util/timer: introduce steady timer (tikv#4060)

Steady timer is used to create futures that is notified after a given
duration. It's called steady because it won't be affected by the time
adjustment. This is important for raftstore as the lease mechanism is
based on a steady time.

Cargo.toml

@@ -85,6 +85,7 @@ futures-cpupool = "0.1"
 tokio = "0.1"
 tokio-core = "0.1"
 tokio-timer = "0.2"
+tokio-executor = "0.1"
 serde = "1.0"
 serde_json = "1.0"
 serde_derive = "1.0"

src/lib.rs

@@ -106,6 +106,7 @@ extern crate time;
 extern crate tipb;
 extern crate tokio;
 extern crate tokio_core;
+extern crate tokio_executor;
 extern crate tokio_timer;
 #[cfg(test)]
 extern crate toml;

src/util/time.rs

@@ -295,7 +295,7 @@ impl Instant {
         }
     }
 
-    fn elapsed_duration(later: Timespec, earlier: Timespec) -> Duration {
+    pub fn elapsed_duration(later: Timespec, earlier: Timespec) -> Duration {
         if later >= earlier {
             (later - earlier).to_std().unwrap()
         } else {

src/util/timer.rs

@@ -13,11 +13,13 @@
 
 use std::cmp::{Ord, Ordering, Reverse};
 use std::collections::BinaryHeap;
-use std::sync::mpsc;
+use std::sync::{mpsc, Arc};
 use std::thread::Builder;
 use std::time::Duration;
-use tokio_timer::{self, timer::Handle};
-use util::time::Instant;
+use time::Timespec;
+use tokio_executor::park::ParkThread;
+use tokio_timer::{self, clock::Clock, clock::Now, timer::Handle, Delay};
+use util::time::{monotonic_raw_now, Instant};
 
 pub struct Timer<T> {
     pending: BinaryHeap<Reverse<TimeoutTask<T>>>,
@@ -107,6 +109,107 @@ fn start_global_timer() -> Handle {
     rx.recv().unwrap()
 }
 
+/// A struct that marks the *zero* time.
+///
+/// A *zero* time can be any time, as what it represents is `Instant`,
+/// which is Opaque.
+struct TimeZero {
+    /// An arbitrary time used as the zero time.
+    ///
+    /// Note that `zero` doesn't have to be related to `steady_time_point`, as what's
+    /// observed here is elapsed time instead of time point.
+    zero: ::std::time::Instant,
+    /// A base time point.
+    ///
+    /// The source of time point should grow steady.
+    steady_time_point: Timespec,
+}
+
+/// A clock that produces time in a steady speed.
+///
+/// Time produced by the clock is not affected by clock jump or time adjustment.
+/// Internally it uses CLOCK_MONOTONIC_RAW to get a steady time source.
+///
+/// `Instant`s produced by this clock can't be compared or used to calculate elapse
+/// unless they are produced using the same zero time.
+#[derive(Clone)]
+pub struct SteadyClock {
+    zero: Arc<TimeZero>,
+}
+
+lazy_static! {
+    static ref STEADY_CLOCK: SteadyClock = SteadyClock {
+        zero: Arc::new(TimeZero {
+            zero: ::std::time::Instant::now(),
+            steady_time_point: monotonic_raw_now(),
+        }),
+    };
+}
+
+impl Default for SteadyClock {
+    #[inline]
+    fn default() -> SteadyClock {
+        STEADY_CLOCK.clone()
+    }
+}
+
+impl Now for SteadyClock {
+    #[inline]
+    fn now(&self) -> ::std::time::Instant {
+        let n = monotonic_raw_now();
+        let dur = Instant::elapsed_duration(n, self.zero.steady_time_point);
+        self.zero.zero + dur
+    }
+}
+
+/// A timer that creates steady delays.
+///
+/// Delay created by this timer will not be affected by time adjustment.
+#[derive(Clone)]
+pub struct SteadyTimer {
+    clock: SteadyClock,
+    handle: Handle,
+}
+
+impl SteadyTimer {
+    /// Creates a delay future that will be notified after the given duration.
+    pub fn delay(&self, dur: Duration) -> Delay {
+        self.handle.delay(self.clock.now() + dur)
+    }
+}
+
+lazy_static! {
+    static ref GLOBAL_STEADY_TIMER: SteadyTimer = start_global_steady_timer();
+}
+
+impl Default for SteadyTimer {
+    #[inline]
+    fn default() -> SteadyTimer {
+        GLOBAL_STEADY_TIMER.clone()
+    }
+}
+
+fn start_global_steady_timer() -> SteadyTimer {
+    let (tx, rx) = mpsc::channel();
+    let clock = SteadyClock::default();
+    let clock_ = clock.clone();
+    Builder::new()
+        .name(thd_name!("steady-timer"))
+        .spawn(move || {
+            let c = Clock::new_with_now(clock_);
+            let mut timer = tokio_timer::Timer::new_with_now(ParkThread::new(), c);
+            tx.send(timer.handle()).unwrap();
+            loop {
+                timer.turn(None).unwrap();
+            }
+        })
+        .unwrap();
+    SteadyTimer {
+        clock,
+        handle: rx.recv().unwrap(),
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -226,4 +329,13 @@ mod tests {
         delay.wait().unwrap();
         assert!(timer.elapsed() >= Duration::from_millis(100));
     }
+
+    #[test]
+    fn test_global_steady_timer() {
+        let t = SteadyTimer::default();
+        let timer = t.clock.now();
+        let delay = t.delay(Duration::from_millis(100));
+        delay.wait().unwrap();
+        assert!(timer.elapsed() >= Duration::from_millis(100));
+    }
 }