1 files changed, 72 insertions, 0 deletions
diff --git a/third_party/rust/tokio/src/time/error.rs b/third_party/rust/tokio/src/time/error.rs
new file mode 100644
index 0000000000..0667b97ac1
--- /dev/null
+++ b/third_party/rust/tokio/src/time/error.rs
@@ -0,0 +1,72 @@
+use self::Kind::*;
+use std::error;
+use std::fmt;
+
+/// Errors encountered by the timer implementation.
+///
+/// Currently, there are two different errors that can occur:
+///
+/// * `shutdown` occurs when a timer operation is attempted, but the timer
+///   instance has been dropped. In this case, the operation will never be able
+///   to complete and the `shutdown` error is returned. This is a permanent
+///   error, i.e., once this error is observed, timer operations will never
+///   succeed in the future.
+///
+/// * `at_capacity` occurs when a timer operation is attempted, but the timer
+///   instance is currently handling its maximum number of outstanding delays.
+///   In this case, the operation is not able to be performed at the current
+///   moment, and `at_capacity` is returned. This is a transient error, i.e., at
+///   some point in the future, if the operation is attempted again, it might
+///   succeed. Callers that observe this error should attempt to [shed load]. One
+///   way to do this would be dropping the future that issued the timer operation.
+///
+/// [shed load]: https://en.wikipedia.org/wiki/Load_Shedding
+#[derive(Debug)]
+pub struct Error(Kind);
+
+#[derive(Debug)]
+enum Kind {
+    Shutdown,
+    AtCapacity,
+}
+
+impl Error {
+    /// Creates an error representing a shutdown timer.
+    pub fn shutdown() -> Error {
+        Error(Shutdown)
+    }
+
+    /// Returns `true` if the error was caused by the timer being shutdown.
+    pub fn is_shutdown(&self) -> bool {
+        match self.0 {
+            Kind::Shutdown => true,
+            _ => false,
+        }
+    }
+
+    /// Creates an error representing a timer at capacity.
+    pub fn at_capacity() -> Error {
+        Error(AtCapacity)
+    }
+
+    /// Returns `true` if the error was caused by the timer being at capacity.
+    pub fn is_at_capacity(&self) -> bool {
+        match self.0 {
+            Kind::AtCapacity => true,
+            _ => false,
+        }
+    }
+}
+
+impl error::Error for Error {}
+
+impl fmt::Display for Error {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use self::Kind::*;
+        let descr = match self.0 {
+            Shutdown => "the timer is shutdown, must be called from the context of Tokio runtime",
+            AtCapacity => "timer is at capacity and cannot create a new entry",
+        };
+        write!(fmt, "{}", descr)
+    }
+}