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//! Runtime agnostic one-stop solution for graceful shutdown in asynchronous code.
//!
//! This crate addresses two separate but related problems regarding graceful shutdown:
//! * You have to be able to stop running futures when a shutdown signal is given.
//! * You have to be able to wait for futures to finish potential clean-up.
//! * You want to know why the shutdown was triggered (for example to set your process exit code).
//!
//! All of these problems are handled by the [`ShutdownManager`] struct.
//!
//! # Stopping running futures
//! You can get a future to wait for the shutdown signal with [`ShutdownManager::wait_shutdown_triggered()`].
//! In this case you must write your async code to react to the shutdown signal appropriately.
//!
//! Alternatively, you can wrap a future to be cancelled (by being dropped) when the shutdown is triggered with [`ShutdownManager::wrap_cancel()`].
//! This doesn't require the wrapped future to know anything about the shutdown signal,
//! but it also doesn't allow the future to run custom shutdown code.
//!
//! To trigger the shutdown signal, simply call [`ShutdownManager::trigger_shutdown(reason)`][`ShutdownManager::trigger_shutdown()`].
//! The shutdown reason can be any type, as long as it implements [`Clone`].
//! If you want to pass a non-[`Clone`] object or an object that is expensive to clone, you can wrap it in an [`Arc`].
//!
//! # Waiting for futures to complete.
//! You may also want to wait for some futures to complete before actually shutting down instead of just dropping them.
//! This might be important to cleanly shutdown and prevent data loss.
//! You can do that with [`ShutdownManager::wait_shutdown_complete()`].
//! That function returns a future that only completes when the shutdown is "completed".
//!
//! You must also prevent the shutdown from completing too early by calling [`ShutdownManager::delay_shutdown_token()`] or [`ShutdownManager::wrap_delay_shutdown()`].
//! The [`ShutdownManager::delay_shutdown_token()`] function gives you a [`DelayShutdownToken`] which prevents the shutdown from completing.
//! To allow the shutdown to finish, simply drop the token.
//! Alternatively, [`ShutdownManager::wrap_delay_shutdown()`] wraps an existing future,
//! and will prevent the shutdown from completing until the future either completes or is dropped.
//!
//! Note that you can only delay the shutdown completion if it has not completed already.
//! If the shutdown is already complete those functions will return an error.
//!
//! You can also use a token to wrap a future with [`DelayShutdownToken::wrap_future()`].
//! If you already have a token, this allows you to wrap a future without having to worry that the shutdown might already be completed.
//!
//! # Automatically triggering shutdowns
//! You can also trigger a shutdown automatically using a [`TriggerShutdownToken`].
//! Call [`ShutdownManager::trigger_shutdown_token()`] to obtain the token.
//! When the token is dropped, a shutdown is triggered.
//!
//! You can use [`ShutdownManager::wrap_trigger_shutdown()`] or [`TriggerShutdownToken::wrap_future()`] to wrap a future.
//! When the wrapped future completes (or when it is dropped) it will trigger a shutdown.
//! This can be used as a convenient way to trigger a shutdown when a vital task stops.
//!
//! # Futures versus Tasks
//! Be careful when using `JoinHandles` as if they're a regular future.
//! Depending on your async runtime, when you drop a `JoinHandle` this doesn't normally cause the task to stop.
//! It may simply detach the join handle from the task, meaning that your task is still running.
//! If you're not careful, this could still cause data loss on shutdown.
//! As a rule of thumb, you should usually wrap futures *before* you spawn them on a new task.
//!
//! # Example
//!
//! This example is a tokio-based TCP echo server.
//! It simply echos everything it receives from a peer back to that same peer,
//! and it uses this crate for graceful shutdown.
//!
//! This example is also available in the repository as under the name [`tcp-echo-server`] if you want to run it locally.
//!
//! [`tcp-echo-server`]: https://github.com/de-vri-es/async-shutdown-rs/blob/main/examples/tcp-echo-server.rs
//!
//! ```no_run
//! use async_shutdown::ShutdownManager;
//! use std::net::SocketAddr;
//! use tokio::io::{AsyncReadExt, AsyncWriteExt};
//! use tokio::net::{TcpListener, TcpStream};
//!
//! #[tokio::main]
//! async fn main() {
//! // Create a new shutdown object.
