Vendor things

third-party/vendor/gpu-alloc/src/util.rs

@@ -0,0 +1,44 @@
+use alloc::sync::Arc;
+
+/// Guarantees uniqueness only if `Weak` pointers are never created
+/// from this `Arc` or clones.
+pub(crate) fn is_arc_unique<M>(arc: &mut Arc<M>) -> bool {
+    let strong_count = Arc::strong_count(&*arc);
+    debug_assert_ne!(strong_count, 0, "This Arc should exist");
+
+    debug_assert!(
+        strong_count > 1 || Arc::get_mut(arc).is_some(),
+        "`Weak` pointer exists"
+    );
+
+    strong_count == 1
+}
+
+/// Can be used instead of `Arc::try_unwrap(arc).unwrap()`
+/// when it is guaranteed to succeed.
+pub(crate) unsafe fn arc_unwrap<M>(mut arc: Arc<M>) -> M {
+    use core::{mem::ManuallyDrop, ptr::read};
+    debug_assert!(is_arc_unique(&mut arc));
+
+    // Get raw pointer to inner value.
+    let raw = Arc::into_raw(arc);
+
+    // As `Arc` is unique and no Weak pointers exist
+    // it won't be dereferenced elsewhere.
+    let inner = read(raw);
+
+    // Cast to `ManuallyDrop` which guarantees to have same layout
+    // and will skip dropping.
+    drop(Arc::from_raw(raw as *const ManuallyDrop<M>));
+    inner
+}
+
+/// Can be used instead of `Arc::try_unwrap`
+/// only if `Weak` pointers are never created from this `Arc` or clones.
+pub(crate) unsafe fn try_arc_unwrap<M>(mut arc: Arc<M>) -> Option<M> {
+    if is_arc_unique(&mut arc) {
+        Some(arc_unwrap(arc))
+    } else {
+        None
+    }
+}