switch to instant+bool combo

tokio/src/runtime/time/entry.rs

@@ -298,19 +298,15 @@ pub(crate) struct TimerEntry {
     /// This is manipulated only under the inner mutex. TODO: Can we use loom
     /// cells for this?
     inner: StdUnsafeCell<TimerShared>,
-    /// Initial deadline for the timer. This is used to register on the first
+    /// Deadline for the timer. This is used to register on the first
     /// poll, as we can't register prior to being pinned.
-    deadline: Deadline,
+    deadline: Instant,
+    /// Whether the deadline has been registered.
+    registered: bool,
     /// Ensure the type is !Unpin
     _m: std::marker::PhantomPinned,
 }
 
-#[derive(Debug)]
-enum Deadline {
-    Unregistered(Instant),
-    Registered(Instant),
-}
-
 unsafe impl Send for TimerEntry {}
 unsafe impl Sync for TimerEntry {}
 
@@ -510,7 +506,8 @@ impl TimerEntry {
         Self {
             driver,
             inner: StdUnsafeCell::new(TimerShared::new()),
-            deadline: Deadline::Unregistered(deadline),
+            deadline,
+            registered: false,
             _m: std::marker::PhantomPinned,
         }
     }
@@ -520,15 +517,11 @@ impl TimerEntry {
     }
 
     pub(crate) fn deadline(&self) -> Instant {
-        match self.deadline {
-            Deadline::Unregistered(x) => x,
-            Deadline::Registered(x) => x,
-        }
+        self.deadline
     }
 
     pub(crate) fn is_elapsed(&self) -> bool {
-        !self.inner().state.might_be_registered()
-            && matches!(self.deadline, Deadline::Registered(_))
+        !self.inner().state.might_be_registered() && self.registered
     }
 
     /// Cancels and deregisters the timer. This operation is irreversible.
@@ -559,7 +552,8 @@ impl TimerEntry {
     }
 
     pub(crate) fn reset(mut self: Pin<&mut Self>, new_time: Instant) {
-        unsafe { self.as_mut().get_unchecked_mut() }.deadline = Deadline::Registered(new_time);
+        unsafe { self.as_mut().get_unchecked_mut() }.deadline = new_time;
+        unsafe { self.as_mut().get_unchecked_mut() }.registered = true;
 
         let tick = self.driver().time_source().deadline_to_tick(new_time);
 
@@ -581,7 +575,8 @@ impl TimerEntry {
             panic!("{}", crate::util::error::RUNTIME_SHUTTING_DOWN_ERROR);
         }
 
-        if let Deadline::Unregistered(deadline) = self.deadline {
+        if !self.registered {
+            let deadline = self.deadline;
             self.as_mut().reset(deadline);
         }