ntex_rt/

system.rs

use std::any::{Any, TypeId};
use std::collections::VecDeque;
use std::sync::{Arc, atomic::AtomicBool, atomic::AtomicUsize, atomic::Ordering};
use std::time::{Duration, Instant};
use std::{cell::RefCell, fmt, future::Future, pin::Pin};

use async_channel::{Receiver, Sender, unbounded};
use futures_timer::Delay;
use parking_lot::{Mutex, RwLock};

use crate::arbiter::Arbiter;
use crate::pool::{PoolMetrics, ThreadPool};
use crate::{BlockingResult, Builder, Handle, HashMap, Runner, SystemRunner, TaskCallbacks};

static SYSTEM_COUNT: AtomicUsize = AtomicUsize::new(0);

thread_local!(
    static PINGS: RefCell<HashMap<Id, VecDeque<PingRecord>>> = RefCell::new(HashMap::default());
);

#[derive(Default)]
struct Arbiters {
    all: HashMap<Id, Arbiter>,
    list: Vec<Arbiter>,
}

/// Identifier assigned to a [`System`] or [`Arbiter`].
///
/// System and arbiter identifiers use separate sequences.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
pub struct Id(pub(crate) usize);

/// Runtime manager for a group of arbiter threads.
///
/// A system stores runtime configuration, manages arbiters, dispatches process
/// signals, and owns the blocking thread pool.
///
/// Clones share the same system and may be sent to other threads. Merely holding
/// a handle does not install that system as the current system on another thread.
pub struct System(pub(crate) Arc<SystemInner>);

pub(crate) struct SystemInner {
    id: usize,
    arbiter: Arbiter,
    pub(crate) config: SystemConfig,
    sender: Sender<SystemCommand>,
    receiver: Receiver<SystemCommand>,
    storage: RwLock<HashMap<TypeId, Box<dyn Any + Sync + Send>>>,
    arbiters: Mutex<Arbiters>,
    signals: AtomicBool,
    pool: ThreadPool,
}

/// Configuration shared by a running [`System`].
///
/// Obtain a clone with [`System::config`] and reuse it with
/// [`System::with_config`] or [`Builder::build_with`]. Signal and panic-handling
/// settings are not part of this configuration.
#[derive(Clone)]
pub struct SystemConfig {
    pub(super) name: String,
    pub(super) stack_size: usize,
    pub(super) ping_interval: usize,
    pub(super) ping_threshold: usize,
    pub(super) latency_interval: usize,
    pub(super) pool_limit: usize,
    pub(super) pool_recv_timeout: Duration,
    pub(super) timer_resolution: u8,
    pub(super) testing: bool,
    pub(super) task_callbacks: Option<fn() -> TaskCallbacks>,
    pub(super) runner: Arc<dyn Runner>,
}

thread_local!(
    static CURRENT: RefCell<Option<System>> = const { RefCell::new(None) };
);

impl Clone for System {
    fn clone(&self) -> Self {
        Self(self.0.clone())
    }
}

impl SystemInner {
    /// Returns the registered arbiters.
    pub(crate) fn arbiters(&self) -> Vec<Arbiter> {
        self.arbiters.lock().list.clone()
    }
}

impl System {
    /// Constructs new system and sets it as current
    pub(super) fn start(config: SystemConfig) -> (Self, oneshot::Receiver<i32>) {
        let id = SYSTEM_COUNT.fetch_add(1, Ordering::SeqCst);
        let (sender, receiver) = unbounded();

        let pool = ThreadPool::new(&config.name, config.pool_limit, config.pool_recv_timeout);
        let (arbiter, controller) = Arbiter::new_system(id, config.name.clone());

        let mut arbiters = Arbiters::default();
        arbiters.all.insert(arbiter.id(), arbiter.clone());
        arbiters.list.push(arbiter.clone());

        let sys = System(Arc::new(SystemInner {
            id,
            config,
            arbiter,
            sender,
            receiver,
            pool,
            arbiters: Mutex::new(arbiters),
            storage: RwLock::new(HashMap::default()),
            signals: AtomicBool::new(false),
        }));
        System::set_current(sys.clone());

        let (stop_tx, stop) = oneshot::channel();

        // system support tasks
        crate::spawn_detached(SystemSupport::new(&sys, stop_tx).run());
        crate::spawn_detached(controller.run(sys.clone()));

        (sys, stop)
    }

    /// Creates a builder for a system with a customized runtime.
    ///
    /// See [`Builder`] for the available configuration options.
    pub fn build() -> Builder {
        Builder::new()
    }

    #[allow(clippy::new_ret_no_self)]
    /// Creates a system runner with the specified name and runtime runner.
    ///
    /// The system is not started until the returned runner is driven.
    pub fn new<R: Runner>(name: &str, runner: R) -> SystemRunner {
        Self::build().name(name).build(runner)
    }

