executor: add "task metadata" concept, make name a task metadata.

.github/ci/test.sh

@@ -12,7 +12,7 @@ export CARGO_TARGET_DIR=/ci/cache/target
 # used when pointing stm32-metapac to a CI-built one.
 export CARGO_NET_GIT_FETCH_WITH_CLI=true
 
-cargo test --manifest-path ./embassy-executor/Cargo.toml
+cargo test --manifest-path ./embassy-executor/Cargo.toml --features metadata-name
 cargo test --manifest-path ./embassy-futures/Cargo.toml
 cargo test --manifest-path ./embassy-sync/Cargo.toml
 cargo test --manifest-path ./embassy-embedded-hal/Cargo.toml

ci.sh

@@ -31,6 +31,7 @@ cargo batch \
     --- build --release --manifest-path embassy-executor/Cargo.toml --target thumbv6m-none-eabi --features defmt \
     --- build --release --manifest-path embassy-executor/Cargo.toml --target thumbv6m-none-eabi --features defmt,arch-cortex-m,executor-thread,executor-interrupt \
     --- build --release --manifest-path embassy-executor/Cargo.toml --target thumbv7em-none-eabi --features arch-cortex-m \
+    --- build --release --manifest-path embassy-executor/Cargo.toml --target thumbv7em-none-eabi --features arch-cortex-m,metadata-name \
     --- build --release --manifest-path embassy-executor/Cargo.toml --target thumbv7em-none-eabi --features arch-cortex-m,trace \
     --- build --release --manifest-path embassy-executor/Cargo.toml --target thumbv7em-none-eabi --features arch-cortex-m,rtos-trace \
     --- build --release --manifest-path embassy-executor/Cargo.toml --target thumbv7em-none-eabi --features arch-cortex-m,trace,rtos-trace \

embassy-executor/Cargo.toml

@@ -109,6 +109,11 @@ arch-avr = ["_arch", "dep:portable-atomic", "dep:avr-device"]
 ## spin (architecture agnostic; never sleeps)
 arch-spin = ["_arch"]
 
+#! ### Metadata
+
+## Enable the `name` field in task metadata.
+metadata-name = []
+
 #! ### Executor
 
 ## Enable the thread-mode executor (using WFE/SEV in Cortex-M, WFI in other embedded archs)
@@ -118,5 +123,5 @@ executor-interrupt = []
 ## Enable tracing hooks
 trace = ["_any_trace"]
 ## Enable support for rtos-trace framework
-rtos-trace = ["dep:rtos-trace", "_any_trace", "dep:embassy-time-driver"]
+rtos-trace = ["_any_trace", "metadata-name", "dep:rtos-trace", "dep:embassy-time-driver"]
 _any_trace = []

embassy-executor/src/lib.rs

@@ -54,6 +54,9 @@ pub mod raw;
 mod spawner;
 pub use spawner::*;
 
+mod metadata;
+pub use metadata::*;
+
 /// Implementation details for embassy macros.
 /// Do not use. Used for macros and HALs only. Not covered by semver guarantees.
 #[doc(hidden)]

embassy-executor/src/metadata.rs

@@ -1 +1,55 @@
-pub struct Metadata {}
+#[cfg(feature = "metadata-name")]
+use core::cell::Cell;
+use core::future::{poll_fn, Future};
+use core::task::Poll;
+
+#[cfg(feature = "metadata-name")]
+use critical_section::Mutex;
+
+use crate::raw;
+
+/// Metadata associated with a task.
+pub struct Metadata {
+    #[cfg(feature = "metadata-name")]
+    name: Mutex<Cell<Option<&'static str>>>,
+}
+
+impl Metadata {
+    pub(crate) const fn new() -> Self {
+        Self {
+            #[cfg(feature = "metadata-name")]
+            name: Mutex::new(Cell::new(None)),
+        }
+    }
+
+    pub(crate) fn reset(&self) {
+        #[cfg(feature = "metadata-name")]
+        critical_section::with(|cs| self.name.borrow(cs).set(None));
+    }
+
+    /// Get the metadata for the current task.
+    ///
+    /// You can use this to read or modify the current task's metadata.
+    ///
+    /// This function is `async` just to get access to the current async
+    /// context. It returns instantly, it does not block/yield.
+    pub fn for_current_task() -> impl Future<Output = &'static Self> {
+        poll_fn(|cx| Poll::Ready(raw::task_from_waker(cx.waker()).metadata()))
+    }
+
+    /// Get this task's name
+    ///
+    /// NOTE: this takes a critical section.
+    #[cfg(feature = "metadata-name")]
+    pub fn name(&self) -> Option<&'static str> {
+        critical_section::with(|cs| self.name.borrow(cs).get())
+    }
+
+    /// Set this task's name
+    ///
+    /// NOTE: this takes a critical section.
+    #[cfg(feature = "metadata-name")]
+    pub fn set_name(&self, name: &'static str) {
+        critical_section::with(|cs| self.name.borrow(cs).set(Some(name)))
+    }
+}