//! // We will clone it into all tasks that need it.
//! let shutdown = ShutdownManager::new();
//!
//! // Spawn a task to wait for CTRL+C and trigger a shutdown.
//! tokio::spawn({
//! let shutdown = shutdown.clone();
//! async move {
//! if let Err(e) = tokio::signal::ctrl_c().await {
//! eprintln!("Failed to wait for CTRL+C: {}", e);
//! std::process::exit(1);
//! } else {
//! eprintln!("\nReceived interrupt signal. Shutting down server...");
//! shutdown.trigger_shutdown(0).ok();
//! }
//! }
//! });
//!
//! // Run the server and set a non-zero exit code if we had an error.
//! let exit_code = match run_server(shutdown.clone(), "[::]:9372").await {
//! Ok(()) => {
//! shutdown.trigger_shutdown(0).ok();
//! },
//! Err(e) => {
//! eprintln!("Server task finished with an error: {}", e);
//! shutdown.trigger_shutdown(1).ok();
//! },
//! };
//!
//! // Wait for clients to run their cleanup code, then exit.
//! // Without this, background tasks could be killed before they can run their cleanup code.
//! let exit_code = shutdown.wait_shutdown_complete().await;
//!
//! std::process::exit(exit_code);
//! }
//!
//! async fn run_server(shutdown: ShutdownManager<i32>, bind_address: &str) -> std::io::Result<()> {
//! let server = TcpListener::bind(&bind_address).await?;
//! eprintln!("Server listening on {}", bind_address);
//!
//! // Simply use `wrap_cancel` for everything, since we do not need clean-up for the listening socket.
//! // See `handle_client` for a case where a future is given the time to perform logging after the shutdown was triggered.
//! while let Ok(connection) = shutdown.wrap_cancel(server.accept()).await {
//! let (stream, address) = connection?;
//! tokio::spawn(handle_client(shutdown.clone(), stream, address));
//! }
//!
//! Ok(())
//! }
//!
//! async fn handle_client(shutdown: ShutdownManager<i32>, mut stream: TcpStream, address: SocketAddr) {
//! eprintln!("Accepted new connection from {}", address);
//!
//! // Make sure the shutdown doesn't complete until the delay token is dropped.
//! //
//! // Getting the token will fail if the shutdown has already started,
//! // in which case we just log a message and return.
//! //
//! // If you already have a future that should be allowed to complete,
//! // you can also use `shutdown.wrap_delay_shutdown(...)`.
//! // Here it is easier to use a token though.
//! let _delay_token = match shutdown.delay_shutdown_token() {
//! Ok(token) => token,
//! Err(_) => {
//! eprintln!("Shutdown already started, closing connection with {}", address);
//! return;
//! }
//! };
//!
//! // Now run the echo loop, but cancel it when the shutdown is triggered.
//! match shutdown.wrap_cancel(echo_loop(&mut stream)).await {
//! Ok(Err(e)) => eprintln!("Error in connection {}: {}", address, e),
//! Ok(Ok(())) => eprintln!("Connection closed by {}", address),
//! Err(_exit_code) => eprintln!("Shutdown triggered, closing connection with {}", address),
//! }
//!
//! // The delay token will be dropped here, allowing the shutdown to complete.
//! }
//!
//! async fn echo_loop(stream: &mut TcpStream) -> std::io::Result<()> {
//! // Echo everything we receive back to the peer in a loop.
//! let mut buffer = vec![0; 512];
//! loop {
//! let read = stream.read(&mut buffer).await?;
//! if read == 0 {
//! break;
//! }
//! stream.write(&buffer[..read]).await?;
//! }
//!
//! Ok(())
//! }
//! ```
#![warn(missing_docs)]
use std::future::Future;
use std::sync::{Arc, Mutex};
mod shutdown_complete;
pub use shutdown_complete::ShutdownComplete;
mod shutdown_signal;
pub use shutdown_signal::ShutdownSignal;
mod wrap_cancel;
use waker_list::WakerList;
pub use wrap_cancel::WrapCancel;
mod wrap_trigger_shutdown;
pub use wrap_trigger_shutdown::WrapTriggerShutdown;
mod wrap_delay_shutdown;
pub use wrap_delay_shutdown::WrapDelayShutdown;
mod waker_list;
/// Shutdown manager for asynchronous tasks and futures.
