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// Copyright (c) 2018 Nuclear Furnace
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//! `tokio-evacuate` provides a way to safely "evacuate" users of a resource before forcefully
//! removing them.
//!
//! In many networked applications, there comes a time when the server must shutdown or reload, and
//! may still be actively serving traffic. Listeners or publishers can be shut down, and remaining
//! work can be processed while no new work is allowed.. but this may take longer than the operator
//! is comfortable with.
//!
//! `Evacuate` is a middleware future, that works in conjuction with a classic "shutdown signal."
//! By combining a way to track the number of current users, as well as a way to fire a global
//! timeout, we allow applications to provide soft shutdown capabilities, giving work a chance to
//! complete, before forcefully stopping computation.
#[macro_use]
extern crate futures;
extern crate tokio_timer;
#[cfg(test)]
extern crate tokio_executor;
use futures::{
future::Fuse,
prelude::*,
sync::mpsc::{unbounded, UnboundedReceiver, UnboundedSender},
};
use std::time::Duration;
use tokio_timer::{clock::now as clock_now, Delay};
/// Dispatcher for user count updates.
///
/// [`Warden`] is cloneable.
#[derive(Clone)]
pub struct Warden {
pub(crate) notify_tx: UnboundedSender<bool>,
}
/// A future for safely "evacuating" a resource that is used by multiple parties.
///
/// [`Evacuate`] tracks a tripwire, the count of concurrent users, and an evacuation timeout, and
/// functions in a two-step process: we must be tripped, and then we race to the timeout.
///
/// Until the tripwire completes, [`Evacuate`] will always return `Async::NotReady`. Once we detect
/// that the tripwire has completed, however, we immediately spawn a timeout, based on the
/// configured value, and race between the user count dropping to zero and the timeout firing.
///
/// The user count is updated by calls to [`Warden::increment`] and [`Warden::decrement`].
pub struct Evacuate<F: Future> {
count: u64,
notify_rx: UnboundedReceiver<bool>,
tripwire: Fuse<F>,
timeout_ms: u64,
timeout: Delay,
}
impl Warden {
/// Increments the user count.
pub fn increment(&self) { let _ = self.notify_tx.unbounded_send(true); }
/// Decrements the user count.
pub fn decrement(&self) { let _ = self.notify_tx.unbounded_send(false); }
}
impl<F: Future> Evacuate<F> {
/// Creates a new [`Evacuate`].
///
/// The given `tripwire` is used, and the internal timeout is set to the value of `timeout_ms`.
///
/// Returns both a [`Warden`] handle, used for incrementing and decrementing the user count, and
/// [`Evacuate`] itself.
pub fn new(tripwire: F, timeout_ms: u64) -> (Warden, Evacuate<F>) {
let (notify_tx, notify_rx) = unbounded();
let warden = Warden { notify_tx };
let evacuate = Evacuate {
count: 0,
notify_rx,
tripwire: tripwire.fuse(),
timeout_ms,
timeout: Delay::new(clock_now()),
};
(warden, evacuate)
}
}
impl<F: Future> Future for Evacuate<F> {
type Error = ();
type Item = ();
fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
// Drain the notifications queue to make sure we keep getting notified.
while let Ok(Async::Ready(Some(state))) = self.notify_rx.poll() {
if state {
self.count += 1;
} else {
self.count -= 1;
}
}
// We have to wait for our tripwire.
if !self.tripwire.is_done() {
let _ = try_ready!(self.tripwire.poll().map_err(|_| ()));
// If we're here, reset our delay based on the timeout.
self.timeout.reset(clock_now() + Duration::from_millis(self.timeout_ms));
}
// We've tripped, so let's see what we're at for count. If we're at zero, then we're done,
// otherwise, fall through and see if we've hit our delay yet.
if self.count == 0 {
// We've tripped and we're at count 0, so we're done.
return Ok(Async::Ready(()));
}
// Our count isn't at zero, but let's see if we've timed out yet.
self.timeout.poll().map_err(|_| ())
}
}
#[cfg(test)]
mod tests {
extern crate tokio_executor;
#[macro_use]
mod support;
use self::support::*;
use super::Evacuate;
use futures::{
future::{empty, ok},
Future,
};
#[test]
fn test_evacuate_stops_at_tripwire() {
mocked(|_, _| {
let tripwire = empty::<(), ()>();
let (_warden, mut evacuate) = Evacuate::new(tripwire, 10000);
assert_not_ready!(evacuate);
});
}
#[test]
fn test_evacuate_falls_through_on_tripwire() {
mocked(|_, _| {
let tripwire = ok::<(), ()>(());
let (_warden, mut evacuate) = Evacuate::new(tripwire, 10000);
assert_ready!(evacuate);
});
}
#[test]
fn test_evacuate_stops_after_tripping_with_clients() {
mocked(|_, _| {
let tripwire = ok::<(), ()>(());
let (warden, mut evacuate) = Evacuate::new(tripwire, 10000);
warden.increment();
assert_not_ready!(evacuate);
});
}
#[test]
fn test_evacuate_completes_after_client_count_ping_pong() {
mocked(|_, _| {
let tripwire = ok::<(), ()>(());
let (warden, mut evacuate) = Evacuate::new(tripwire, 10000);
warden.increment();
assert_not_ready!(evacuate);
warden.increment();
assert_not_ready!(evacuate);
warden.decrement();
warden.decrement();
assert_ready!(evacuate);
});
}
#[test]
fn test_evacuate_delay_before_clients_hit_zero() {
mocked(|timer, _| {
let tripwire = ok::<(), ()>(());
let (warden, mut evacuate) = Evacuate::new(tripwire, 10000);
warden.increment();
assert_not_ready!(evacuate);
warden.increment();
assert_not_ready!(evacuate);
warden.decrement();
assert_not_ready!(evacuate);
advance(timer, ms(10001));
assert_ready!(evacuate);
});
}
}