embassy-executor/src/raw/mod.rs

@@ -41,6 +41,7 @@ use self::state::State;
 use self::util::{SyncUnsafeCell, UninitCell};
 pub use self::waker::task_from_waker;
 use super::SpawnToken;
+use crate::Metadata;
 
 #[no_mangle]
 extern "Rust" fn __embassy_time_queue_item_from_waker(waker: &Waker) -> &'static mut TimerQueueItem {
@@ -94,8 +95,8 @@ pub(crate) struct TaskHeader {
 
     /// Integrated timer queue storage. This field should not be accessed outside of the timer queue.
     pub(crate) timer_queue_item: TimerQueueItem,
-    #[cfg(feature = "_any_trace")]
-    pub(crate) name: Option<&'static str>,
+    pub(crate) metadata: Metadata,
+
     #[cfg(feature = "rtos-trace")]
     all_tasks_next: AtomicPtr<TaskHeader>,
 }
@@ -127,6 +128,10 @@ impl TaskRef {
         unsafe { self.ptr.as_ref() }
     }
 
+    pub(crate) fn metadata(self) -> &'static Metadata {
+        unsafe { &self.ptr.as_ref().metadata }
+    }
+
     /// Returns a reference to the executor that the task is currently running on.
     pub unsafe fn executor(self) -> Option<&'static Executor> {
         let executor = self.header().executor.load(Ordering::Relaxed);
@@ -193,8 +198,7 @@ impl<F: Future + 'static> TaskStorage<F> {
                 poll_fn: SyncUnsafeCell::new(None),
 
                 timer_queue_item: TimerQueueItem::new(),
-                #[cfg(feature = "_any_trace")]
-                name: None,
+                metadata: Metadata::new(),
                 #[cfg(feature = "rtos-trace")]
                 all_tasks_next: AtomicPtr::new(core::ptr::null_mut()),
             },
@@ -281,6 +285,7 @@ impl<F: Future + 'static> AvailableTask<F> {
 
     fn initialize_impl<S>(self, future: impl FnOnce() -> F) -> SpawnToken<S> {
         unsafe {
+            self.task.raw.metadata.reset();
             self.task.raw.poll_fn.set(Some(TaskStorage::<F>::poll));
             self.task.future.write_in_place(future);
 

embassy-executor/src/raw/trace.rs

@@ -168,32 +168,6 @@ impl TaskTracker {
     }
 }
 
-/// Extension trait for `TaskRef` that provides tracing functionality.
-///
-/// This trait is only available when the `trace` feature is enabled.
-/// It extends `TaskRef` with methods for accessing and modifying task identifiers
-/// and names, which are useful for debugging, logging, and performance analysis.
-pub trait TaskRefTrace {
-    /// Get the name for a task
-    fn name(&self) -> Option<&'static str>;
-
-    /// Set the name for a task
-    fn set_name(&self, name: Option<&'static str>);
-}
-
-impl TaskRefTrace for TaskRef {
-    fn name(&self) -> Option<&'static str> {
-        self.header().name
-    }
-
-    fn set_name(&self, name: Option<&'static str>) {
-        unsafe {
-            let header_ptr = self.ptr.as_ptr() as *mut TaskHeader;
-            (*header_ptr).name = name;
-        }
-    }
-}
-
 #[cfg(feature = "trace")]
 extern "Rust" {
     /// This callback is called when the executor begins polling. This will always
@@ -383,9 +357,8 @@ where
 impl rtos_trace::RtosTraceOSCallbacks for crate::raw::SyncExecutor {
     fn task_list() {
         with_all_active_tasks(|task| {
-            let name = task.name().unwrap_or("unnamed task\0");
             let info = rtos_trace::TaskInfo {
-                name,
+                name: task.metadata().name().unwrap_or("unnamed task\0"),
                 priority: 0,
                 stack_base: 0,
                 stack_size: 0,

embassy-executor/src/spawner.rs

@@ -5,8 +5,7 @@ use core::sync::atomic::Ordering;
 use core::task::Poll;
 
 use super::raw;
-#[cfg(feature = "trace")]
-use crate::raw::trace::TaskRefTrace;
+use crate::Metadata;
 
