feat(phaser): add reusable phase coordination

CHANGELOG.md

@@ -45,6 +45,7 @@ This non-ASF release was not approved by the Apache Incubator PMC, is not an act
 * 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

@@ -71,6 +71,7 @@ Runnable examples live in the [`examples`](examples) workspace crate. They demon
 |                            | [`Barrier`](https://docs.rs/asyncband/*/asyncband/barrier/struct.Barrier.html)                 | `barrier`      | Synchronize a fixed number of participants at a reusable rendezvous.                                          |
 |                            | [`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`    | Dynamically register participants and wait until all have completed.                                          |
 |                            | [`Shutdown`](https://docs.rs/asyncband/*/asyncband/shutdown/struct.Shutdown.html)              | `shutdown`     | Request shutdown and wait until all completion guards are dropped.                                            |
 | Work coalescing            | [`Once`](https://docs.rs/asyncband/*/asyncband/once/struct.Once.html)                          | `once`         | Complete one asynchronous initialization; cancelled or panicked attempts may be retried.                       |

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

@@ -60,6 +60,7 @@ pub(crate) mod atomic_waker;
     feature = "latch",
     feature = "mpsc",
     feature = "mutex",
+    feature = "phaser",
     feature = "rwlock",
     feature = "semaphore",
     feature = "waitgroup",
@@ -87,6 +88,7 @@ pub(crate) mod value_cell;
     feature = "latch",
     feature = "mpsc",
     feature = "mutex",
+    feature = "phaser",
     feature = "rwlock",
     feature = "semaphore",
     feature = "waitgroup",
@@ -127,6 +129,7 @@ pub(crate) mod waitlist;
     feature = "mpsc",
     feature = "mutex",
     feature = "once",
+    feature = "phaser",
     feature = "rwlock",
     feature = "semaphore",
     feature = "waitgroup",
@@ -143,6 +146,7 @@ pub(crate) mod waker_batch;
     feature = "completion",
     feature = "latch",
     feature = "once",
+    feature = "phaser",
     feature = "waitgroup",
     feature = "watch",
 ))]

asyncband/src/lib.rs

@@ -63,6 +63,7 @@
 //! |                            | [`Barrier`](barrier::Barrier)                 | `barrier`      | Synchronize a fixed number of participants at a reusable rendezvous.                                          |
 //! |                            | [`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`    | Dynamically register participants and wait until all have completed.                                          |
 //! |                            | [`Shutdown`](shutdown::Shutdown)              | `shutdown`     | Request shutdown and wait until all completion guards are dropped.                                            |
 //! | Work coalescing            | [`Once`](once::Once)                          | `once`         | Complete one asynchronous initialization; cancelled or panicked attempts may be retried.                       |
@@ -145,6 +146,8 @@ 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")]