kvarn/shutdown.rs
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//! Graceful shutdown for Kvarn.
//!
//! This is handled through a [`Manager`] and several helper structs.
//! The `Manager` is returned from [`RunConfig::execute`] and can be awaited
//! to pause execution till the server is shut down.
//! It is also used to trigger a shutdown.
#[cfg_attr(not(feature = "graceful-shutdown"), allow(unused_imports))]
use crate::prelude::{threading::*, *};
#[cfg(feature = "graceful-shutdown")]
use atomic::{AtomicBool, AtomicIsize};
#[cfg(feature = "graceful-shutdown")]
use std::cell::UnsafeCell;
#[cfg(feature = "graceful-shutdown")]
use tokio::sync::watch::{
channel as watch_channel, Receiver as WatchReceiver, Sender as WatchSender,
};
/// Index of [`Waker`] in [`WakerList`].
///
/// Opaque type to safely access the [`UnsafeCell`] of `WakerList`.
#[derive(Debug, Clone, Copy)]
#[cfg(feature = "graceful-shutdown")]
#[repr(transparent)]
pub(crate) struct WakerIndex(usize);
/// Wrapper type for `UnsafeCell<Vec<Option<Waker>>>` to enable sharing across threads.
/// This is safe because of the promises [`WakerIndex`] and the use of this struct below.
#[derive(Debug)]
#[cfg(feature = "graceful-shutdown")]
#[repr(transparent)]
pub(crate) struct WakerList(UnsafeCell<Vec<Option<Waker>>>);
#[cfg(feature = "graceful-shutdown")]
impl WakerList {
pub(crate) fn new(capacity: usize) -> Self {
Self(UnsafeCell::new(Vec::with_capacity(capacity)))
}
pub(crate) fn get_mut(&mut self) -> &mut Vec<Option<Waker>> {
self.0.get_mut()
}
pub(crate) fn get(&self) -> *mut Vec<Option<Waker>> {
self.0.get()
}
/// Notifies all watchers, clearing the list in the process.
/// This is ok since they are called, and register themselves again.
pub(crate) fn notify(&self) {
// See [`Manager::set_waker`] below for safety.
let wakers = unsafe { &mut *self.get() };
for waker in wakers.iter_mut().filter_map(Option::take) {
waker.wake();
}
}
}
#[cfg(feature = "graceful-shutdown")]
unsafe impl Sync for WakerList {}
#[cfg(feature = "graceful-shutdown")]
unsafe impl Send for WakerList {}
/// Shutdown manager.
/// Contains a counter of connections and a shutdown flag
/// to determine when to initiate a shutdown.
///
/// This will wait for all current connections to close, but immediately closes listeners.
///
/// Waiting on shutdown is handled using [`tokio::sync::watch`].
#[derive(Debug)]
#[must_use]
pub struct Manager {
#[cfg(feature = "graceful-shutdown")]
shutdown: AtomicBool,
#[cfg(feature = "graceful-shutdown")]
shutting_down: AtomicBool,
#[cfg(feature = "graceful-shutdown")]
connections: AtomicIsize,
#[cfg(feature = "graceful-shutdown")]
received: AtomicBool,
#[cfg(feature = "graceful-shutdown")]
wakers: std::cell::UnsafeCell<std::sync::Mutex<WakerList>>,
#[cfg(feature = "graceful-shutdown")]
inititate_channel: (WatchSender<()>, WatchReceiver<()>),
#[cfg(feature = "graceful-shutdown")]
finished_channel: (Arc<WatchSender<()>>, WatchReceiver<()>),
#[cfg(feature = "graceful-shutdown")]
pre_shutdown_channel: (
Arc<WatchSender<tokio::sync::mpsc::UnboundedSender<()>>>,
WatchReceiver<tokio::sync::mpsc::UnboundedSender<()>>,
),
#[cfg(feature = "graceful-shutdown")]
pre_shutdown_count: Arc<atomic::AtomicUsize>,
#[cfg(feature = "graceful-shutdown")]
pub(crate) handover_socket_path: Option<PathBuf>,
}
unsafe impl Send for Manager {}
unsafe impl Sync for Manager {}
impl Manager {
/// Creates a new shutdown manager with the capacity of the list of wakers set to `_capacity`.