 /// Token to spawn a newly-created task in an executor.
 ///
@@ -36,6 +35,14 @@ impl<S> SpawnToken<S> {
         }
     }
 
+    /// Return a SpawnToken that represents a failed spawn.
+    pub fn new_failed() -> Self {
+        Self {
+            raw_task: None,
+            phantom: PhantomData,
+        }
+    }
+
     /// Returns the task ID if available, otherwise 0
     /// This can be used in combination with rtos-trace to match task names with IDs
     pub fn id(&self) -> u32 {
@@ -45,12 +52,10 @@ impl<S> SpawnToken<S> {
         }
     }
 
-    /// Return a SpawnToken that represents a failed spawn.
-    pub fn new_failed() -> Self {
-        Self {
-            raw_task: None,
-            phantom: PhantomData,
-        }
+    /// Get the metadata for this task. You can use this to set metadata fields
+    /// prior to spawning it.
+    pub fn metadata(&self) -> &Metadata {
+        self.raw_task.unwrap().metadata()
     }
 }
 
@@ -198,51 +203,6 @@ impl Spawner {
     }
 }
 
-/// Extension trait adding tracing capabilities to the Spawner
-///
-/// This trait provides an additional method to spawn tasks with an associated name,
-/// which can be useful for debugging and tracing purposes.
-pub trait SpawnerTraceExt {
-    /// Spawns a new task with a specified name.
-    ///
-    /// # Arguments
-    /// * `name` - Static string name to associate with the task
-    /// * `token` - Token representing the task to spawn
-    ///
-    /// # Returns
-    /// Result indicating whether the spawn was successful
-    fn spawn_named<S>(&self, name: &'static str, token: SpawnToken<S>) -> Result<(), SpawnError>;
-}
-
-/// Implementation of the SpawnerTraceExt trait for Spawner when trace is enabled
-#[cfg(feature = "trace")]
-impl SpawnerTraceExt for Spawner {
-    fn spawn_named<S>(&self, name: &'static str, token: SpawnToken<S>) -> Result<(), SpawnError> {
-        let task = token.raw_task;
-        core::mem::forget(token);
-
-        match task {
-            Some(task) => {
-                // Set the name when trace is enabled
-                task.set_name(Some(name));
-
-                unsafe { self.executor.spawn(task) };
-                Ok(())
-            }
-            None => Err(SpawnError::Busy),
-        }
-    }
-}
-
-/// Implementation of the SpawnerTraceExt trait for Spawner when trace is disabled
-#[cfg(not(feature = "trace"))]
-impl SpawnerTraceExt for Spawner {
-    fn spawn_named<S>(&self, _name: &'static str, token: SpawnToken<S>) -> Result<(), SpawnError> {
-        // When trace is disabled, just forward to regular spawn and ignore the name
-        self.spawn(token)
-    }
-}
-
 /// Handle to spawn tasks into an executor from any thread.
 ///
 /// This Spawner can be used from any thread (it is Send), but it can

embassy-executor/tests/test.rs

@@ -326,3 +326,34 @@ fn recursive_task() {
         spawner.spawn(task1());
     }
 }
+
+#[cfg(feature = "metadata-name")]
+#[test]
+fn task_metadata() {
+    #[task]
+    async fn task1(expected_name: Option<&'static str>) {
+        use embassy_executor::Metadata;
+        assert_eq!(Metadata::for_current_task().await.name(), expected_name);
+    }
+
+    // check no task name
+    let (executor, _) = setup();
+    executor.spawner().spawn(task1(None)).unwrap();
+    unsafe { executor.poll() };
+
+    // check setting task name
+    let token = task1(Some("foo"));
+    token.metadata().set_name("foo");
+    executor.spawner().spawn(token).unwrap();
+    unsafe { executor.poll() };
+
+    let token = task1(Some("bar"));
+    token.metadata().set_name("bar");
+    executor.spawner().spawn(token).unwrap();
+    unsafe { executor.poll() };
+
+    // check name is cleared if the task pool slot is recycled.
+    let (executor, _) = setup();
+    executor.spawner().spawn(task1(None)).unwrap();
+    unsafe { executor.poll() };
+}