    #[allow(clippy::new_ret_no_self)]
    /// Creates a system runner from an existing configuration.
    ///
    /// Replaces the configuration's name with `name`. Signal and panic handling
    /// are disabled for the new runner. The system starts only when it is driven.
    pub fn with_config(name: &str, mut config: SystemConfig) -> SystemRunner {
        name.clone_into(&mut config.name);
        Self::build().name(name).build_with(config)
    }

    /// Returns the system running on the current thread.
    ///
    /// # Panics
    ///
    /// Panics if no system is running on the current thread.
    pub fn current() -> System {
        CURRENT.with(|cell| match *cell.borrow() {
            Some(ref sys) => sys.clone(),
            None => panic!("System is not running"),
        })
    }

    /// Returns the system running on the current thread, if one exists.
    pub fn try_current() -> Option<System> {
        CURRENT.with(|cell| cell.borrow().as_ref().map(Clone::clone))
    }

    /// Set current running system
    #[doc(hidden)]
    pub fn set_current(sys: System) {
        crate::task::set_callbacks(sys.0.config.task_callbacks.map(|f| f()));
        CURRENT.with(|s| {
            *s.borrow_mut() = Some(sys);
        });
    }

    pub(crate) fn register_arbiter(&self, arb: Arbiter) {
        crate::task::set_callbacks(self.0.config.task_callbacks.map(|f| f()));
        CURRENT.with(|s| {
            *s.borrow_mut() = Some(self.clone());
        });
        let mut arbiters = self.0.arbiters.lock();
        arbiters.all.insert(arb.id(), arb.clone());
        arbiters.list.push(arb);
    }

    pub(crate) fn unregister_arbiter(&self, id: Id) {
        crate::task::set_callbacks(None);
        CURRENT.with(|s| {
            *s.borrow_mut() = None;
        });
        let mut arbiters = self.0.arbiters.lock();
        if let Some(hnd) = arbiters.all.remove(&id) {
            for (idx, arb) in arbiters.list.iter().enumerate() {
                if &hnd == arb {
                    arbiters.list.remove(idx);
                    break;
                }
            }
        }
    }

    pub(super) fn remove_current() {
        crate::task::set_callbacks(None);
        CURRENT.with(|cell| {
            cell.borrow_mut().take();
        });
    }

    /// Unregisters all arbiters of the system.
    pub(super) fn take_arbiters(&self) -> Vec<Arbiter> {
        let mut arbiters = self.0.arbiters.lock();
        arbiters.all.clear();
        std::mem::take(&mut arbiters.list)
    }

    /// Stops and unregisters all arbiters of the system.
    pub(super) fn stop_arbiters(&self) {
        for arb in self.take_arbiters() {
            arb.stop();
        }
    }

    /// Returns the system identifier.
    pub fn id(&self) -> Id {
        Id(self.0.id)
    }

    /// Returns the system name.
    pub fn name(&self) -> &str {
        &self.0.config.name
    }

    /// Requests that the system stop with exit code `0`.
    ///
    /// This does not wait for shutdown. See [`stop_with_code`](Self::stop_with_code).
    pub fn stop(&self) {
        self.stop_with_code(0);
    }

    /// Requests that the system stop with the specified exit code.
    ///
    /// The request is processed asynchronously on the primary arbiter, which
    /// asks all registered arbiters to stop. [`SystemRunner::run`] reports
    /// nonzero codes as errors. A runner awaiting a user future with
    /// [`SystemRunner::block_on`] still waits for that future to complete.
    pub fn stop_with_code(&self, code: i32) {
        let _ = self.0.sender.try_send(SystemCommand::Exit(code));
    }

    /// Returns whether this system owns process signal handling.
    pub fn signals(&self) -> bool {
        self.0.signals.load(Ordering::Relaxed)
    }

    /// Enables process signal handling.
    ///
    /// Signals are handled by one system at a time, this has no effect while
    /// another system handles signals. Call this on the system's primary
    /// arbiter thread, where its signal-delivery task and shutdown state live.
    pub fn enable_signals(&self) {
        if !self.signals() && crate::signals::start(self) {
            self.0.signals.store(true, Ordering::Relaxed);
        }
    }

    /// Disables process signal handling.
    pub fn disable_signals(&self) {
        if self.signals() {
            crate::signals::stop(self);
            self.0.signals.store(false, Ordering::Relaxed);
        }
    }

    /// Returns the system's primary arbiter.
    pub fn arbiter(&self) -> Arbiter {
        self.0.arbiter.clone()
    }

