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
155
156
157
158
159
160
161
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

//! An event loop implementation that works in headless mode.


use glutin;
use servo::embedder_traits::EventLoopWaker;
use std::sync::{Arc, Condvar, Mutex};
use std::rc::Rc;
use std::cell::RefCell;
use std::time;

#[allow(dead_code)]
enum EventLoop {
    /// A real Glutin windowing event loop.
    Glutin(Option<glutin::EventsLoop>),
    /// A fake event loop which contains a signalling flag used to ensure
    /// that pending events get processed in a timely fashion, and a condition
    /// variable to allow waiting on that flag changing state.
    Headless(Arc<(Mutex<bool>, Condvar)>),
}

pub struct EventsLoop(EventLoop);

impl EventsLoop {
    // Ideally, we could use the winit event loop in both modes,
    // but on Linux, the event loop requires a X11 server.
    #[cfg(not(target_os = "linux"))]
    pub fn new(_headless: bool) -> Rc<RefCell<EventsLoop>> {
        Rc::new(RefCell::new(EventsLoop(EventLoop::Glutin(Some(glutin::EventsLoop::new())))))
    }
    #[cfg(target_os = "linux")]
    pub fn new(headless: bool) -> Rc<RefCell<EventsLoop>> {
        let events_loop = if headless {
            EventLoop::Headless(Arc::new((Mutex::new(false), Condvar::new())))
        } else {
            EventLoop::Glutin(Some(glutin::EventsLoop::new()))
        };
        Rc::new(RefCell::new(EventsLoop(events_loop)))
    }
}

impl EventsLoop {
    pub fn create_event_loop_waker(&self) -> Box<dyn EventLoopWaker> {
        match self.0 {
            EventLoop::Glutin(ref events_loop) => {
                let events_loop = events_loop
                    .as_ref()
                    .expect("Can't create waker for unavailable event loop.");
                Box::new(HeadedEventLoopWaker::new(&events_loop))
            },
            EventLoop::Headless(ref data) =>
                Box::new(HeadlessEventLoopWaker(data.clone())),
        }
    }
    pub fn as_winit(&self) -> &glutin::EventsLoop {
        match self.0 {
            EventLoop::Glutin(Some(ref event_loop)) => event_loop,
            EventLoop::Glutin(None) | EventLoop::Headless(..) =>
                panic!("Can't access winit event loop while using the fake headless event loop"),
        }
    }
    pub fn take(&mut self) -> Option<glutin::EventsLoop> {
        match self.0 {
            EventLoop::Glutin(ref mut event_loop) => event_loop.take(),
            EventLoop::Headless(..) => None,
        }
    }
    pub fn poll_events<F>(&mut self, callback: F) where F: FnMut(glutin::Event) {
        match self.0 {
            EventLoop::Glutin(Some(ref mut events_loop)) => events_loop.poll_events(callback),
            EventLoop::Glutin(None) => (),
            EventLoop::Headless(ref data) => {
                // This is subtle - the use of the event loop in App::run_loop
                // optionally calls run_forever, then always calls poll_events.
                // If our signalling flag is true before we call run_forever,
                // we don't want to reset it before poll_events is called or
                // we'll end up sleeping even though there are events waiting
                // to be handled. We compromise by only resetting the flag here
                // in poll_events, so that both poll_events and run_forever can
                // check it first and avoid sleeping unnecessarily.
                self.sleep(&data.0, &data.1);
                *data.0.lock().unwrap() = false;
            }
        }
    }
    pub fn run_forever<F>(&mut self, mut callback: F) where F: FnMut(glutin::Event) -> glutin::ControlFlow {
        match self.0 {
            EventLoop::Glutin(ref mut events_loop) => {
                let events_loop = events_loop
                    .as_mut()
                    .expect("Can't run an unavailable event loop.");
                events_loop.run_forever(callback);
            }
            EventLoop::Headless(ref data) => {
                let &(ref flag, ref condvar) = &**data;
                while { !*flag.lock().unwrap() } {
                    self.sleep(flag, condvar);
                    if callback(glutin::Event::Awakened) == glutin::ControlFlow::Break {
                        break;
                    }
                }
            }
        }
    }
    fn sleep(&self, lock: &Mutex<bool>, condvar: &Condvar) {
        // To avoid sleeping when we should be processing events, do two things:
        // * before sleeping, check whether our signalling flag has been set
        // * wait on a condition variable with a maximum timeout, to allow
        //   being woken up by any signals that occur while sleeping.
        let guard = lock.lock().unwrap();
        if *guard {
            return;
        }
        let _ = condvar.wait_timeout(
            guard, time::Duration::from_millis(5)
        ).unwrap();
    }
}

struct HeadedEventLoopWaker {
    proxy: Arc<glutin::EventsLoopProxy>,
}
impl HeadedEventLoopWaker {
    fn new(events_loop: &glutin::EventsLoop) -> HeadedEventLoopWaker {
        let proxy = Arc::new(events_loop.create_proxy());
        HeadedEventLoopWaker { proxy }
    }
}
impl EventLoopWaker for HeadedEventLoopWaker {
    fn wake(&self) {
        // kick the OS event loop awake.
        if let Err(err) = self.proxy.wakeup() {
            warn!("Failed to wake up event loop ({}).", err);
        }
    }
    fn clone_box(&self) -> Box<dyn EventLoopWaker> {
        Box::new(HeadedEventLoopWaker {
            proxy: self.proxy.clone(),
        })
    }
}

struct HeadlessEventLoopWaker(Arc<(Mutex<bool>, Condvar)>);
impl EventLoopWaker for HeadlessEventLoopWaker {
    fn wake(&self) {
        // Set the signalling flag and notify the condition variable.
        // This ensures that any sleep operation is interrupted,
        // and any non-sleeping operation will have a change to check
        // the flag before going to sleep.
        let (ref flag, ref condvar) = *self.0;
        let mut flag = flag.lock().unwrap();
        *flag = true;
        condvar.notify_all();
    }
    fn clone_box(&self) -> Box<dyn EventLoopWaker> {
        Box::new(HeadlessEventLoopWaker(self.0.clone()))
    }
}