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// Copyright (C) 2018-2020 Sebastian Dröge <sebastian@centricular.com>
// Copyright (C) 2019-2022 François Laignel <fengalin@free.fr>
//
// Take a look at the license at the top of the repository in the LICENSE file.
use futures::channel::oneshot;
use futures::pin_mut;
use gio::glib::clone::Downgrade;
use std::cell::RefCell;
use std::future::Future;
use std::panic;
#[cfg(feature = "tuning")]
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::mpsc as sync_mpsc;
use std::sync::{Arc, Condvar, Mutex, Weak};
use std::task::Poll;
use std::thread;
use std::time::{Duration, Instant};
use waker_fn::waker_fn;
use super::task::{SubTaskOutput, TaskId, TaskQueue};
use super::{CallOnDrop, JoinHandle, Reactor};
use crate::runtime::RUNTIME_CAT;
thread_local! {
static CURRENT_SCHEDULER: RefCell<Option<HandleWeak>> = RefCell::new(None);
}
#[derive(Debug)]
pub(super) struct Scheduler {
context_name: Arc<str>,
max_throttling: Duration,
tasks: TaskQueue,
must_unpark: Mutex<bool>,
must_unpark_cvar: Condvar,
#[cfg(feature = "tuning")]
parked_duration: AtomicU64,
}
impl Scheduler {
pub const DUMMY_NAME: &'static str = "DUMMY";
pub fn start(context_name: &str, max_throttling: Duration) -> Handle {
// Name the thread so that it appears in panic messages.
let thread = thread::Builder::new().name(context_name.to_string());
let (handle_sender, handle_receiver) = sync_mpsc::channel();
let (shutdown_sender, shutdown_receiver) = oneshot::channel();
let context_name = Arc::from(context_name);
let thread_ctx_name = Arc::clone(&context_name);
let join = thread
.spawn(move || {
gst::debug!(
RUNTIME_CAT,
"Started Scheduler thread for Context {}",
thread_ctx_name
);
let handle = Scheduler::init(Arc::clone(&thread_ctx_name), max_throttling);
let this = Arc::clone(&handle.0.scheduler);
handle_sender.send(handle.clone()).unwrap();
match this.block_on_priv(shutdown_receiver) {
Ok(_) => {
gst::debug!(
RUNTIME_CAT,
"Scheduler thread shut down for Context {}",
thread_ctx_name
);
}
Err(e) => {
gst::error!(
RUNTIME_CAT,
"Scheduler thread shut down due to an error within Context {}",
thread_ctx_name
);
// We are shutting down on our own initiative
if let Ok(mut shutdown) = handle.0.shutdown.lock() {
shutdown.clear();
}
panic::resume_unwind(e);
}
}
})
.expect("Failed to spawn Scheduler thread");
let handle = handle_receiver.recv().expect("Context thread init failed");
handle.set_shutdown(shutdown_sender, join);
handle
}
fn init(context_name: Arc<str>, max_throttling: Duration) -> Handle {
let handle = CURRENT_SCHEDULER.with(|cur_scheduler| {
let mut cur_scheduler = cur_scheduler.borrow_mut();
if cur_scheduler.is_some() {
panic!("Attempt to initialize an Scheduler on thread where another Scheduler is running.");
}
let handle = Handle::new(Arc::new(Scheduler {
context_name: context_name.clone(),
max_throttling,
tasks: TaskQueue::new(context_name),
must_unpark: Mutex::new(false),
must_unpark_cvar: Condvar::new(),
#[cfg(feature = "tuning")]
parked_duration: AtomicU64::new(0),
}));
*cur_scheduler = Some(handle.downgrade());
handle
});
Reactor::init(handle.max_throttling());
handle
}
pub fn block_on<F>(future: F) -> F::Output
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
assert!(
!Scheduler::is_scheduler_thread(),
"Attempt to block within an existing Scheduler thread."
