near-async 0.35.1

use crate::instrumentation::queue::InstrumentedQueue;
use crate::instrumentation::writer::InstrumentedThreadWriterSharedPart;
use crate::messaging::Actor;
use crate::pretty_type_name;
use std::sync::Arc;
use std::thread;
use std::time::Duration;

/// MultithreadRuntimeMessage is a type alias for a boxed function that can be sent to the multithread runtime,
/// as well as a description for debugging purposes.
pub(super) struct MultithreadRuntimeMessage<A> {
    pub(super) seq: u64,
    pub(super) enqueued_time_ns: u64,
    pub(super) name: &'static str,
    pub(super) function: Box<dyn FnOnce(&mut A) + Send>,
}

/// Allows sending messages to a multithreaded actor runtime. Implements CanSend and CanSendAsync traits
/// for the messages that the actor can handle.
pub struct MultithreadRuntimeHandle<A> {
    pub(super) sender: crossbeam_channel::Sender<MultithreadRuntimeMessage<A>>,
    /// This is used in the case where the handle controls the lifetime of the runtime,
    /// dropping (all of) which automatically stops the runtime, as an alterative of having
    /// the ActorSystem control it.
    cancellation_signal_holder: Option<crossbeam_channel::Sender<()>>,
    pub(super) instrumentation: Arc<InstrumentedThreadWriterSharedPart>,
}

impl<A> Clone for MultithreadRuntimeHandle<A> {
    fn clone(&self) -> Self {
        Self {
            sender: self.sender.clone(),
            cancellation_signal_holder: self.cancellation_signal_holder.clone(),
            instrumentation: self.instrumentation.clone(),
        }
    }
}

impl<A> MultithreadRuntimeHandle<A>
where
    A: 'static,
{
    pub fn sender(&self) -> Arc<MultithreadRuntimeHandle<A>> {
        Arc::new(self.clone())
    }
}

impl<A> MultithreadRuntimeHandle<A> {
    pub(super) fn send_message(
        &self,
        message: MultithreadRuntimeMessage<A>,
    ) -> Result<(), crossbeam_channel::SendError<MultithreadRuntimeMessage<A>>> {
        let name = message.name;
        self.sender.send(message).map(|_| {
            // Only increment the queue if the message was successfully sent.
            self.instrumentation.queue().enqueue(name);
        })
    }
}

/// See ActorSystem::spawn_multithread_actor.
///
/// The `cancellation_signal_holder` is an optional sender that can be used to disable
/// system-wide cancellation. If this sender is used, it is just the other side of the
/// `cancellation_signal`.
pub(crate) fn spawn_multithread_actor<A>(
    num_threads: usize,
    make_actor_fn: impl Fn() -> A + Sync + Send + 'static,
    cancellation_signal: crossbeam_channel::Receiver<()>,
    cancellation_signal_holder: Option<crossbeam_channel::Sender<()>>,
) -> MultithreadRuntimeHandle<A>
where
    A: Actor + Send + 'static,
{
    let actor_name = pretty_type_name::<A>();
    tracing::debug!(
        target: "multithread_runtime",
        actor_name,
        num_threads,
        "starting multithread actor",
    );
    let (sender, receiver) = crossbeam_channel::unbounded::<MultithreadRuntimeMessage<A>>();
    let instrumented_queue = InstrumentedQueue::new(actor_name);
    let shared_instrumentation =
        InstrumentedThreadWriterSharedPart::new(actor_name.to_string(), instrumented_queue.clone());
    let handle = MultithreadRuntimeHandle {
        sender,
        cancellation_signal_holder,
        instrumentation: shared_instrumentation,
    };
    let make_actor_fn = Arc::new(make_actor_fn);

    // Spawn num_threads OS-level threads
    for thread_id in 0..num_threads {
        let receiver = receiver.clone();
        let cancellation_signal = cancellation_signal.clone();
        let instrumented_queue = instrumented_queue.clone();
        let handle = handle.clone();
        let make_actor_fn = make_actor_fn.clone();

        thread::spawn(move || {
            let mut instrumentation =
                handle.instrumentation.new_writer_with_global_registration(Some(thread_id));
            let mut actor = make_actor_fn();
            let window_update_ticker = crossbeam_channel::tick(Duration::from_secs(1));
            loop {
                crossbeam_channel::select! {
                    recv(cancellation_signal) -> _ => {
                        tracing::info!(target: "multithread_runtime", actor_name, thread_id, "cancellation received, exiting loop");
                        return;
                    }
                    recv(window_update_ticker) -> _ => {
                        tracing::trace!(target: "multithread_runtime", actor_name, thread_id, "updating instrumentation window");
                        instrumentation.advance_window_if_needed();
                    }
                    recv(receiver) -> message => {
                        let Ok(message) = message else {
                            tracing::warn!(target: "multithread_runtime", actor_name, thread_id, "message queue closed, exiting event loop");
                            return;
                        };
                        instrumented_queue.dequeue(message.name);
                        let seq = message.seq;
                        let dequeue_time_ns = handle.instrumentation.current_time().saturating_sub(message.enqueued_time_ns);
                        instrumentation.start_event(message.name, dequeue_time_ns);
                        tracing::trace!(target: "multithread_runtime", seq, "executing message");
                        (message.function)(&mut actor);
                        instrumentation.end_event(message.name);
                    }
                }
            }
        });
    }
    handle
}