1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154

//! A minimal naive timer for embedded (no_std) platforms.
//!
//! # Example: single thread
//! ```
//! use alloc::sync::Arc;
//! use core::time::Duration;
//! use core::sync::atomic::{AtomicBool, Ordering};
//! use naive_timer::Timer;
//! extern crate alloc;
//!
//! let mut timer = Timer::default();
//! let event = Arc::new(AtomicBool::new(false));
//!
//! timer.add(Duration::from_secs(1), {
//!     let event = event.clone();
//!     move |now| event.store(true, Ordering::SeqCst)
//! });
//!
//! timer.expire(Duration::from_millis(999));
//! assert_eq!(event.load(Ordering::SeqCst), false);
//! assert_eq!(timer.next(), Some(Duration::from_secs(1)));
//!
//! timer.expire(Duration::from_millis(1000));
//! assert_eq!(event.load(Ordering::SeqCst), true);
//! assert_eq!(timer.next(), None);
//! ```
//!
//! # Example: ticks and wakeup
//! ```
//! use alloc::sync::Arc;
//! use core::time::Duration;
//! use core::sync::atomic::{AtomicU64, Ordering};
//! use std::time::{SystemTime, UNIX_EPOCH};
//! use naive_timer::Timer;
//! extern crate alloc;
//!
//! /// Get current time in `Duration`.
//! fn now() -> Duration {
//!     SystemTime::now().duration_since(UNIX_EPOCH).unwrap()
//! }
//!
//! let mut timer = Timer::default();
//!
//! // add timer to wake me up
//! let thread = std::thread::current();
//! timer.add(now() + Duration::from_millis(25), move |_| thread.unpark());
//!
//! // generate ticks (5 times per 10ms)
//! // spawn a thread to emulate timer interrupt
//! let handle = std::thread::spawn(move || {
//!     for _ in 0..5 {
//!         std::thread::sleep(Duration::from_millis(10));
//!         timer.expire(now());
//!     }
//! });
//!
//! // wait for wakeup
//! let t0 = now();
//! std::thread::park();
//! let sleep_time = now() - t0;
//! assert!(sleep_time > Duration::from_millis(30));
//! assert!(sleep_time < Duration::from_millis(40));
//!
//! // join thread
//! handle.join().unwrap();
//! ```
//!
//! # Limitations
//!
//! For simplicity, **timer cancellation** is not supported.
//!
//! The callback function should check the current time `now` and its own information,
//! to decide whether it is still a valid event.

#![no_std]
#![deny(missing_docs)]
#![deny(warnings)]

use alloc::boxed::Box;
use alloc::collections::BinaryHeap;
use core::cmp::Ordering;
use core::time::Duration;

extern crate alloc;

/// A naive timer.
#[derive(Default)]
pub struct Timer {
    events: BinaryHeap<Event>,
}

/// The type of callback function.
type Callback = Box<dyn FnOnce(Duration) + Send + Sync + 'static>;

impl Timer {
    /// Add a timer.
    ///
    /// The `callback` will be called on timer expired after `deadline`.
    pub fn add(
        &mut self,
        deadline: Duration,
        callback: impl FnOnce(Duration) + Send + Sync + 'static,
    ) {
        let event = Event {
            deadline,
            callback: Box::new(callback),
        };
        self.events.push(event);
    }

    /// Expire timers.
    ///
    /// Given the current time `now`, trigger and remove all expired timers.
    pub fn expire(&mut self, now: Duration) {
        while let Some(t) = self.events.peek() {
            if t.deadline > now {
                break;
            }
            let event = self.events.pop().unwrap();
            (event.callback)(now);
        }
    }

    /// Get next timer.
    pub fn next(&self) -> Option<Duration> {
        self.events.peek().map(|e| e.deadline)
    }
}

struct Event {
    deadline: Duration,
    callback: Callback,
}

impl PartialEq for Event {
    fn eq(&self, other: &Self) -> bool {
        self.deadline.eq(&other.deadline)
    }
}

impl Eq for Event {}

// BinaryHeap is a max-heap. So we need to reverse the order.
impl PartialOrd for Event {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        other.deadline.partial_cmp(&self.deadline)
    }
}

impl Ord for Event {
    fn cmp(&self, other: &Event) -> Ordering {
        other.deadline.cmp(&self.deadline)
    }
}