///
/// The shutdown manager allows you to:
/// * Signal futures to shutdown or forcibly cancel them (by dropping them).
/// * Wait for futures to perform their clean-up after a shutdown was triggered.
/// * Retrieve the shutdown reason after the shutdown was triggered.
///
/// The shutdown manager can be cloned and shared with multiple tasks.
/// Each clone uses the same internal state.
#[derive(Clone)]
pub struct ShutdownManager<T: Clone> {
inner: Arc<Mutex<ShutdownManagerInner<T>>>,
}
impl<T: Clone> ShutdownManager<T> {
/// Create a new shutdown manager.
#[inline]
pub fn new() -> Self {
Self {
inner: Arc::new(Mutex::new(ShutdownManagerInner::new())),
}
}
/// Check if the shutdown has been triggered.
#[inline]
pub fn is_shutdown_triggered(&self) -> bool {
self.inner.lock().unwrap().shutdown_reason.is_some()
}
/// Check if the shutdown has completed.
#[inline]
pub fn is_shutdown_completed(&self) -> bool {
let inner = self.inner.lock().unwrap();
inner.shutdown_reason.is_some() && inner.delay_tokens == 0
}
/// Get the shutdown reason, if the shutdown has been triggered.
///
/// Returns [`None`] if the shutdown has not been triggered yet.
#[inline]
pub fn shutdown_reason(&self) -> Option<T> {
self.inner.lock().unwrap().shutdown_reason.clone()
}
/// Asynchronously wait for the shutdown to be triggered.
///
/// This returns a future that completes when the shutdown is triggered.
/// The future can be cloned and sent to other threads or tasks freely.
///
/// If the shutdown is already triggered, the returned future immediately resolves.
///
/// You can also use `ShutdownSignal::wrap_cancel()` of the returned object
/// to automatically cancel a future when the shutdown signal is received.
/// This is identical to `Self::wrap_cancel()`.
#[inline]
pub fn wait_shutdown_triggered(&self) -> ShutdownSignal<T> {
ShutdownSignal {
inner: self.inner.clone(),
waker_token: None,
}
}
/// Asynchronously wait for the shutdown to complete.
///
/// This returns a future that completes when the shutdown is complete.
/// The future can be cloned and sent to other threads or tasks freely.
///
/// The shutdown is complete when all [`DelayShutdownToken`] are dropped
/// and all [`WrapDelayShutdown`] futures have completed or are dropped.
#[inline]
pub fn wait_shutdown_complete(&self) -> ShutdownComplete<T> {
ShutdownComplete {
inner: self.inner.clone(),
waker_token: None,
}
}
/// Trigger the shutdown.
///
/// This will cause all [`ShutdownSignal`] and [`WrapCancel`] futures associated with this shutdown manager to be resolved.
///
/// The shutdown will not be considered complete until all [`DelayShutdownTokens`][DelayShutdownToken] are dropped.
///
/// If the shutdown was already started, this function returns an error.
#[inline]
pub fn trigger_shutdown(&self, reason: T) -> Result<(), ShutdownAlreadyStarted<T>> {
self.inner.lock().unwrap().shutdown(reason)
}
/// Wrap a future so that it is cancelled (dropped) when the shutdown is triggered.
///
/// The returned future completes with `Err(shutdown_reason)` if the shutdown is triggered,
/// and with `Ok(x)` if the wrapped future completes first.
#[inline]
pub fn wrap_cancel<F: Future>(&self, future: F) -> WrapCancel<T, F> {
self.wait_shutdown_triggered().wrap_cancel(future)
}
/// Wrap a future to cause a shutdown when the future completes or when it is dropped.
#[inline]
pub fn wrap_trigger_shutdown<F: Future>(&self, shutdown_reason: T, future: F) -> WrapTriggerShutdown<T, F> {
self.trigger_shutdown_token(shutdown_reason).wrap_future(future)
}
/// Wrap a future to delay shutdown completion until the wrapped future completes or until it is dropped.
///
/// The returned future transparently completes with the value of the wrapped future.
/// However, the shutdown will not be considered complete until the wrapped future completes or is dropped.
///
/// If the shutdown has already completed, this function returns an error.
