1 files changed, 58 insertions, 0 deletions
diff --git a/third_party/rust/tokio/src/util/slab/stack.rs b/third_party/rust/tokio/src/util/slab/stack.rs
new file mode 100644
index 0000000000..0ae0d71006
--- /dev/null
+++ b/third_party/rust/tokio/src/util/slab/stack.rs
@@ -0,0 +1,58 @@
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::util::slab::Address;
+
+use std::fmt;
+use std::sync::atomic::Ordering;
+use std::usize;
+
+pub(super) struct TransferStack {
+    head: AtomicUsize,
+}
+
+impl TransferStack {
+    pub(super) fn new() -> Self {
+        Self {
+            head: AtomicUsize::new(Address::NULL),
+        }
+    }
+
+    pub(super) fn pop_all(&self) -> Option<usize> {
+        let val = self.head.swap(Address::NULL, Ordering::Acquire);
+
+        if val == Address::NULL {
+            None
+        } else {
+            Some(val)
+        }
+    }
+
+    pub(super) fn push(&self, value: usize, before: impl Fn(usize)) {
+        let mut next = self.head.load(Ordering::Relaxed);
+
+        loop {
+            before(next);
+
+            match self
+                .head
+                .compare_exchange(next, value, Ordering::AcqRel, Ordering::Acquire)
+            {
+                // lost the race!
+                Err(actual) => next = actual,
+                Ok(_) => return,
+            }
+        }
+    }
+}
+
+impl fmt::Debug for TransferStack {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Loom likes to dump all its internal state in `fmt::Debug` impls, so
+        // we override this to just print the current value in tests.
+        f.debug_struct("TransferStack")
+            .field(
+                "head",
+                &format_args!("{:#x}", self.head.load(Ordering::Relaxed)),
+            )
+            .finish()
+    }
+}