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//! tokio-task-tracker is a simple graceful shutdown solution for tokio.
//!
//! The basic idea is to use a `TaskSpawner` to create `TaskTracker` object, and hold
//! on to them in spawned tasks. Inside the task, you can check `tracker.cancelled().await`
//! to wait for the task to be cancelled.
//!
//! The `TaskWaiter` can be used to wait for an interrupt and then wait for all
//! `TaskTracker`s to be dropped.
//!
//! # Examples
//!
//! ```no_run
//! # use std::time::Duration;
//! #
//! #[tokio::main(flavor = "current_thread")]
//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
//! let (spawner, waiter) = tokio_task_tracker::new();
//!
//! // Start a task
//! spawner.spawn(|tracker| async move {
//! tokio::select! {
//! _ = tracker.cancelled() => {
//! // The token was cancelled, task should shut down.
//! }
//! _ = tokio::time::sleep(Duration::from_secs(9999)) => {
//! // Long work has completed
//! }
//! }
//! });
//!
//! // Wait for all tasks to complete, or for someone to hit ctrl-c.
//! // If tasks down't complete within 5 seconds, we'll quit anyways.
//! waiter.wait_for_shutdown(Duration::from_secs(5)).await?;
//!
//! Ok(())
//! }
//! ```
//!
//! If you do not wish to allow a task to be aborted, you still need to make sure
//! the task captures the tracker, because TaskWaiter will wait for all trackers to be dropped:
//!
//! ```no_run
//! # use std::time::Duration;
//! #
//! # #[tokio::main(flavor = "current_thread")]
//! # async fn main() {
//! # let (spawner, waiter) = tokio_task_tracker::new();
//! #
//! // Start a task
//! spawner.spawn(|tracker| async move {
//! // Move the tracker into the task.
//! let _tracker = tracker;
//!
//! // Do some work that we don't want to abort.
//! tokio::time::sleep(Duration::from_secs(9999)).await;
//! });
//!
//! # }
//! ```
//!
//! You can also create a tracker via the `task` method:
//!
//! ```no_run
//! # use std::time::Duration;
//! #
//! # #[tokio::main(flavor = "current_thread")]
//! # async fn main() {
//! # let (spawner, waiter) = tokio_task_tracker::new();
//! #
//! // Start a task
//! let tracker = spawner.task();
//! tokio::task::spawn(async move {
//! // Move the tracker into the task.
//! let _tracker = tracker;
//!
//! // ...
//! });
//!
//! # }
//! ```
//!
//! Trackers can be used to spawn subtasks via `tracker.subtask()` or
//! `tracker.spawn()`.
use std::{
future::Future,
sync::{Arc, Mutex},
time::Duration,
};
use shutdown::wait_for_shutdown_signal;
use tokio::{select, sync::mpsc, task::JoinHandle};
use tokio_util::sync::CancellationToken;
mod shutdown;
/// Builder is used to create a TaskSpawner and TaskWaiter.
pub struct Builder {
token: Option<CancellationToken>,
}
/// TaskSpawner is used to spawn new task trackers.
#[derive(Clone)]
pub struct TaskSpawner {
token: CancellationToken,
stop_tx: Arc<Mutex<Option<mpsc::Sender<()>>>>,
}
/// TaskWaiter is used to wait until all task trackers have been dropped.
pub struct TaskWaiter {
token: CancellationToken,
/// Shared stop_tx is shared between all TaskSpawners and the TaskWaiter, so that
/// when we call TaskWaiter::wait() we can drop the tx from all spawners.
stop_tx: Arc<Mutex<Option<mpsc::Sender<()>>>>,
stop_rx: mpsc::Receiver<()>,
}
/// A TaskTracker is used both as a token to keep track of active tasks, and
/// as a cancellation token to check to see if the current task should quit.
#[derive(Clone)]
pub struct TaskTracker {
token: CancellationToken,
// Hang on to an instance of tx. We do this so we can know when all tasks
// have been completed.
_stop_tx: Option<mpsc::Sender<()>>,
}
#[derive(Debug, PartialEq)]
pub enum Error {
/// Returned when we timeout waiting for all tasks to shut down.
Timeout,
/// Returned when we cannot bind to the interrupt/terminate signals.
CouldNotBindInterrupt,
/// Returned when we were waiting for graceful shutdown, but received a
/// second interrupt signal.