#[inline]
pub fn wrap_delay_shutdown<F: Future>(&self, future: F) -> Result<WrapDelayShutdown<T, F>, ShutdownAlreadyCompleted<T>> {
Ok(self.delay_shutdown_token()?.wrap_future(future))
}
/// Get a token that delays shutdown completion as long as it exists.
///
/// The manager keeps track of all the tokens it hands out.
/// The tokens can be cloned and sent to different threads and tasks.
/// All tokens (including the clones) must be dropped before the shutdown is considered to be complete.
///
/// If the shutdown has already completed, this function returns an error.
///
/// If you want to delay the shutdown until a future completes,
/// consider using [`Self::wrap_delay_shutdown()`] instead.
#[inline]
pub fn delay_shutdown_token(&self) -> Result<DelayShutdownToken<T>, ShutdownAlreadyCompleted<T>> {
let mut inner = self.inner.lock().unwrap();
// Shutdown already completed, can't delay completion anymore.
if inner.delay_tokens == 0 {
if let Some(reason) = &inner.shutdown_reason {
return Err(ShutdownAlreadyCompleted::new(reason.clone()));
}
}
inner.increase_delay_count();
Ok(DelayShutdownToken {
inner: self.inner.clone(),
})
}
/// Get a token that triggers a shutdown when dropped.
///
/// When a [`TriggerShutdownToken`] is dropped, the shutdown is triggered automatically.
/// This applies to *any* token.
/// If you clone a token five times and drop one of them, it will trigger a shutdown/
///
/// You can also use [`Self::wrap_trigger_shutdown()`] to wrap a future so that a shutdown is triggered
/// when the future completes or if it is dropped.
#[inline]
pub fn trigger_shutdown_token(&self, shutdown_reason: T) -> TriggerShutdownToken<T> {
TriggerShutdownToken {
shutdown_reason: Arc::new(Mutex::new(Some(shutdown_reason))),
inner: self.inner.clone(),
}
}
}
impl<T: Clone> Default for ShutdownManager<T> {
#[inline]
fn default() -> Self {
Self::new()
}
}
/// Token that delays shutdown completion as long as it exists.
///
/// The token can be cloned and sent to different threads and tasks freely.
///
/// All clones must be dropped before the shutdown can complete.
pub struct DelayShutdownToken<T: Clone> {
inner: Arc<Mutex<ShutdownManagerInner<T>>>,
}
impl<T: Clone> DelayShutdownToken<T> {
/// Wrap a future to delay shutdown completion until the wrapped future completes or until it is dropped.
///
/// This consumes the token to avoid keeping an unused token around by accident, which would delay shutdown indefinitely.
/// If you wish to use the token multiple times, you can clone it first:
/// ```
/// # let shutdown = async_shutdown::ShutdownManager::<()>::new();
/// # let delay_shutdown_token = shutdown.delay_shutdown_token().unwrap();
/// # let future = async { () };
/// let future = delay_shutdown_token.clone().wrap_future(future);
/// ```
///
/// The returned future transparently completes with the value of the wrapped future.
/// However, the shutdown will not be considered complete until the future completes or is dropped.
#[inline]
pub fn wrap_future<F: Future>(self, future: F) -> WrapDelayShutdown<T, F> {
WrapDelayShutdown {
delay_token: Some(self),
future,
}
}
}
impl<T: Clone> Clone for DelayShutdownToken<T> {
#[inline]
fn clone(&self) -> Self {
self.inner.lock().unwrap().increase_delay_count();
DelayShutdownToken {
inner: self.inner.clone(),
}
}
}
impl<T: Clone> Drop for DelayShutdownToken<T> {
#[inline]
fn drop(&mut self) {
self.inner.lock().unwrap().decrease_delay_count();
}
}
/// Token that triggers a shutdown when it is dropped.
///
/// The token can be cloned and sent to different threads and tasks freely.
/// If *one* of the cloned tokens is dropped, a shutdown is triggered.
/// Even if the rest of the clones still exist.
#[derive(Clone)]
pub struct TriggerShutdownToken<T: Clone> {
shutdown_reason: Arc<Mutex<Option<T>>>,
inner: Arc<Mutex<ShutdownManagerInner<T>>>,
}
impl<T: Clone> TriggerShutdownToken<T> {
/// Wrap a future to trigger a shutdown when it completes or is dropped.
