Implement native timers

Native timers are a much hairier thing to deal with than green timers due to the
interface that we would like to expose (both a blocking sleep() and a
channel-based interface). I ended up implementing timers in three different ways
for the various platforms that we supports.

In all three of the implementations, there is a worker thread which does send()s
on channels for timers. This worker thread is initialized once and then
communicated to in a platform-specific manner, but there's always a shared
channel available for sending messages to the worker thread.

* Windows - I decided to use windows kernel timer objects via
  CreateWaitableTimer and SetWaitableTimer in order to provide sleeping
  capabilities. The worker thread blocks via WaitForMultipleObjects where one of
  the objects is an event that is used to wake up the helper thread (which then
  drains the incoming message channel for requests).

* Linux/(Android?) - These have the ideal interface for implementing timers,
  timerfd_create. Each timer corresponds to a timerfd, and the helper thread
  uses epoll to wait for all active timers and then send() for the next one that
  wakes up. The tricky part in this implementation is updating a timerfd, but
  see the implementation for the fun details

* OSX/FreeBSD - These obviously don't have the windows APIs, and sadly don't
  have the timerfd api available to them, so I have thrown together a solution
  which uses select() plus a timeout in order to ad-hoc-ly implement a timer
  solution for threads. The implementation is backed by a sorted array of timers
  which need to fire. As I said, this is an ad-hoc solution which is certainly
  not accurate timing-wise. I have done this implementation due to the lack of
  other primitives to provide an implementation, and I've done it the best that
  I could, but I'm sure that there's room for improvement.

I'm pretty happy with how these implementations turned out. In theory we could
drop the timerfd implementation and have linux use the select() + timeout
implementation, but it's so inaccurate that I would much rather continue to use
timerfd rather than my ad-hoc select() implementation.

The only change that I would make to the API in general is to have a generic
sleep() method on an IoFactory which doesn't require allocating a Timer object.
For everything but windows it's super-cheap to request a blocking sleep for a
set amount of time, and it's probably worth it to provide a sleep() which
doesn't do something like allocate a file descriptor on linux.

