[GitHub] [arrow-datafusion] yahoNanJing commented on a change in pull request #1912: Refactor the event channel

[GitBox <gi...@apache.org>]

yahoNanJing commented on a change in pull request #1912:
URL: https://github.com/apache/arrow-datafusion/pull/1912#discussion_r819974010



##########
File path: ballista/rust/core/src/event_loop.rs
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@@ -0,0 +1,128 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you 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::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+
+use async_trait::async_trait;
+use log::{error, info, warn};
+use tokio::sync::mpsc;
+
+use crate::error::{BallistaError, Result};
+
+#[async_trait]
+pub trait EventAction<E>: Send + Sync {
+    fn on_start(&self);
+
+    fn on_stop(&self);
+
+    async fn on_receive(&self, event: E) -> Result<Option<E>>;
+
+    fn on_error(&self, error: BallistaError);
+}
+
+pub struct EventLoop<E> {
+    name: String,
+    stopped: Arc<AtomicBool>,
+    buffer_size: usize,
+    action: Arc<dyn EventAction<E>>,
+    tx_event: Option<mpsc::Sender<E>>,
+}
+
+impl<E: Send + 'static> EventLoop<E> {
+    pub fn new(
+        name: String,
+        buffer_size: usize,
+        action: Arc<dyn EventAction<E>>,
+    ) -> Self {
+        Self {
+            name,
+            stopped: Arc::new(AtomicBool::new(false)),
+            buffer_size,
+            action,
+            tx_event: None,
+        }
+    }
+
+    fn run(&self, mut rx_event: mpsc::Receiver<E>) {
+        assert!(
+            self.tx_event.is_some(),
+            "The event sender should be initialized first!"
+        );
+        let tx_event = self.tx_event.as_ref().unwrap().clone();
+        let name = self.name.clone();
+        let stopped = self.stopped.clone();
+        let action = self.action.clone();
+        tokio::spawn(async move {
+            info!("Starting the event loop {}", name);
+            while !stopped.load(Ordering::SeqCst) {
+                let event = rx_event.recv().await.unwrap();

Review comment:
       Yes. In general, the channel won't be closed until the scheduler is down. The dangling task should be handled by another way, like speculative task execution.




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