@ Asyncband collects composable, runtime-agnostic concurrency building blocks info
 - `condvar::Condvar` is inspired by [`std::sync::Condvar`](https://doc.rust-lang.org/std/sync/struct.Condvar.html) and [`async_std::sync::Condvar`](https://docs.rs/async-std/latest/async_std/sync/struct.Condvar.html), with a fair FIFO waiter queue and standard non-buffered notification semantics.
 - `latch::Latch` is inspired by [`latches`](https://github.com/mirromutth/latches), with a different implementation based on the internal `CountdownState` primitive.
 - `mutex::Mutex` is derived from [`tokio::sync::Mutex`](https://docs.rs/tokio/latest/tokio/sync/struct.Mutex.html).
+- The cloneable competing-receiver topology of `spmc` and `mpmc` is informed by [`flume`](https://github.com/zesterer/flume), with an independent runtime-agnostic implementation built on Asyncband's waiter arena.
 - `once::OnceCell` is derived from [`tokio::sync::OnceCell`](https://docs.rs/tokio/latest/tokio/sync/struct.OnceCell.html), but uses Asyncband's semaphore implementation.
 - `once::OnceMap` is inspired by [`uv-once-map`](https://github.com/astral-sh/uv/tree/main/crates/uv-once-map), with a redesigned interface and implementation.
 - `oneshot::channel` is derived from the [`oneshot`](https://github.com/faern/oneshot) crate, with significant simplifications because Asyncband does not provide synchronized receive operations.
 - `pool` is ported from [`fastpool`](https://github.com/fast/fastpool), which is derived from [`deadpool`](https://github.com/bikeshedder/deadpool), while keeping Fastpool's runtime-agnostic design and caller-side timeout composition.
 - `rwlock::RwLock` is derived from [`tokio::sync::RwLock`](https://docs.rs/tokio/latest/tokio/sync/struct.RwLock.html), but accepts any `NonZeroUsize` as `max_readers` instead of Tokio's restricted range.
 - `semaphore::Semaphore` is derived from [`tokio::sync::Semaphore`](https://docs.rs/tokio/latest/tokio/sync/struct.Semaphore.html), but omits `close`, avoids Tokio's fixed maximum-permit constant, and adds operations such as `reduce_permits` for Asyncband's use cases.
 - `waitgroup::WaitGroup` is inspired by [`waitgroup-rs`](https://github.com/laizy/waitgroup-rs), with a different API and an implementation based on the internal `CountdownState` primitive.
+- `watch` is inspired by [`tokio::sync::watch`](https://docs.rs/tokio/latest/tokio/sync/watch/), but returns owned `Arc` snapshots instead of runtime-specific borrow guards.

README.md

@@ -54,7 +54,7 @@ async fn increment() {
 }
 ```
 
-Public paths stay direct—such as `asyncband::mutex`, `asyncband::pool`, and `asyncband::once::OnceCell`—while Cargo features keep unused implementations out of the build.
+Public paths stay direct—such as `asyncband::mutex`, `asyncband::mpsc`, and `asyncband::once::OnceCell`—while Cargo features keep unused implementations out of the build. The `channel` feature enables every channel API without adding an `asyncband::channel` namespace.
 
 ## Examples
 
@@ -77,6 +77,12 @@ 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. |
+|                         | [`spsc`](https://docs.rs/asyncband/*/asyncband/spsc/)                                | `spsc`         | Queue each value for one producer and one receiver.                      |
+|                         | [`spmc`](https://docs.rs/asyncband/*/asyncband/spmc/)                                | `spmc`         | Let multiple receivers compete for values from one producer.            |
+|                         | [`mpmc`](https://docs.rs/asyncband/*/asyncband/mpmc/)                                | `mpmc`         | Let multiple producers and receivers share a competing queue.           |
+|                         | [`broadcast::spmc`](https://docs.rs/asyncband/*/asyncband/broadcast/spmc/)           | `broadcast`    | Broadcast every value from one producer to every subscription.          |
+|                         | [`broadcast::mpmc`](https://docs.rs/asyncband/*/asyncband/broadcast/mpmc/)           | `broadcast`    | Broadcast one committed order from concurrent producers.                |
+|                         | [`watch`](https://docs.rs/asyncband/*/asyncband/watch/)                              | `watch`        | Retain the latest state and coalesce intermediate updates.               |
 | 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

@@ -46,9 +46,12 @@ default = []
 
 barrier = []
 blocking = []
+broadcast = []
+channel = ["broadcast", "mpmc", "mpsc", "oneshot", "spmc", "spsc", "watch"]
 condvar = ["mutex"]
 latch = []
 lazy-cell = ["mutex"]
+mpmc = []
 mpsc = []
 mutex = []
 once = ["semaphore"]
@@ -60,7 +63,10 @@ rwlock = []
 semaphore = []
 shutdown = ["latch", "waitgroup"]
 singleflight = ["dep:hashbrown", "once-cell"]
+spmc = []
+spsc = []
 waitgroup = []
+watch = []
 
 [dependencies]
 hashbrown = { workspace = true, default-features = false, features = [