1 files changed, 303 insertions, 0 deletions

diff --git a/src/libnative/io/timer_timerfd.rs b/src/libnative/io/timer_timerfd.rs
new file mode 100644
index 00000000000..4912f4f431f
--- /dev/null
+++ b/src/libnative/io/timer_timerfd.rs
@@ -0,0 +1,303 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Timers based on timerfd_create(2)
+//!
+//! On OSes which support timerfd_create, we can use these much more accurate
+//! timers over select() + a timeout (see timer_other.rs). This strategy still
+//! employs a worker thread which does the waiting on the timer fds (to send
+//! messages away).
+//!
+//! The worker thread in this implementation uses epoll(7) to block. It
+//! maintains a working set of *all* native timers in the process, along with a
+//! pipe file descriptor used to communicate that there is data available on the
+//! incoming channel to the worker thread. Timers send requests to update their
+//! timerfd settings to the worker thread (see the comment above 'oneshot' for
+//! why).
+//!
+//! As with timer_other, timers just using sleep() do not use the timerfd at
+//! all. They remove the timerfd from the worker thread and then invoke usleep()
+//! to block the calling thread.
+//!
+//! As with timer_other, all units in this file are in units of millseconds.
+
+use std::comm::Data;
+use std::libc;
+use std::ptr;
+use std::os;
+use std::rt::rtio;
+use std::hashmap::HashMap;
+use std::unstable::intrinsics;
+
+use io::file::FileDesc;
+use io::IoResult;
+use io::timer_helper;
+
+pub struct Timer {
+    priv fd: FileDesc,
+    priv on_worker: bool,
+}
+
+pub enum Req {
+    NewTimer(libc::c_int, Chan<()>, bool, imp::itimerspec),
+    RemoveTimer(libc::c_int, Chan<()>),
+    Shutdown,
+}
+
+fn helper(input: libc::c_int, messages: Port<Req>) {
+    let efd = unsafe { imp::epoll_create(10) };
+    let _fd1 = FileDesc::new(input, true);
+    let _fd2 = FileDesc::new(efd, true);
+
+    fn add(efd: libc::c_int, fd: libc::c_int) {
+        let event = imp::epoll_event {
+            events: imp::EPOLLIN as u32,
+            data: imp::epoll_data_t { fd: fd, pad: 0, }
+        };
+        let ret = unsafe {
+            imp::epoll_ctl(efd, imp::EPOLL_CTL_ADD, fd, &event)
+        };
+        assert_eq!(ret, 0);
+    }
+    fn del(efd: libc::c_int, fd: libc::c_int) {
+        let event = imp::epoll_event {
+            events: 0, data: imp::epoll_data_t { fd: 0, pad: 0, }
+        };
+        let ret = unsafe {
+            imp::epoll_ctl(efd, imp::EPOLL_CTL_DEL, fd, &event)
+        };
+        assert_eq!(ret, 0);
+    }
+
+    add(efd, input);
+    let events: [imp::epoll_event, ..16] = unsafe { intrinsics::init() };
+    let mut map: HashMap<libc::c_int, (Chan<()>, bool)> = HashMap::new();
+    'outer: loop {
+        let n = match unsafe {
+            imp::epoll_wait(efd, events.as_ptr(),
+                            events.len() as libc::c_int, -1)
+        } {
+            0 => fail!("epoll_wait returned immediately!"),
+            -1 => fail!("epoll wait failed: {}", os::last_os_error()),
+            n => n
+        };
+
+        let mut incoming = false;
+        debug!("{} events to process", n);
+        for event in events.slice_to(n as uint).iter() {
+            let fd = event.data.fd;
+            debug!("data on fd {} (input = {})", fd, input);
+            if fd == input {
+                let mut buf = [0, ..1];
+                // drain the input file descriptor of its input
+                FileDesc::new(fd, false).inner_read(buf);
+                incoming = true;
+            } else {
+                let mut bits = [0, ..8];
+                // drain the timerfd of how many times its fired
+                //
+                // XXX: should this perform a send() this number of
+                //      times?
+                FileDesc::new(fd, false).inner_read(bits);
+                let remove = {
+                    match map.find(&fd).expect("fd unregistered") {
+                        &(ref c, oneshot) => !c.try_send(()) || oneshot
+                    }
+                };
+                if remove {
+                    map.remove(&fd);
+                    del(efd, fd);
+                }
+            }
+        }
+
+        while incoming {
+            match messages.try_recv() {
+                Data(NewTimer(fd, chan, one, timeval)) => {
+                    // acknowledge we have the new channel, we will never send
+                    // another message to the old channel
+                    chan.send(());
+
+                    // If we haven't previously seen the file descriptor, then
+                    // we need to add it to the epoll set.
+                    if map.insert(fd, (chan, one)) {
+                        add(efd, fd);
+                    }
+
+                    // Update the timerfd's time value now that we have control
+                    // of the timerfd
+                    let ret = unsafe {
+                        imp::timerfd_settime(fd, 0, &timeval, ptr::null())
+                    };
+                    assert_eq!(ret, 0);
+                }
+
+                Data(RemoveTimer(fd, chan)) => {
+                    if map.remove(&fd) {
+                        del(efd, fd);
+                    }