    /// Provides access to all arbiters registered with this system.
    ///
    /// The callback receives a snapshot, including the primary arbiter while it
    /// remains registered. It runs without the registry lock held, so it may
    /// create, stop, join, or enumerate arbiters. This method may be called from
    /// any thread.
    pub fn list_arbiters<F, R>(&self, f: F) -> R
    where
        F: FnOnce(&[Arbiter]) -> R,
    {
        f(&self.0.arbiters())
    }

    /// Visits the latest ping records for each registered arbiter.
    ///
    /// This method should be called from the thread where the system has been initialized,
    /// typically the "main" thread, because records are thread-local. Records
    /// are stored newest first, with at most ten per arbiter before callbacks
    /// modify them. Arbiters without records are not visited.
    ///
    /// The callback may modify the stored records and runs without the arbiter
    /// registry lock, but must not call this method recursively.
    ///
    /// # Panics
    ///
    /// Panics if no current system is installed or if called recursively.
    pub fn list_arbiter_pings<F>(mut f: F)
    where
        F: FnMut(&Arbiter, &mut VecDeque<PingRecord>),
    {
        PINGS.with(|pings| {
            let mut p = pings.borrow_mut();
            let sys = System::current();
            let arbiters: Vec<_> = {
                let arbiters = sys.0.arbiters.lock();
                p.keys()
                    .filter_map(|id| arbiters.all.get(id).map(|arb| (*id, arb.clone())))
                    .collect()
            };

            // callbacks run without the registry lock
            for (id, arb) in &arbiters {
                if let Some(recs) = p.get_mut(id) {
                    f(arb, recs);
                }
            }
        });
    }

    #[doc(hidden)]
    /// Set arbiter latency callback.
    ///
    /// This callback is called with the backtrace of a stalled arbiter, see
    /// [`Builder::ping_threshold`]. Backtraces are captured on Linux and
    /// Windows. The provided backtrace is not resolved. The location is the
    /// spawn location of the task that blocks the arbiter, see
    /// [`Handle::current_task`].
    pub fn set_latency_callback<F>(f: F)
    where
        F: Fn(ntex_error::Backtrace, Option<&'static std::panic::Location<'static>>)
            + Send
            + Sync
            + 'static,
    {
        crate::watchdog::set_latency_callback(Arc::new(f));
    }

    /// Returns a clone of the system configuration.
    pub fn config(&self) -> SystemConfig {
        self.0.config.clone()
    }

    #[inline]
    /// Returns a runtime handle for the primary arbiter.
    pub fn handle(&self) -> Handle {
        self.arbiter().handle().clone()
    }

    /// Returns whether the system is configured for testing.
    pub fn testing(&self) -> bool {
        self.0.config.testing()
    }

    #[inline]
    /// Returns the timer wheel resolution in milliseconds.
    ///
    /// See [`Builder::timer_resolution`].
    pub fn timer_resolution(&self) -> u8 {
        self.0.config.timer_resolution()
    }

    /// Submits blocking work to this system's thread pool and returns its result future.
    ///
    /// This method does not wait for completion. It may be called from any
    /// thread, regardless of which system is current there.
    ///
    /// Dropping the returned future prevents queued work from starting, but
    /// cannot interrupt work that is already running. Call
    /// [`BlockingResult::detach`] to let queued work continue even if its
    /// result is no longer needed.
    pub fn spawn_blocking<F, R>(&self, f: F) -> BlockingResult<R>
    where
        F: FnOnce() -> R + Send + 'static,
        R: Send + 'static,
    {
        self.0.pool.execute(f)
    }

    /// Returns a snapshot of the blocking thread pool metrics.
    pub fn pool_metrics(&self) -> PoolMetrics {
        self.0.pool.metrics()
    }

    /// Returns a clone of the system-wide value of type `T`, inserting one if absent.
    ///
    /// This method acquires a lock on the internal data structure.
    /// To avoid repeated locking, prefer storing a cloned value in the arbiter's storage.
    /// Initialization is not atomic: concurrent callers may each run `f` and
    /// return different values, with the last inserted clone remaining in storage.
    pub fn get_value<T>(&self, f: impl FnOnce() -> T) -> T
    where
        T: Clone + Send + Sync + 'static,
    {
        if let Some(boxed) = self.0.storage.read().get(&TypeId::of::<T>())
            && let Some(val) = (&**boxed as &(dyn Any + 'static)).downcast_ref::<T>()
        {
            val.clone()
        } else {
            let val = f();
            self.0
                .storage
                .write()
                .insert(TypeId::of::<T>(), Box::new(val.clone()));
            val
        }
    }
}

impl SystemConfig {
    #[inline]
    /// Returns whether the system is configured for testing.
    pub fn testing(&self) -> bool {
        self.testing
    }

    #[inline]
    /// Returns the timer wheel resolution in milliseconds.
    ///
    /// See [`Builder::timer_resolution`].
    pub fn timer_resolution(&self) -> u8 {
        self.timer_resolution
    }