///
/// # Safety
///
/// `_capacity >= number of add_listener calls`
pub unsafe fn new(_capacity: usize) -> Self {
#[cfg(feature = "graceful-shutdown")]
{
let channel = watch_channel(());
let pre_shutdown_channel = watch_channel(tokio::sync::mpsc::unbounded_channel().0);
Self {
shutdown: AtomicBool::new(false),
shutting_down: AtomicBool::new(false),
connections: AtomicIsize::new(0),
received: AtomicBool::new(false),
wakers: std::cell::UnsafeCell::new(std::sync::Mutex::new(WakerList::new(
_capacity,
))),
inititate_channel: watch_channel(()),
finished_channel: (Arc::new(channel.0), channel.1),
pre_shutdown_channel: (Arc::new(pre_shutdown_channel.0), pre_shutdown_channel.1),
pre_shutdown_count: Arc::new(atomic::AtomicUsize::new(0)),
handover_socket_path: None,
}
}
#[cfg(not(feature = "graceful-shutdown"))]
{
Self {}
}
}
/// Adds a listener to this manager.
///
/// This is used so the `accept` future resolves immediately when the shutdown is triggered.
pub(crate) fn add_listener(&self, listener: Listener) -> AcceptManager {
AcceptManager {
#[cfg(feature = "graceful-shutdown")]
index: {
let mut lock = unsafe { &*self.wakers.get() }.lock().unwrap();
let wakers = lock.get_mut();
let len = wakers.len();
wakers.push(None);
WakerIndex(len)
},
listener,
}
}
/// Gets a watcher for when the shutdown is initiated
#[cfg(feature = "graceful-shutdown")]
pub fn get_initate_shutdown_watcher(&self) -> WatchReceiver<()> {
self.inititate_channel.1.clone()
}
/// Adds to the count of connections.
/// When this connection is closed, you must call [`Manager::remove_connection`]
/// or a logic error will occur and a shutdown will never happen.
pub fn add_connection(&self) {
#[cfg(feature = "graceful-shutdown")]
{
self.connections.fetch_add(1, Ordering::Release);
debug!(
"Current connections: {}",
self.connections.load(Ordering::Acquire)
);
}
}
/// Removes from the count of connections.
/// If the count reaches 0 and the internal shutdown flag is enabled,
/// it will initiate a graceful shutdown.
pub fn remove_connection(&self) {
#[cfg(feature = "graceful-shutdown")]
{
// - 1 at the end because fetch returns the old value.
let connections = self.connections.fetch_sub(1, Ordering::AcqRel) - 1;
if connections < 0 {
warn!(
"Connection count is less than 0. \
This might be an issue if you didn't explicitly \
call `ShutdownManager::remove_connection` in your code."
);
}
if connections <= 0 {
let shutdown = self.shutdown.load(Ordering::Acquire);
if shutdown {
debug!("There are no connections. Shutting down.");
self._shutdown();
}
}
debug!(
"Current connections: {}",
self.connections.load(Ordering::Acquire)
);
}
}
/// Retrieves the number of current connections.
/// Returns `0` if the feature `graceful-shutdown is disabled`.
#[must_use]
pub fn get_connecions(&self) -> isize {
#[cfg(feature = "graceful-shutdown")]
{
self.connections.load(Ordering::Acquire)
}
#[cfg(not(feature = "graceful-shutdown"))]
{
0
}
}
/// Gets the value of the internal shutdown flag. This signals a graceful shutdown is underway.
#[cfg(feature = "graceful-shutdown")]
pub fn get_shutdown(&self, order: Ordering) -> bool {
self.shutdown.load(order)
}
/// # Safety
///
/// We know no other will have mutable access to self by taking `&self`.
/// We only write to a value in memory. If another thread also does so,
/// it does not matter which comes first. Also, only one thread should write to this
/// with the same `index`; this is not a problem since only the Kvarn crate has access to this.
/// This is also upheld by [`WakerIndex`].
///
/// Also, the list never decreases in length, so the index will always be valid.
