feat(phaser): add reusable phase coordination

CHANGELOG.md

@@ -27,6 +27,7 @@ All notable changes to this project will be documented in this file.
 * 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 bounded and unbounded runtime-agnostic object pools under `asyncband::pool`.
 * 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 an opt-in runtime-agnostic `Phaser` with dynamic RAII participants, reusable phases, and cancellation-resilient arrival semantics.
 
 ### Bug fixes
 

README.md

@@ -75,6 +75,7 @@ Runnable examples live in the [`examples`](examples) workspace crate. They demon
 |                            | [`Completion`](https://docs.rs/asyncband/*/asyncband/completion/struct.Completion.html)       | `completion`   | Publish one shared result to any number of current and future observers.                                       |
 |                            | [`ManualResetEvent`](https://docs.rs/asyncband/*/asyncband/event/struct.ManualResetEvent.html) | `event`        | Signal current and future waits until explicitly reset.                                                       |
 |                            | [`Latch`](https://docs.rs/asyncband/*/asyncband/latch/struct.Latch.html)                       | `latch`        | Wait until a fixed one-way countdown reaches zero.                                                            |
+|                            | [`Phaser`](https://docs.rs/asyncband/*/asyncband/phaser/struct.Phaser.html)                    | `phaser`       | Coordinate repeated phases with a dynamic participant set.                                                    |
 |                            | [`WaitGroup`](https://docs.rs/asyncband/*/asyncband/waitgroup/struct.WaitGroup.html)           | `waitgroup`    | Wait until all cloned worker handles are dropped.                                                             |
 |                            | [`Shutdown`](https://docs.rs/asyncband/*/asyncband/shutdown/struct.Shutdown.html)              | `shutdown`     | Request shutdown and wait until all completion guards are dropped.                                            |
 | Channels                   | [`oneshot`](https://docs.rs/asyncband/*/asyncband/oneshot/)                                    | `oneshot`      | Send one value from one sender to one receiver.                                                               |

asyncband/Cargo.toml

@@ -58,6 +58,7 @@ once = ["semaphore"]
 once-cell = ["semaphore"]
 once-map = ["dep:hashbrown", "once-cell"]
 oneshot = []
+phaser = []
 pool = ["semaphore"]
 rwlock = []
 semaphore = []
@@ -73,6 +74,7 @@ hashbrown = { workspace = true, default-features = false, features = [
 
 [dev-dependencies]
 tokio = { workspace = true, features = ["full"] }
+tokio-test = { workspace = true }
 
 [lints]
 workspace = true

asyncband/src/internal/mod.rs

@@ -26,6 +26,7 @@ pub(crate) mod atomic_waker;
     feature = "latch",
     feature = "mpsc",
     feature = "mutex",
+    feature = "phaser",
     feature = "rwlock",
     feature = "semaphore",
     feature = "waitgroup",
@@ -56,6 +57,7 @@ pub(crate) mod value_cell;
     feature = "latch",
     feature = "mpsc",
     feature = "mutex",
+    feature = "phaser",
     feature = "rwlock",
     feature = "semaphore",
     feature = "waitgroup",
@@ -94,6 +96,7 @@ pub(crate) mod waitlist;
     feature = "completion",
     feature = "latch",
     feature = "once",
+    feature = "phaser",
     feature = "waitgroup",
     feature = "watch",
 ))]

asyncband/src/lib.rs

@@ -67,6 +67,7 @@
 //! |                            | [`Completion`](completion::Completion)       | `completion`   | Publish one shared result to any number of current and future observers.                                       |
 //! |                            | [`ManualResetEvent`](event::ManualResetEvent) | `event`        | Signal current and future waits until explicitly reset.                                                       |
 //! |                            | [`Latch`](latch::Latch)                       | `latch`        | Wait until a fixed one-way countdown reaches zero.                                                            |
+//! |                            | [`Phaser`](phaser::Phaser)                    | `phaser`       | Coordinate repeated phases with a dynamic participant set.                                                    |
 //! |                            | [`WaitGroup`](waitgroup::WaitGroup)           | `waitgroup`    | Wait until all cloned worker handles are dropped.                                                             |
 //! |                            | [`Shutdown`](shutdown::Shutdown)              | `shutdown`     | Request shutdown and wait until all completion guards are dropped.                                            |
 //! | Channels                   | [`oneshot`]                                   | `oneshot`      | Send one value from one sender to one receiver.                                                               |
@@ -146,6 +147,8 @@ pub mod mutex;
 pub mod once;
 #[cfg(feature = "oneshot")]
 pub mod oneshot;
+#[cfg(feature = "phaser")]
+pub mod phaser;
 #[cfg(feature = "pool")]
 pub mod pool;
 #[cfg(feature = "rwlock")]