+                    chan.send(());
+                }
+
+                Data(Shutdown) => {
+                    assert!(map.len() == 0);
+                    break 'outer;
+                }
+
+                _ => break,
+            }
+        }
+    }
+}
+
+impl Timer {
+    pub fn new() -> IoResult<Timer> {
+        timer_helper::boot(helper);
+        match unsafe { imp::timerfd_create(imp::CLOCK_MONOTONIC, 0) } {
+            -1 => Err(super::last_error()),
+            n => Ok(Timer { fd: FileDesc::new(n, true), on_worker: false, }),
+        }
+    }
+
+    pub fn sleep(ms: u64) {
+        unsafe { libc::usleep((ms * 1000) as libc::c_uint); }
+    }
+
+    fn remove(&mut self) {
+        if !self.on_worker { return }
+
+        let (p, c) = Chan::new();
+        timer_helper::send(RemoveTimer(self.fd.fd(), c));
+        p.recv();
+        self.on_worker = false;
+    }
+}
+
+impl rtio::RtioTimer for Timer {
+    fn sleep(&mut self, msecs: u64) {
+        self.remove();
+        Timer::sleep(msecs);
+    }
+
+    // Periodic and oneshot channels are updated by updating the settings on the
+    // corresopnding timerfd. The update is not performed on the thread calling
+    // oneshot or period, but rather the helper epoll thread. The reason for
+    // this is to avoid losing messages and avoid leaking messages across ports.
+    //
+    // By updating the timerfd on the helper thread, we're guaranteed that all
+    // messages for a particular setting of the timer will be received by the
+    // new channel/port pair rather than leaking old messages onto the new port
+    // or leaking new messages onto the old port.
+    //
+    // We also wait for the remote thread to actually receive the new settings
+    // before returning to guarantee the invariant that when oneshot() and
+    // period() return that the old port will never receive any more messages.
+
+    fn oneshot(&mut self, msecs: u64) -> Port<()> {
+        let (p, c) = Chan::new();
+
+        let new_value = imp::itimerspec {
+            it_interval: imp::timespec { tv_sec: 0, tv_nsec: 0 },
+            it_value: imp::timespec {
+                tv_sec: (msecs / 1000) as libc::time_t,
+                tv_nsec: ((msecs % 1000) * 1000000) as libc::c_long,
+            }
+        };
+        timer_helper::send(NewTimer(self.fd.fd(), c, true, new_value));
+        p.recv();
+        self.on_worker = true;
+
+        return p;
+    }
+
+    fn period(&mut self, msecs: u64) -> Port<()> {
+        let (p, c) = Chan::new();
+
+        let spec = imp::timespec {
+            tv_sec: (msecs / 1000) as libc::time_t,
+            tv_nsec: ((msecs % 1000) * 1000000) as libc::c_long,
+        };
+        let new_value = imp::itimerspec { it_interval: spec, it_value: spec, };
+        timer_helper::send(NewTimer(self.fd.fd(), c, false, new_value));
+        p.recv();
+        self.on_worker = true;
+
+        return p;
+    }
+}
+
+impl Drop for Timer {
+    fn drop(&mut self) {
+        // When the timerfd file descriptor is closed, it will be automatically
+        // removed from the epoll set of the worker thread, but we want to make
+        // sure that the associated channel is also removed from the worker's
+        // hash map.
+        self.remove();
+    }
+}
+
+#[allow(dead_code)]
+mod imp {
+    use std::libc;
+
+    pub static CLOCK_MONOTONIC: libc::c_int = 1;
+    pub static EPOLL_CTL_ADD: libc::c_int = 1;
+    pub static EPOLL_CTL_DEL: libc::c_int = 2;
+    pub static EPOLL_CTL_MOD: libc::c_int = 3;
+    pub static EPOLLIN: libc::c_int = 0x001;
+    pub static EPOLLOUT: libc::c_int = 0x004;
+    pub static EPOLLPRI: libc::c_int = 0x002;
+    pub static EPOLLERR: libc::c_int = 0x008;
+    pub static EPOLLRDHUP: libc::c_int = 0x2000;
+    pub static EPOLLET: libc::c_int = 1 << 31;
+    pub static EPOLLHUP: libc::c_int = 0x010;
+    pub static EPOLLONESHOT: libc::c_int = 1 << 30;
+
+    pub struct epoll_event {
+        events: u32,
+        data: epoll_data_t,
+    }
+
+    pub struct epoll_data_t {
+        fd: i32,
+        pad: u32,
+    }
+
+    pub struct timespec {
+        tv_sec: libc::time_t,
+        tv_nsec: libc::c_long,
+    }
+
+    pub struct itimerspec {
+        it_interval: timespec,
+        it_value: timespec,
+    }
+
+    extern {
+        pub fn timerfd_create(clockid: libc::c_int,
+                              flags: libc::c_int) -> libc::c_int;
+        pub fn timerfd_settime(fd: libc::c_int,
+                               flags: libc::c_int,
+                               new_value: *itimerspec,
+                               old_value: *itimerspec) -> libc::c_int;
+        pub fn timerfd_gettime(fd: libc::c_int,
+                               curr_value: *itimerspec) -> libc::c_int;
+
+        pub fn epoll_create(size: libc::c_int) -> libc::c_int;
+        pub fn epoll_ctl(epfd: libc::c_int,
+                         op: libc::c_int,
+                         fd: libc::c_int,
+                         event: *epoll_event) -> libc::c_int;
+        pub fn epoll_wait(epfd: libc::c_int,
+                          events: *epoll_event,
+                          maxevents: libc::c_int,
+                          timeout: libc::c_int) -> libc::c_int;
+    }
+}