/// Unless it's extended when this is running. But since we initiate with the necessary
/// capacity (and not less), it **should** never expand.
#[cfg(all(feature = "graceful-shutdown", feature = "async-networking"))]
pub(crate) fn set_waker(&self, index: WakerIndex, waker: Waker) {
let inner = unsafe { &mut *self.wakers.get() };
let inner = inner.get_mut().unwrap();
let wakers = unsafe { &mut *inner.get() };
wakers[index.0] = Some(waker);
}
/// # Safety
///
/// See [`Self::set_waker`].
#[cfg(all(feature = "graceful-shutdown", feature = "async-networking"))]
pub(crate) fn remove_waker(&self, index: WakerIndex) {
let inner = unsafe { &mut *self.wakers.get() };
let inner = inner.get_mut().unwrap();
let wakers = unsafe { &mut *inner.get() };
wakers[index.0] = None;
}
/// Wraps [`Self`] in a [`Arc`] to use across [`tokio::task`]s.
#[must_use]
pub fn build(self) -> Arc<Self> {
Arc::new(self)
}
/// Makes Kvarn perform a graceful shutdown.
///
/// This requires you to be on a thread with a
/// [Tokio runtime](https://docs.rs/tokio/latest/tokio/runtime/struct.Runtime.html).
/// If you create new `std` threads, you can use
/// [`Handle::current()`](https://docs.rs/tokio/latest/tokio/runtime/struct.Handle.html#method.current)
/// to get a movable handle of your runtime. Then call
/// [`Handle::enter`](https://docs.rs/tokio/latest/tokio/runtime/struct.Handle.html#method.enter)
/// at the start of your thread's execution and bind it to a shadow variable
/// (e.g. `let _runtime = runtime_handle.enter()`). That keeps the reference alive during the
/// thread's whole lifespan.
#[cfg(feature = "graceful-shutdown")]
pub fn shutdown(&self) {
info!(
"Initiating shutdown. Handover path: {:?}",
self.handover_socket_path
);
self.shutdown.store(true, Ordering::Release);
self.inititate_channel
.0
.send(())
.expect("we own one receiver");
#[cfg(unix)]
if let Some(path) = &self.handover_socket_path {
std::fs::remove_file(path).ok();
}
if self.connections.load(Ordering::Acquire) <= 0 {
self._shutdown();
}
debug!(
"Current connections: {}",
self.connections.load(Ordering::Acquire)
);
// we stop listening immediately
info!("Notifying wakers.");
unsafe { &*self.wakers.get() }.lock().unwrap().notify();
}
#[cfg(feature = "graceful-shutdown")]
fn _shutdown(&self) {
info!("No connections left. Shutting down.");
if self.shutting_down.swap(true, Ordering::AcqRel) {
return;
}
let channel = self.finished_channel.0.clone();
let pre_channel = self.pre_shutdown_channel.0.clone();
let count = Arc::clone(&self.pre_shutdown_count);
tokio::spawn(async move {
let mut confirmation_channel = tokio::sync::mpsc::unbounded_channel();
// UNWRAP: `self` will always have 1 instance,
// and `self` doesn't get dropped before we tell `channel` to shutdown.
pre_channel.send(confirmation_channel.0).unwrap();
let mut recieved = 0;
let wanted = count.load(Ordering::Acquire);
loop {
if recieved >= wanted {
break;
}
confirmation_channel.1.recv().await;
recieved += 1;
}
info!("Sending shutdown signal");
let _ = channel.send(());
});
}
/// Waits for Kvarn to enter the `shutdown` state.
///
/// This is ran after the [`Self::wait_for_pre_shutdown`] hook, which enables you to do work
/// before this is resolved.
///
/// If the feature `graceful-shutdown` is disabled, this blocks forever.
pub async fn wait(&self) {
#[cfg(feature = "graceful-shutdown")]
{
let mut receiver = WatchReceiver::clone(&self.finished_channel.1);
drop(receiver.changed().await);
// delay shutdown by 0.5s to allow kvarn-signal to send it's messages.
// 500ms is probably way too overkill, maybe 10 would suffice.