ShutdownEarly,
}
impl std::error::Error for Error {}
impl std::fmt::Display for Error {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Error::Timeout => write!(f, "Not all tasks finished before timeout"),
Error::CouldNotBindInterrupt => write!(f, "Could not bind interrupt handler"),
Error::ShutdownEarly => write!(f, "Skipping graceful shutdown due to second interrupt"),
}
}
}
/// Create a new TaskSpawner and TaskWaiter.
pub fn new() -> (TaskSpawner, TaskWaiter) {
Builder::default().build()
}
impl Builder {
/// Create a new Builder.
pub fn new() -> Self {
Builder { token: None }
}
/// Use an existing CancellationToken for the returned TaskWaiter and TaskSpawner.
/// If the given token is cancelled, all associated TaskTrackers will be cancelled
/// as well.
pub fn set_cancellation_token(mut self, token: CancellationToken) -> Self {
self.token = Some(token);
self
}
/// Create a new TaskSpawner and TaskWaiter.
pub fn build(self) -> (TaskSpawner, TaskWaiter) {
let (stop_tx, stop_rx) = mpsc::channel(1);
let stop_tx = Arc::new(Mutex::new(Some(stop_tx)));
let token = self.token.unwrap_or(CancellationToken::new());
(
TaskSpawner {
token: token.clone(),
stop_tx: stop_tx.clone(),
},
TaskWaiter {
token,
stop_tx,
stop_rx,
},
)
}
}
impl Default for Builder {
fn default() -> Self {
Self::new()
}
}
impl TaskSpawner {
/// Create a new TaskTracker.
pub fn task(&self) -> TaskTracker {
TaskTracker {
token: self.token.clone(),
_stop_tx: self.stop_tx.lock().unwrap().as_ref().cloned(),
}
}
/// Spawn a task.
///
/// The given closure will be called, passing in a task tracker.
pub fn spawn<T, F: FnOnce(TaskTracker) -> T>(&self, f: F) -> JoinHandle<T::Output>
where
T: Future + Send + 'static,
T::Output: Send + 'static,
{
let tracker = self.task();
tokio::task::spawn(f(tracker))
}
/// Notify all tasks created by this TaskSpawner that they should abort.
pub fn cancel(&self) {
self.token.cancel();
}
}
impl TaskWaiter {
/// Notify all tasks this TaskWaiter is waiting on that they should abort.
pub fn cancel(&self) {
self.token.cancel();
}
/// Wait for the application to be interrupted, and then gracefully shutdown
/// allowing a timeout for all tasks to quit. A second interrupt will cause
/// an immediate shutdown.
///
/// On Unix systems, "interrupt" means a SIGINT or SIGTERM. On all other
/// platforms the current implementation uses `tokio::signal::ctrl_c()`
/// to wait for an interrupt.
pub async fn wait_for_shutdown(self, timeout: Duration) -> Result<(), Error> {
// Wait for the ctrl-c.
match wait_for_shutdown_signal().await {
Ok(()) => {
// time to shut down...
}
Err(_) => return Err(Error::CouldNotBindInterrupt),
}
// Let tasks know they should shut down.
self.token.cancel();
// Wait for everything to finish.
select! {
res = self.wait_with_timeout(timeout) => res,
_ = wait_for_shutdown_signal() => Err(Error::ShutdownEarly),
}
}
/// Wait for all tasks to finish. If tasks do not finish before the timeout,
/// `Error::Timeout` will be returned.
pub async fn wait_with_timeout(self, timeout: Duration) -> Result<(), Error> {
// Wait for all tasks to be dropped.
tokio::time::timeout(timeout, self.wait())
.await
.map_err(|_| Error::Timeout {})?;
Ok(())
}
/// Wait for all tasks to finish.
pub async fn wait(mut self) {
// Drop the tx half of the channel.
drop(self.stop_tx.lock().unwrap().take());
// Wait for all tasks to be dropped.
let _ = self.stop_rx.recv().await;
}
}
impl TaskTracker {
/// Create a new subtask from this TaskTracker.
pub fn subtask(&self) -> Self {
self.clone()
}
/// Spawn a subtask.