);
let handle = Scheduler::init(Scheduler::DUMMY_NAME.into(), Duration::ZERO);
let this = Arc::clone(&handle.0.scheduler);
let (task_id, task) = this.tasks.add(async move {
let res = future.await;
let task_id = TaskId::current().unwrap();
let _ = handle.drain_sub_tasks(task_id).await;
res
});
gst::trace!(RUNTIME_CAT, "Blocking on current thread with {:?}", task_id);
let _guard = CallOnDrop::new(|| {
gst::trace!(
RUNTIME_CAT,
"Blocking on current thread with {:?} done",
task_id,
);
});
match this.block_on_priv(task) {
Ok(res) => res,
Err(e) => {
gst::error!(
RUNTIME_CAT,
"Panic blocking on Context {}",
&Scheduler::DUMMY_NAME
);
panic::resume_unwind(e);
}
}
}
fn block_on_priv<F>(&self, future: F) -> std::thread::Result<F::Output>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
let waker = waker_fn(|| ());
let cx = &mut std::task::Context::from_waker(&waker);
pin_mut!(future);
let _guard = CallOnDrop::new(|| Scheduler::close(Arc::clone(&self.context_name)));
if let Poll::Ready(t) = future.as_mut().poll(cx) {
return Ok(t);
}
let mut last;
loop {
last = Instant::now();
Reactor::with_mut(|reactor| reactor.react(last).ok());
if let Poll::Ready(t) = future.as_mut().poll(cx) {
return Ok(t);
}
while let Ok(runnable) = self.tasks.pop_runnable() {
panic::catch_unwind(|| runnable.run()).map_err(|err| {
gst::error!(
RUNTIME_CAT,
"A task has panicked within Context {}",
self.context_name
);
err
})?;
}
let mut must_unpark = self.must_unpark.lock().unwrap();
loop {
if *must_unpark {
*must_unpark = false;
break;
}
if let Some(parking_duration) = self.max_throttling.checked_sub(last.elapsed()) {
let result = self
.must_unpark_cvar
.wait_timeout(must_unpark, parking_duration)
.unwrap();
#[cfg(feature = "tuning")]
self.parked_duration
.fetch_add(parking_duration.subsec_nanos() as u64, Ordering::Relaxed);
must_unpark = result.0;
} else {
*must_unpark = false;
break;
}
}
}
}
fn unpark(&self) {
let mut must_unpark = self.must_unpark.lock().unwrap();
*must_unpark = true;
self.must_unpark_cvar.notify_one();
}
fn close(context_name: Arc<str>) {
gst::trace!(
RUNTIME_CAT,
"Closing Scheduler for Context {}",
context_name,
);
Reactor::close();
let _ = CURRENT_SCHEDULER.try_with(|cur_scheduler| {
*cur_scheduler.borrow_mut() = None;
});
}
pub fn is_scheduler_thread() -> bool {
CURRENT_SCHEDULER.with(|cur_scheduler| cur_scheduler.borrow().is_some())
}
pub fn current() -> Option<Handle> {
CURRENT_SCHEDULER.with(|cur_scheduler| {
cur_scheduler
.borrow()
.as_ref()
.and_then(HandleWeak::upgrade)
})
}
pub fn is_current(&self) -> bool {
CURRENT_SCHEDULER.with(|cur_scheduler| {
cur_scheduler
.borrow()
.as_ref()
.and_then(HandleWeak::upgrade)
.map_or(false, |cur| {
std::ptr::eq(self, Arc::as_ptr(&cur.0.scheduler))
})
})
}
}
impl Drop for Scheduler {
fn drop(&mut self) {
gst::debug!(
RUNTIME_CAT,
"Terminated: Scheduler for Context {}",
self.context_name
);
}
}
#[derive(Debug)]
struct SchedulerShutdown {
scheduler: Arc<Scheduler>,
sender: Option<oneshot::Sender<()>>,
join: Option<thread::JoinHandle<()>>,
}
impl SchedulerShutdown {
fn new(scheduler: Arc<Scheduler>) -> Self {
SchedulerShutdown {
scheduler,
sender: None,
join: None,
}
}
fn clear(&mut self) {
self.sender = None;
self.join = None;
}
}
impl Drop for SchedulerShutdown {
fn drop(&mut self) {
if let Some(sender) = self.sender.take() {
gst::debug!(
RUNTIME_CAT,
"Shutting down Scheduler thread for Context {}",
self.scheduler.context_name
);
drop(sender);
// Don't block shutting down itself
if !self.scheduler.is_current() {
if let Some(join_handler) = self.join.take() {
gst::trace!(
RUNTIME_CAT,
"Waiting for Scheduler thread to shutdown for Context {}",
self.scheduler.context_name
);
let _ = join_handler.join();
}
}
}
}
}
#[derive(Debug)]
struct HandleInner {
scheduler: Arc<Scheduler>,
shutdown: Mutex<SchedulerShutdown>,
}
#[derive(Clone, Debug)]
pub(super) struct HandleWeak(Weak<HandleInner>);
impl HandleWeak {
pub(super) fn upgrade(&self) -> Option<Handle> {
self.0.upgrade().map(Handle)
}
}
#[derive(Clone, Debug)]
pub(super) struct Handle(Arc<HandleInner>);
impl Handle {
fn new(scheduler: Arc<Scheduler>) -> Self {
Handle(Arc::new(HandleInner {
shutdown: Mutex::new(SchedulerShutdown::new(Arc::clone(&scheduler))),
scheduler,
}))
}
fn set_shutdown(&self, sender: oneshot::Sender<()>, join: thread::JoinHandle<()>) {
let mut shutdown = self.0.shutdown.lock().unwrap();
shutdown.sender = Some(sender);
shutdown.join = Some(join);
}
pub fn context_name(&self) -> &str {
&self.0.scheduler.context_name
}
pub fn max_throttling(&self) -> Duration {
self.0.scheduler.max_throttling
}
#[cfg(feature = "tuning")]
pub fn parked_duration(&self) -> Duration {
Duration::from_nanos(self.0.scheduler.parked_duration.load(Ordering::Relaxed))
}
/// Executes the provided function relatively to this [`Scheduler`]'s [`Reactor`].
