1 files changed, 32 insertions, 0 deletions
diff --git a/tokio/src/util/slab/generation.rs b/tokio/src/util/slab/generation.rs
new file mode 100644
index 00000000..4b16b2ca
--- /dev/null
+++ b/tokio/src/util/slab/generation.rs
@@ -0,0 +1,32 @@
+use crate::util::bit;
+use crate::util::slab::Address;
+
+/// An mutation identifier for a slot in the slab. The generation helps prevent
+/// accessing an entry with an outdated token.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Ord, PartialOrd)]
+pub(crate) struct Generation(usize);
+
+impl Generation {
+    pub(crate) const WIDTH: u32 = Address::GENERATION_WIDTH;
+
+    pub(super) const MAX: usize = bit::mask_for(Address::GENERATION_WIDTH);
+
+    /// Create a new generation
+    ///
+    /// # Panics
+    ///
+    /// Panics if `value` is greater than max generation.
+    pub(crate) fn new(value: usize) -> Generation {
+        assert!(value <= Self::MAX);
+        Generation(value)
+    }
+
+    /// Returns the next generation value
+    pub(crate) fn next(self) -> Generation {
+        Generation((self.0 + 1) & Self::MAX)
+    }
+
+    pub(crate) fn to_usize(self) -> usize {
+        self.0
+    }
+}