Make PenderContext opaque

embassy-executor/src/arch/cortex_m.rs

@@ -36,6 +36,7 @@ unsafe fn nvic_pend(irq: u16) {
 #[export_name = "__pender"]
 fn __pender(context: PenderContext) {
     unsafe {
+        let context: usize = core::mem::transmute(context);
         // Safety: `context` is either `usize::MAX` created by `Executor::run`, or a valid interrupt
         // request number given to `InterruptExecutor::start`.
         if context as usize == usize::MAX {
@@ -56,6 +57,7 @@ fn __pender(_context: PenderContext) {
 #[export_name = "__pender"]
 fn __pender(context: PenderContext) {
     unsafe {
+        let context: usize = core::mem::transmute(context);
         // Safety: `context` is the same value we passed to `InterruptExecutor::start`, which must
         // be a valid interrupt request number.
         nvic_pend(context as u16)
@@ -78,7 +80,7 @@ mod thread {
 
     impl ThreadContext for Context {
         fn context(&self) -> PenderContext {
-            usize::MAX
+            unsafe { core::mem::transmute(usize::MAX) }
         }
 
         fn wait(&mut self) {
@@ -106,7 +108,7 @@ mod interrupt {
         T: InterruptNumber,
     {
         fn context(&self) -> PenderContext {
-            self.number() as usize
+            unsafe { core::mem::transmute(self.number() as usize) }
         }
 
         fn enable(&self) {

embassy-executor/src/arch/riscv32.rs

@@ -28,7 +28,7 @@ mod thread {
 
     impl ThreadContext for Context {
         fn context(&self) -> PenderContext {
-            0
+            unsafe { core::mem::transmute(0) }
         }
 
         fn wait(&mut self) {

embassy-executor/src/arch/std.rs

@@ -29,7 +29,7 @@ mod thread {
 
     impl ThreadContext for Context {
         fn context(&self) -> PenderContext {
-            self.signaler as *const _ as usize
+            unsafe { core::mem::transmute(self.signaler) }
         }
 
         fn wait(&mut self) {

embassy-executor/src/arch/wasm.rs

@@ -49,7 +49,7 @@ mod thread {
         pub fn new() -> Self {
             let ctx = &*Box::leak(Box::new(WasmContext::new()));
             Self {
-                inner: raw::Executor::new(ctx as *const _ as usize),
+                inner: raw::Executor::new(unsafe { core::mem::transmute(ctx) }),
                 ctx,
                 not_send: PhantomData,
             }

embassy-executor/src/arch/xtensa.rs

@@ -26,7 +26,7 @@ mod thread {
 
     impl ThreadContext for Context {
         fn context(&self) -> PenderContext {
-            0
+            unsafe { core::mem::transmute(0) }
         }
 
         fn wait(&mut self) {

embassy-executor/src/raw/mod.rs

@@ -292,10 +292,29 @@ impl<F: Future + 'static, const N: usize> TaskPool<F, N> {
 }
 
 /// Context given to the thread-mode executor's pender.
-pub type PenderContext = usize;
-
+#[repr(transparent)]
 #[derive(Clone, Copy)]
-pub(crate) struct Pender(PenderContext);
+pub struct PenderContext(usize);
+
+/// Platform/architecture-specific action executed when an executor has pending work.
+///
+/// When a task within an executor is woken, the `Pender` is called. This does a
+/// platform/architecture-specific action to signal there is pending work in the executor.
+/// When this happens, you must arrange for [`Executor::poll`] to be called.
+///
+/// You can think of it as a waker, but for the whole executor.
+///
+/// Platform/architecture implementations must provide a function that can be referred to as:
+///
+/// ```rust
+/// use embassy_executor::raw::PenderContext;
+///
+/// extern "Rust" {
+///     fn __pender(context: PenderContext);
+/// }
+/// ```
+#[derive(Clone, Copy)]
+pub struct Pender(PenderContext);
 
 unsafe impl Send for Pender {}
 unsafe impl Sync for Pender {}