// But nothing takes damage from this being larger than it has to.
//
// This is needed because the executable crashes when the uring feature is enabled.
// I think it has something to do with dropping the listeners, which happens after
// this, but before the end of the tokio-uring runtime finishes (adding a sleep to the
// main function doesn't help).
#[cfg(feature = "uring")]
tokio::time::sleep(Duration::from_millis(500)).await;
if !self.received.swap(true, Ordering::SeqCst) {
info!("Received shutdown signal");
}
}
#[cfg(not(feature = "graceful-shutdown"))]
{
std::future::pending::<()>().await;
}
}
/// Hooks into the stage before Kvarn signals it's [shutdown](Self::wait).
/// **Use with care.** See comment below.
///
/// You MUST send `()` to the returned sender ONCE when you are done shutting down.
/// Abuse of this guarantee leads to unwanted timing of shutdown, or none.
///
/// You can call [`Self::shutdown`] before awaiting the returned future.
///
/// If the feature `graceful-shutdown` is disabled, this blocks forever.
#[allow(clippy::manual_async_fn)] // cfg
pub fn wait_for_pre_shutdown(
&self,
) -> impl Future<Output = tokio::sync::mpsc::UnboundedSender<()>> + '_ {
#[cfg(feature = "graceful-shutdown")]
{
let mut receiver = WatchReceiver::clone(&self.pre_shutdown_channel.1);
// we MUST add this before the user can call shutdown, else, it'll load this before the
// future is ran
self.pre_shutdown_count.fetch_add(1, Ordering::SeqCst);
async move {
drop(receiver.changed().await);
info!("Client received pre shutdown signal");
let borrow = receiver.borrow();
(*borrow).clone()
}
}
#[cfg(not(feature = "graceful-shutdown"))]
async {
std::future::pending::<()>().await;
unreachable!()
}
}
}
/// The result of [`AcceptManager::accept`].
/// Can either be a new connection or a shutdown signal.
/// The listener should be dropped right after the shutdown signal is received.
#[must_use]
pub(crate) enum AcceptAction {
/// Shutdown signal; immediately drop this struct.
#[allow(dead_code)]
Shutdown,
/// Accept a new connection or handle a IO error.
AcceptTcp(io::Result<(TcpStream, SocketAddr)>),
/// Accept a new connection or handle a IO error.
#[cfg(feature = "http3")]
AcceptUdp(io::Result<h3_quinn::quinn::Connection>),
}
impl Debug for AcceptAction {
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
match self {
Self::Shutdown => write!(f, "Shutdown"),
Self::AcceptTcp(arg0) => f
.debug_tuple("Accept")
.field(&arg0.as_ref().map(|(_, addr)| addr))
.finish(),
#[cfg(feature = "http3")]
Self::AcceptUdp(arg0) => f
.debug_tuple("Accept")
.field(
&arg0
.as_ref()
.map(h3_quinn::quinn::Connection::remote_address),
)
.finish(),
}
}
}
pub(crate) enum Listener {
Tcp(TcpListener),
#[cfg(feature = "http3")]
Udp(h3_quinn::Endpoint),
}
impl Listener {
pub(crate) fn local_addr(&self) -> SocketAddr {
match self {
Listener::Tcp(tcp) => tcp.local_addr(),
#[cfg(feature = "http3")]
Listener::Udp(udp) => udp.local_addr(),
}
.unwrap_or_else(|_| SocketAddr::V4(net::SocketAddrV4::new(net::Ipv4Addr::LOCALHOST, 0)))
}
}
/// A wrapper around [`TcpListener`] (and `UdpListener` when HTTP/3 comes around)
/// which waits for a new connection **or** a shutdown signal.
#[must_use]
pub(crate) struct AcceptManager {
#[cfg(feature = "graceful-shutdown")]
index: WakerIndex,
listener: Listener,
}
// SAFETY: TcpListener is just an FD, and can be sent across threads.
unsafe impl Send for AcceptManager {}
impl Debug for AcceptManager {
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
let mut s = f.debug_struct(utils::ident_str!(AcceptManager));
utils::fmt_fields!(
s,
#[cfg(feature = "graceful-shutdown")]
(self.index),
(self.listener, &"[TcpListener]".as_clean()),
);
s.finish()
}
}
impl AcceptManager {
/// Waits for a new connection or a shutdown signal.