///
/// The given closure will be called, passing in a task tracker.
pub fn spawn<T, F: FnOnce(TaskTracker) -> T>(&self, f: F) -> JoinHandle<T::Output>
where
T: Future + Send + 'static,
T::Output: Send + 'static,
{
let tracker = self.subtask();
tokio::task::spawn(f(tracker))
}
/// Check to see if this task has been cancelled.
pub async fn cancelled(&self) {
self.token.cancelled().await;
}
/// Returns true if this token has been cancelled.
pub fn is_cancelled(&self) -> bool {
self.token.is_cancelled()
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::{
sync::atomic::{AtomicBool, Ordering},
time::Duration,
};
#[tokio::test]
async fn tracker_should_be_cancelled() {
let (spawner, waiter) = super::new();
let task = spawner.task();
waiter.cancel();
assert!(task.is_cancelled());
}
#[tokio::test]
async fn should_work_with_existing_cancellation_token() {
let token = CancellationToken::new();
let (spawner, _) = super::Builder::new()
.set_cancellation_token(token.clone())
.build();
let task = spawner.task();
// Cancelling the token should cancel the task.
token.cancel();
assert!(task.is_cancelled());
}
#[tokio::test]
async fn should_wait_for_tasks_to_complete() -> Result<(), Box<dyn std::error::Error>> {
let (spawner, waiter) = super::new();
let done = Arc::new(AtomicBool::new(false));
// Start a task
{
let done = done.clone();
spawner.spawn(|tracker| async move {
tokio::select! {
_ = tracker.cancelled() => {
// The token was cancelled, task should shut down.
}
_ = tokio::time::sleep(Duration::from_millis(100)) => {
// Short task has completed.
done.store(true, Ordering::SeqCst);
}
}
});
}
// Wait for all tasks to complete.
waiter.wait().await;
// Should have completed.
assert!(done.load(Ordering::SeqCst));
Ok(())
}
#[tokio::test]
async fn should_cancel_tasks() -> Result<(), Box<dyn std::error::Error>> {
let (spawner, waiter) = super::new();
let done = Arc::new(AtomicBool::new(false));
// Start a task
{
let done = done.clone();
spawner.spawn(|tracker| async move {
tokio::select! {
_ = tracker.cancelled() => {
// The token was cancelled, task should shut down.
}
_ = tokio::time::sleep(Duration::from_secs(9999)) => {
// Long work has completed
done.store(true, Ordering::SeqCst);
}
}
});
}
// Cancel the task after a short while.
tokio::time::sleep(Duration::from_millis(100)).await;
waiter.cancel();
// Wait for all tasks to complete.
waiter.wait().await;
// Should have timed out.
assert!(!done.load(Ordering::SeqCst));
Ok(())
}
#[tokio::test]
async fn interrupt_tests() -> Result<(), Box<dyn std::error::Error>> {
// Interrupt tests rely on global state in shutdown.rs to simulate
// SIGINT. Need to run these serially.
should_wait_for_tasks_on_interrupt().await?;
should_stop_immediately_on_second_interrupt().await?;
Ok(())
}
async fn should_wait_for_tasks_on_interrupt() -> Result<(), Box<dyn std::error::Error>> {
shutdown::reset_before_test();
let (spawner, waiter) = super::new();
let done = Arc::new(AtomicBool::new(false));
// Start a task
{
let done = done.clone();
spawner.spawn(|tracker| async move {
tokio::select! {
_ = tracker.cancelled() => {
// The token was cancelled, task should shut down.
}
_ = tokio::time::sleep(Duration::from_secs(9999)) => {
// Long running task...
done.store(true, Ordering::SeqCst);
}
}
});
}
// Send a fake shutdown signal.
tokio::spawn(async {
shutdown::send_shutdown().await;
});
// Wait for all tasks to complete.
waiter.wait_for_shutdown(Duration::from_secs(10)).await?;
// Task should have been aborted.
assert!(!done.load(Ordering::SeqCst));
Ok(())
}
async fn should_stop_immediately_on_second_interrupt() -> Result<(), Box<dyn std::error::Error>>
{
shutdown::reset_before_test();
let (spawner, waiter) = super::new();
let done = Arc::new(AtomicBool::new(false));
// Start a task
{
let done = done.clone();
spawner.spawn(|tracker| async move {
let _tracker = tracker;
// Long running task that can't be cancelled.
tokio::time::sleep(Duration::from_secs(99)).await;
done.store(true, Ordering::SeqCst);
});
}
// Send two shutdown signals. The second should cause us to die immediately.
tokio::spawn(async move {
shutdown::send_shutdown().await;
shutdown::send_shutdown().await;
});
// We shouldn't wait here, because of the second interrupt.
let err = waiter
.wait_for_shutdown(Duration::from_secs(99))
.await
.unwrap_err();
assert_eq!(err, Error::ShutdownEarly);
// Task should have been aborted.
assert!(!done.load(Ordering::SeqCst));
Ok(())
}
}