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feat: introduce
LeadershipChangeNotifier and `LeadershipChangeListe…
…ner` (#4817) * feat: introduce `LeadershipChangeNotifier` * refactor: use `LeadershipChangeNotifier` * chore: apply suggestions from CR * chore: apply suggestions from CR * chore: adjust log styling
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,156 @@ | ||
| // Copyright 2023 Greptime Team | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
|
||
| use std::sync::Arc; | ||
|
|
||
| use async_trait::async_trait; | ||
| use common_telemetry::error; | ||
|
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| use crate::error::Result; | ||
|
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| pub type LeadershipChangeNotifierCustomizerRef = Arc<dyn LeadershipChangeNotifierCustomizer>; | ||
|
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| /// A trait for customizing the leadership change notifier. | ||
| pub trait LeadershipChangeNotifierCustomizer: Send + Sync { | ||
| fn customize(&self, notifier: &mut LeadershipChangeNotifier); | ||
| } | ||
|
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| /// A trait for handling leadership change events in a distributed system. | ||
| #[async_trait] | ||
| pub trait LeadershipChangeListener: Send + Sync { | ||
| /// Returns the listener name. | ||
| fn name(&self) -> &str; | ||
|
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| /// Called when the node transitions to the leader role. | ||
| async fn on_leader_start(&self) -> Result<()>; | ||
|
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| /// Called when the node transitions to the follower role. | ||
| async fn on_leader_stop(&self) -> Result<()>; | ||
| } | ||
|
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| /// A notifier for leadership change events. | ||
| #[derive(Default)] | ||
| pub struct LeadershipChangeNotifier { | ||
| listeners: Vec<Arc<dyn LeadershipChangeListener>>, | ||
| } | ||
|
|
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| impl LeadershipChangeNotifier { | ||
| /// Adds a listener to the notifier. | ||
| pub fn add_listener(&mut self, listener: Arc<dyn LeadershipChangeListener>) { | ||
| self.listeners.push(listener); | ||
| } | ||
|
|
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| /// Notify all listeners that the node has become a leader. | ||
| pub async fn notify_on_leader_start(&self) { | ||
| for listener in &self.listeners { | ||
| if let Err(err) = listener.on_leader_start().await { | ||
| error!( | ||
| err; | ||
| "Failed to notify listener: {}, event 'on_leader_start'", | ||
| listener.name() | ||
| ); | ||
| } | ||
| } | ||
| } | ||
|
|
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| /// Notify all listeners that the node has become a follower. | ||
| pub async fn notify_on_leader_stop(&self) { | ||
| for listener in &self.listeners { | ||
| if let Err(err) = listener.on_leader_stop().await { | ||
| error!( | ||
| err; | ||
| "Failed to notify listener: {}, event: 'on_follower_start'", | ||
| listener.name() | ||
| ); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
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| #[cfg(test)] | ||
| mod tests { | ||
| use std::sync::atomic::{AtomicBool, Ordering}; | ||
| use std::sync::Arc; | ||
|
|
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| use super::*; | ||
|
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| struct MockListener { | ||
| name: String, | ||
| on_leader_start_fn: Option<Box<dyn Fn() -> Result<()> + Send + Sync>>, | ||
| on_follower_start_fn: Option<Box<dyn Fn() -> Result<()> + Send + Sync>>, | ||
| } | ||
|
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| #[async_trait::async_trait] | ||
| impl LeadershipChangeListener for MockListener { | ||
| fn name(&self) -> &str { | ||
| &self.name | ||
| } | ||
|
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| async fn on_leader_start(&self) -> Result<()> { | ||
| if let Some(f) = &self.on_leader_start_fn { | ||
| return f(); | ||
| } | ||
| Ok(()) | ||
| } | ||
|
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| async fn on_leader_stop(&self) -> Result<()> { | ||
| if let Some(f) = &self.on_follower_start_fn { | ||
| return f(); | ||
| } | ||
| Ok(()) | ||
| } | ||
| } | ||
|
|
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| #[tokio::test] | ||
| async fn test_leadership_change_notifier() { | ||
| let mut notifier = LeadershipChangeNotifier::default(); | ||
| let listener1 = Arc::new(MockListener { | ||
| name: "listener1".to_string(), | ||
| on_leader_start_fn: None, | ||
| on_follower_start_fn: None, | ||
| }); | ||
| let called_on_leader_start = Arc::new(AtomicBool::new(false)); | ||
| let called_on_follower_start = Arc::new(AtomicBool::new(false)); | ||
| let called_on_leader_start_moved = called_on_leader_start.clone(); | ||
| let called_on_follower_start_moved = called_on_follower_start.clone(); | ||
| let listener2 = Arc::new(MockListener { | ||
| name: "listener2".to_string(), | ||
| on_leader_start_fn: Some(Box::new(move || { | ||
| called_on_leader_start_moved.store(true, Ordering::Relaxed); | ||
| Ok(()) | ||
| })), | ||
| on_follower_start_fn: Some(Box::new(move || { | ||
| called_on_follower_start_moved.store(true, Ordering::Relaxed); | ||
| Ok(()) | ||
| })), | ||
| }); | ||
|
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| notifier.add_listener(listener1); | ||
| notifier.add_listener(listener2); | ||
|
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| let listener1 = notifier.listeners.first().unwrap(); | ||
| let listener2 = notifier.listeners.get(1).unwrap(); | ||
|
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| assert_eq!(listener1.name(), "listener1"); | ||
| assert_eq!(listener2.name(), "listener2"); | ||
|
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| notifier.notify_on_leader_start().await; | ||
| assert!(!called_on_follower_start.load(Ordering::Relaxed)); | ||
| assert!(called_on_leader_start.load(Ordering::Relaxed)); | ||
|
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| notifier.notify_on_leader_stop().await; | ||
| assert!(called_on_follower_start.load(Ordering::Relaxed)); | ||
| assert!(called_on_leader_start.load(Ordering::Relaxed)); | ||
| } | ||
| } |
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