///
/// Usefull to initialze i/o sources and timers from outside
/// of a [`Scheduler`].
///
/// # Panic
///
/// This will block current thread and would panic if run
/// from the [`Scheduler`].
pub fn enter<'a, F, O>(&'a self, f: F) -> O
where
F: FnOnce() -> O + Send + 'a,
O: Send + 'a,
{
assert!(!self.0.scheduler.is_current());
// Safety: bounding `self` to `'a` and blocking on the task
// ensures that the lifetime bounds satisfy the safety
// requirements for `TaskQueue::add_sync`.
let task = unsafe { self.0.scheduler.tasks.add_sync(f) };
self.0.scheduler.unpark();
futures::executor::block_on(task)
}
pub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
let (task_id, task) = self.0.scheduler.tasks.add(future);
JoinHandle::new(task_id, task, self)
}
pub fn spawn_and_unpark<F>(&self, future: F) -> JoinHandle<F::Output>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
let (task_id, task) = self.0.scheduler.tasks.add(future);
self.0.scheduler.unpark();
JoinHandle::new(task_id, task, self)
}
pub(super) fn unpark(&self) {
self.0.scheduler.unpark();
}
pub fn add_sub_task<T>(&self, task_id: TaskId, sub_task: T) -> Result<(), T>
where
T: Future<Output = SubTaskOutput> + Send + 'static,
{
self.0.scheduler.tasks.add_sub_task(task_id, sub_task)
}
pub fn downgrade(&self) -> HandleWeak {
HandleWeak(self.0.downgrade())
}
pub async fn drain_sub_tasks(&self, task_id: TaskId) -> SubTaskOutput {
let sub_tasks_fut = self.0.scheduler.tasks.drain_sub_tasks(task_id);
sub_tasks_fut.await
}
}
impl PartialEq for Handle {
fn eq(&self, other: &Self) -> bool {
Arc::ptr_eq(&self.0, &other.0)
}
}
#[cfg(test)]
mod tests {
use super::super::*;
use std::time::Duration;
#[test]
fn block_on_task_join_handle() {
use futures::channel::oneshot;
use std::sync::mpsc;
let (join_sender, join_receiver) = mpsc::channel();
let (shutdown_sender, shutdown_receiver) = oneshot::channel();
std::thread::spawn(move || {
let handle =
Scheduler::init("block_on_task_join_handle".into(), Duration::from_millis(2));
let join_handle = handle.spawn(async {
timer::delay_for(Duration::from_millis(5)).await;
42
});
let _ = join_sender.send(join_handle);
let _ = handle.0.scheduler.block_on_priv(shutdown_receiver);
});
let task_join_handle = join_receiver.recv().unwrap();
let res = Scheduler::block_on(task_join_handle).unwrap();
let _ = shutdown_sender.send(());
assert_eq!(res, 42);
}
#[test]
fn block_on_timer() {
let res = Scheduler::block_on(async {
timer::delay_for(Duration::from_millis(5)).await;
42
});
assert_eq!(res, 42);
}
#[test]
fn enter_non_static() {
let handle = Scheduler::start("enter_non_static", Duration::from_millis(2));
let mut flag = false;
handle.enter(|| flag = true);
assert!(flag);
}
}
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