    #[inline]
    /// Returns the task callbacks factory, if set.
    ///
    /// See [`Builder::task_callbacks`].
    pub fn task_callbacks(&self) -> Option<fn() -> TaskCallbacks> {
        self.task_callbacks
    }
}

impl fmt::Debug for System {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("System")
            .field("id", &self.0.id)
            .field("config", &self.0.config)
            .field("signals", &self.signals())
            .field("pool", &self.0.pool)
            .finish()
    }
}

impl fmt::Debug for SystemConfig {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("SystemConfig")
            .field("name", &self.name)
            .field("testing", &self.testing)
            .field("stack_size", &self.stack_size)
            .field("timer_resolution", &self.timer_resolution)
            .field("task_callbacks", &self.task_callbacks)
            .finish()
    }
}

#[derive(Debug)]
pub(super) enum SystemCommand {
    Exit(i32),
}

#[derive(Debug)]
struct SystemSupport {
    sys: System,
    stop: Option<oneshot::Sender<i32>>,
    commands: Receiver<SystemCommand>,
    watchdog: Option<Arc<AtomicBool>>,
}

impl Drop for SystemSupport {
    fn drop(&mut self) {
        self.stop_watchdog();
    }
}

impl SystemSupport {
    fn new(sys: &System, stop: oneshot::Sender<i32>) -> Self {
        Self {
            sys: sys.clone(),
            stop: Some(stop),
            commands: sys.0.receiver.clone(),
            watchdog: None,
        }
    }

    fn stop_watchdog(&mut self) {
        if let Some(stop) = self.watchdog.take() {
            stop.store(true, Ordering::Relaxed);
        }
    }

    async fn run(mut self) {
        crate::metrics::start_latency_sampler(
            &self.sys.0.arbiter.0.latency,
            self.sys.0.config.latency_interval,
        );
        self.watchdog = crate::watchdog::start(&self.sys);
        if self.sys.0.config.ping_interval != 0 {
            crate::spawn_detached(ping_arbiters(self.sys.clone()));
        }

        loop {
            match self.commands.recv().await {
                Ok(SystemCommand::Exit(code)) => {
                    log::debug!("Stopping system with {code} code");
                    self.stop_watchdog();
                    self.sys.stop_arbiters();

                    crate::arbiter::run_shutdown_callbacks();

                    // stop event loop
                    if let Some(stop) = self.stop.take() {
                        let _ = stop.send(code);
                    }
                }
                Err(_) => {
                    log::debug!("System stopped");
                    return;
                }
            }
        }
    }
}

/// A ping sent to an arbiter, as exposed by [`System::list_arbiter_pings`].
#[derive(Copy, Clone, Debug)]
pub struct PingRecord {
    /// Time the ping round started.
    pub start: Instant,
    /// Elapsed time when the primary arbiter observed the ping task complete.
    ///
    /// `None` means no successful response has been recorded, including when
    /// the ping is still pending or its task was canceled.
    pub rtt: Option<Duration>,
}

async fn ping_arbiters(sys: System) {
    let interval = Duration::from_millis(sys.0.config.ping_interval as u64);

    loop {
        // interval between pings
        Delay::new(interval).await;

        let start = Instant::now();
        let arbiters = sys.0.arbiters.lock();

        // drop records of stopped arbiters
        PINGS.with(|pings| {
            pings
                .borrow_mut()
                .retain(|id, _| arbiters.all.contains_key(id));
        });

        for arb in &arbiters.list {
            let id = arb.id();
            let fut = arb.handle().spawn(async move {
                yield_to().await;
            });

            PINGS.with(|pings| {
                let mut p = pings.borrow_mut();
                let recs = p.entry(id).or_default();
                recs.push_front(PingRecord { start, rtt: None });
                recs.truncate(10);
            });

            crate::spawn_detached(async move {
                if fut.await.is_ok() {
                    PINGS.with(|pings| {
                        // a late pong belongs to its own round
                        if let Some(recs) = pings.borrow_mut().get_mut(&id)
                            && let Some(rec) = recs.iter_mut().find(|r| r.start == start)
                        {
                            rec.rtt = Some(start.elapsed());
                        }
                    });
                }
            });
        }
    }
}

async fn yield_to() {
    use std::task::{Context, Poll};

    struct Yield {
        completed: bool,
    }

    impl Future for Yield {
        type Output = ();

        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
            if self.completed {
                return Poll::Ready(());
            }
            self.completed = true;
            cx.waker().wake_by_ref();
            Poll::Pending
        }
    }

    Yield { completed: false }.await;
}

#[cfg(test)]
#[path = "../tests/unit/system.rs"]
mod tests;