serf-core 0.5.1

A decentralized solution for service discovery and orchestration that is lightweight, highly available, and fault tolerant.
Documentation 
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mod member;
pub(crate) use member::*;
mod user;
pub(crate) use user::*;

use std::{future::Future, time::Duration};

use async_channel::{Receiver, Sender, bounded};
use futures::FutureExt;
use memberlist_core::{
  agnostic_lite::RuntimeLite,
  tracing,
  transport::{AddressResolver, Transport},
};

use crate::delegate::Delegate;

use super::event::CrateEvent;

pub(crate) struct ClosedOutChannel;

pub(crate) trait Coalescer: Send + Sync + 'static {
  type Delegate: Delegate<
      Id = <Self::Transport as Transport>::Id,
      Address = <<Self::Transport as Transport>::Resolver as AddressResolver>::ResolvedAddress,
    >;
  type Transport: Transport;

  fn name(&self) -> &'static str;

  fn handle(&self, event: &CrateEvent<Self::Transport, Self::Delegate>) -> bool;

  /// Invoked to coalesce the given event
  fn coalesce(&mut self, event: CrateEvent<Self::Transport, Self::Delegate>);

  /// Invoked to flush the coalesced events
  fn flush(
    &mut self,
    out_tx: &Sender<CrateEvent<Self::Transport, Self::Delegate>>,
  ) -> impl Future<Output = Result<(), ClosedOutChannel>> + Send;
}

/// Returns an event channel where the events are coalesced
/// using the given coalescer.
pub(crate) fn coalesced_event<C: Coalescer>(
  out_tx: Sender<CrateEvent<C::Transport, C::Delegate>>,
  shutdown_rx: Receiver<()>,
  c_period: Duration,
  q_period: Duration,
  c: C,
) -> Sender<CrateEvent<C::Transport, C::Delegate>> {
  let (in_tx, in_rx) = bounded(1024);
  <<C::Transport as Transport>::Runtime as RuntimeLite>::spawn_detach(coalesce_loop::<C>(
    in_rx,
    out_tx,
    shutdown_rx,
    c_period,
    q_period,
    c,
  ));
  in_tx
}

/// A simple long-running routine that manages the high-level
/// flow of coalescing based on quiescence and a maximum quantum period.
async fn coalesce_loop<C: Coalescer>(
  in_rx: Receiver<CrateEvent<C::Transport, C::Delegate>>,
  out_tx: Sender<CrateEvent<C::Transport, C::Delegate>>,
  shutdown_rx: Receiver<()>,
  coalesce_peirod: Duration,
  quiescent_period: Duration,
  mut c: C,
) {
  let mut quiescent = None;
  let mut quantum = None;
  let mut shutdown = false;

  loop {
    futures::select! {
      ev = in_rx.recv().fuse() => {
        let Ok(ev) = ev else {
          // if we receive an error, it means the channel is closed. We should return
          return;
        };

        // Ignore any non handled events
        if !c.handle(&ev) {
          if let Err(e) = out_tx.send(ev).await {
            tracing::error!(err=%e, "serf: fail send event to out channel in {} coalesce thread", c.name());
            return;
          }
          continue;
        }

        // Start a new quantum if we need to
        // and restart the quiescent timer
        if quantum.is_none() {
          quantum = Some(<<C::Transport as Transport>::Runtime as RuntimeLite>::sleep(coalesce_peirod));
        }
        quiescent = Some(<<C::Transport as Transport>::Runtime as RuntimeLite>::sleep(quiescent_period));

        // Coalesce the event
        c.coalesce(ev);
      }
      _ = async {
        if let Some(quantum) = quantum.take() {
          quantum.await;

        } else {
          std::future::pending::<()>().await;
        }
      }.fuse() => {
        // Flush the coalesced events
        if c.flush(&out_tx).await.is_err() {
          tracing::error!(err="closed channel", "serf: fail send event to out channel in {} coalesce thread", c.name());
          return;
        }

        // Restart ingestion if we are not done
        if !shutdown {
          quiescent = None;
          quantum = None;
          continue;
        }

        return;
      }
      _ = async {
        if let Some(quiescent) = quiescent.take() {
          quiescent.await;
        } else {
          std::future::pending::<()>().await;
        }
      }.fuse() => {
        // Flush the coalesced events
        if c.flush(&out_tx).await.is_err() {
          tracing::error!(err="closed channel", "serf: fail send event to out channel in {} coalesce thread", c.name());
          return;
        }

        // Restart ingestion if we are not done
        if !shutdown {
          quantum = None;
          quiescent = None;
          continue;
        }

        return;
      }
      _ = shutdown_rx.recv().fuse() => {
        shutdown = true;
      }
    }
  }
}