From 25dcb1fab5b18dbb9247a5424171bf45de1d1473 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Tue, 12 Sep 2017 22:54:13 -0700
Subject: [PATCH] Add {Interval,Timeout}::poll_at

Some contexts, like EC2, have `Instant::now` as a relatively expensive function
to call. To help amortize the cost of this function this commit exposes a new
function on `Interval` and `Timeout` to pass in the assumed current time.
---
 src/reactor/interval.rs | 31 +++++++++++++++++++++++--------
 src/reactor/timeout.rs  | 31 +++++++++++++++++++++++--------
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/src/reactor/interval.rs b/src/reactor/interval.rs
index 3859e4aed..bf766b9a7 100644
--- a/src/reactor/interval.rs
+++ b/src/reactor/interval.rs
@@ -55,15 +55,20 @@ impl Interval {
             handle: handle.remote().clone(),
         })
     }
-}
 
-impl Stream for Interval {
-    type Item = ();
-    type Error = io::Error;
-
-    fn poll(&mut self) -> Poll<Option<()>, io::Error> {
-        // TODO: is this fast enough?
-        let now = Instant::now();
+    /// Polls this `Interval` instance to see if it's elapsed, assuming the
+    /// current time is specified by `now`.
+    ///
+    /// The `Future::poll` implementation for `Interval` will call `Instant::now`
+    /// each time it's invoked, but in some contexts this can be a costly
+    /// operation. This method is provided to amortize the cost by avoiding
+    /// usage of `Instant::now`, assuming that it's been called elsewhere.
+    ///
+    /// This function takes the assumed current time as the first parameter and
+    /// otherwise functions as this future's `poll` function. This will block a
+    /// task if one isn't already blocked or update a previous one if already
+    /// blocked.
+    pub fn poll_at(&mut self, now: Instant) -> Poll<Option<()>, io::Error> {
         if self.next <= now {
             self.next = next_interval(self.next, now, self.interval);
             self.token.reset_timeout(self.next, &self.handle);
@@ -75,6 +80,16 @@ impl Stream for Interval {
     }
 }
 
+impl Stream for Interval {
+    type Item = ();
+    type Error = io::Error;
+
+    fn poll(&mut self) -> Poll<Option<()>, io::Error> {
+        // TODO: is this fast enough?
+        self.poll_at(Instant::now())
+    }
+}
+
 impl Drop for Interval {
     fn drop(&mut self) {
         self.token.cancel_timeout(&self.handle);
diff --git a/src/reactor/timeout.rs b/src/reactor/timeout.rs
index b67ab38ed..8f0b354c9 100644
--- a/src/reactor/timeout.rs
+++ b/src/reactor/timeout.rs
@@ -64,15 +64,20 @@ impl Timeout {
         self.when = at;
         self.token.reset_timeout(self.when, &self.handle);
     }
-}
 
-impl Future for Timeout {
-    type Item = ();
-    type Error = io::Error;
-
-    fn poll(&mut self) -> Poll<(), io::Error> {
-        // TODO: is this fast enough?
-        let now = Instant::now();
+    /// Polls this `Timeout` instance to see if it's elapsed, assuming the
+    /// current time is specified by `now`.
+    ///
+    /// The `Future::poll` implementation for `Timeout` will call `Instant::now`
+    /// each time it's invoked, but in some contexts this can be a costly
+    /// operation. This method is provided to amortize the cost by avoiding
+    /// usage of `Instant::now`, assuming that it's been called elsewhere.
+    ///
+    /// This function takes the assumed current time as the first parameter and
+    /// otherwise functions as this future's `poll` function. This will block a
+    /// task if one isn't already blocked or update a previous one if already
+    /// blocked.
+    pub fn poll_at(&mut self, now: Instant) -> Poll<(), io::Error> {
         if self.when <= now {
             Ok(Async::Ready(()))
         } else {
@@ -82,6 +87,16 @@ impl Future for Timeout {
     }
 }
 
+impl Future for Timeout {
+    type Item = ();
+    type Error = io::Error;
+
+    fn poll(&mut self) -> Poll<(), io::Error> {
+        // TODO: is this fast enough?
+        self.poll_at(Instant::now())
+    }
+}
+
 impl Drop for Timeout {
     fn drop(&mut self) {
         self.token.cancel_timeout(&self.handle);