///
/// Please increase the count of connections on [`Manager`] when this connection is accepted
/// and decrease it when the connection dies.
#[allow(clippy::let_and_return, clippy::no_effect_underscore_binding)] // cfg
pub(crate) async fn accept(&mut self, _manager: &Manager) -> AcceptAction {
#[cfg(feature = "async-networking")]
{
let action = AcceptFuture {
#[cfg(feature = "graceful-shutdown")]
manager: _manager,
#[cfg(feature = "graceful-shutdown")]
index: self.index,
listener: &mut self.listener,
}
.accept()
.await;
#[cfg(feature = "graceful-shutdown")]
_manager.remove_waker(self.index);
action
}
#[cfg(not(feature = "async-networking"))]
{
match &mut self.listener {
Listener::Tcp(tcp) => AcceptAction::AcceptTcp(tcp.accept()),
}
}
}
/// Returns a reference to the inner listener.
#[must_use]
pub(crate) fn inner(&self) -> &Listener {
&self.listener
}
}
#[cfg(feature = "async-networking")]
struct AcceptFuture<'a> {
#[cfg(feature = "graceful-shutdown")]
manager: &'a Manager,
#[cfg(feature = "graceful-shutdown")]
index: WakerIndex,
listener: &'a mut Listener,
}
#[cfg(all(feature = "async-networking", feature = "http3"))]
async fn accept_udp(endpoint: &mut h3_quinn::Endpoint) -> io::Result<h3_quinn::quinn::Connection> {
if let Some(s) = endpoint.accept().await {
s.await.map_err(io::Error::from)
} else {
Err(io::Error::new(
io::ErrorKind::ConnectionReset,
"accept socket finished",
))
}
}
#[cfg(feature = "async-networking")]
impl<'a> AcceptFuture<'a> {
async fn accept(self) -> AcceptAction {
#[cfg(feature = "graceful-shutdown")]
{
trace!(
"Shutting down? {}",
self.manager.shutdown.load(Ordering::Acquire)
);
let shutdown_fut = std::future::poll_fn(|cx| {
if self.manager.shutdown.load(Ordering::Acquire) {
return Poll::Ready(());
}
self.manager.set_waker(self.index, Waker::clone(cx.waker()));
Poll::Pending
});
match self.listener {
Listener::Tcp(tcp) => {
let listener_fut = tcp.accept();
tokio::pin!(shutdown_fut);
#[cfg(feature = "uring")]
tokio::select! {
() = shutdown_fut => AcceptAction::Shutdown,
r = listener_fut => AcceptAction::AcceptTcp(r.map(|(stream, addr)| (TcpStream::new(stream), addr))),
}
#[cfg(not(feature = "uring"))]
tokio::select! {
() = shutdown_fut => AcceptAction::Shutdown,
r = listener_fut => AcceptAction::AcceptTcp(r),
}
}
#[cfg(feature = "http3")]
Listener::Udp(udp) => {
let listener_fut = accept_udp(udp);
tokio::pin!(shutdown_fut);
tokio::select! {
() = shutdown_fut => AcceptAction::Shutdown,
r = listener_fut => AcceptAction::AcceptUdp(r),
}
}
}
}
#[cfg(not(feature = "graceful-shutdown"))]
{
#[cfg(feature = "uring")]
{
match self.listener {
Listener::Tcp(s) => AcceptAction::AcceptTcp(
s.accept()
.await
.map(|(stream, addr)| (TcpStream::new(stream), addr)),
),
#[cfg(feature = "http3")]
Listener::Udp(udp) => AcceptAction::AcceptUdp(accept_udp(udp).await),
}
}
#[cfg(not(feature = "uring"))]
{
match self.listener {
Listener::Tcp(s) => AcceptAction::AcceptTcp(s.accept().await),
#[cfg(feature = "http3")]
Listener::Udp(udp) => AcceptAction::AcceptUdp(accept_udp(udp).await),
}
}
}
}
}