///
/// This consumes the token to avoid accidentally dropping the token
/// after wrapping a future and instantly causing a shutdown.
///
/// If you need to keep the token around, you can clone it first:
/// ```
/// # let trigger_shutdown_token = async_shutdown::ShutdownManager::new().trigger_shutdown_token(());
/// # let future = async { () };
/// let future = trigger_shutdown_token.clone().wrap_future(future);
/// ```
#[inline]
pub fn wrap_future<F: Future>(self, future: F) -> WrapTriggerShutdown<T, F> {
WrapTriggerShutdown {
trigger_shutdown_token: Some(self),
future,
}
}
/// Drop the token without causing a shutdown.
///
/// This is equivalent to calling [`std::mem::forget()`] on the token.
#[inline]
pub fn forget(self) {
std::mem::forget(self)
}
}
impl<T: Clone> Drop for TriggerShutdownToken<T> {
#[inline]
fn drop(&mut self) {
let mut inner = self.inner.lock().unwrap();
let reason = self.shutdown_reason.lock().unwrap().take();
if let Some(reason) = reason {
inner.shutdown(reason).ok();
}
}
}
struct ShutdownManagerInner<T> {
/// The shutdown reason.
shutdown_reason: Option<T>,
/// Number of delay tokens in existence.
///
/// Must reach 0 before shutdown can complete.
delay_tokens: usize,
/// Tasks to wake when a shutdown is triggered.
on_shutdown: WakerList,
/// Tasks to wake when the shutdown is complete.
on_shutdown_complete: WakerList,
}
impl<T: Clone> ShutdownManagerInner<T> {
fn new() -> Self {
Self {
shutdown_reason: None,
delay_tokens: 0,
on_shutdown_complete: WakerList::new(),
on_shutdown: WakerList::new(),
}
}
fn increase_delay_count(&mut self) {
self.delay_tokens += 1;
}
fn decrease_delay_count(&mut self) {
self.delay_tokens -= 1;
if self.delay_tokens == 0 {
self.notify_shutdown_complete();
}
}
fn shutdown(&mut self, reason: T) -> Result<(), ShutdownAlreadyStarted<T>> {
match &self.shutdown_reason {
Some(original_reason) => {
Err(ShutdownAlreadyStarted::new(original_reason.clone(), reason))
},
None => {
self.shutdown_reason = Some(reason);
self.on_shutdown.wake_all();
if self.delay_tokens == 0 {
self.notify_shutdown_complete()
}
Ok(())
},
}
}
fn notify_shutdown_complete(&mut self) {
self.on_shutdown_complete.wake_all();
}
}
/// Error returned when you try to trigger the shutdown multiple times on the same [`ShutdownManager`].
#[derive(Debug, Clone)]
#[non_exhaustive]
pub struct ShutdownAlreadyStarted<T> {
/// The shutdown reason of the already started shutdown.
pub shutdown_reason: T,
/// The provided reason that was ignored because the shutdown was already started.
pub ignored_reason: T,
}
impl<T> ShutdownAlreadyStarted<T> {
pub(crate) const fn new(shutdown_reason: T, ignored_reason:T ) -> Self {
Self { shutdown_reason, ignored_reason }
}
}
impl<T: std::fmt::Debug> std::error::Error for ShutdownAlreadyStarted<T> {}
impl<T> std::fmt::Display for ShutdownAlreadyStarted<T> {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
write!(f, "shutdown has already started, can not delay shutdown completion")
}
}
/// Error returned when trying to delay a shutdown that has already completed.
#[derive(Debug)]
#[non_exhaustive]
pub struct ShutdownAlreadyCompleted<T> {
/// The shutdown reason of the already completed shutdown.
pub shutdown_reason: T,
}
impl<T> ShutdownAlreadyCompleted<T> {
pub(crate) const fn new(shutdown_reason: T) -> Self {
Self { shutdown_reason }
}
}
impl<T: std::fmt::Debug> std::error::Error for ShutdownAlreadyCompleted<T> {}
impl<T> std::fmt::Display for ShutdownAlreadyCompleted<T> {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
write!(f, "shutdown has already completed, can not delay shutdown completion")
}
}