Add Forever

embassy/src/util/forever.rs

@@ -0,0 +1,33 @@
+use core::cell::UnsafeCell;
+use core::mem::MaybeUninit;
+use core::sync::atomic::{AtomicBool, Ordering};
+
+pub struct Forever<T> {
+    used: AtomicBool,
+    t: UnsafeCell<MaybeUninit<T>>,
+}
+
+unsafe impl<T> Send for Forever<T> {}
+unsafe impl<T> Sync for Forever<T> {}
+
+impl<T> Forever<T> {
+    pub const fn new() -> Self {
+        Self {
+            used: AtomicBool::new(false),
+            t: UnsafeCell::new(MaybeUninit::uninit()),
+        }
+    }
+
+    pub fn put(&self, val: T) -> &'static mut T {
+        if self.used.compare_and_swap(false, true, Ordering::SeqCst) {
+            panic!("Forever.put() called multiple times");
+        }
+
+        unsafe {
+            let p = self.t.get();
+            let p = (&mut *p).as_mut_ptr();
+            p.write(val);
+            &mut *p
+        }
+    }
+}

embassy/src/util/mod.rs

@@ -10,6 +10,8 @@ mod waker_store;
 pub use waker_store::*;
 mod drop_bomb;
 pub use drop_bomb::*;
+mod forever;
+pub use forever::*;
 
 use defmt::{debug, error, info, intern, trace, warn};