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

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

thinkharderdev commented on a change in pull request #1912:
URL: https://github.com/apache/arrow-datafusion/pull/1912#discussion_r819833301



##########
File path: ballista/rust/core/src/event_loop.rs
##########
@@ -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:
       So I understand, if the channel is closed, this will panic and the task will die? 

##########
File path: ballista/rust/scheduler/src/scheduler_server/mod.rs
##########
@@ -0,0 +1,142 @@
+// 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::collections::HashMap;
+use std::sync::Arc;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use tokio::sync::RwLock;
+use tonic::transport::Channel;
+
+use ballista_core::config::{BallistaConfig, TaskSchedulingPolicy};
+use ballista_core::error::Result;
+use ballista_core::event_loop::EventLoop;
+use ballista_core::serde::protobuf::executor_grpc_client::ExecutorGrpcClient;
+
+use ballista_core::serde::{AsExecutionPlan, AsLogicalPlan, BallistaCodec};
+use datafusion::prelude::{ExecutionConfig, ExecutionContext};
+
+use crate::scheduler_server::event_loop::{
+    SchedulerServerEvent, SchedulerServerEventAction,
+};
+use crate::state::{ConfigBackendClient, SchedulerState};
+
+// include the generated protobuf source as a submodule
+#[allow(clippy::all)]
+pub mod externalscaler {
+    include!(concat!(env!("OUT_DIR"), "/externalscaler.rs"));
+}
+
+mod event_loop;
+mod external_scaler;
+mod grpc;
+mod task_scheduler;
+
+type ExecutorsClient = Arc<RwLock<HashMap<String, ExecutorGrpcClient<Channel>>>>;
+
+#[derive(Clone)]
+pub struct SchedulerServer<T: 'static + AsLogicalPlan, U: 'static + AsExecutionPlan> {
+    pub(crate) state: Arc<SchedulerState<T, U>>,
+    pub start_time: u128,
+    policy: TaskSchedulingPolicy,
+    executors_client: Option<ExecutorsClient>,
+    event_loop: Option<Arc<EventLoop<SchedulerServerEvent>>>,
+    ctx: Arc<RwLock<ExecutionContext>>,
+    codec: BallistaCodec<T, U>,
+}
+
+impl<T: 'static + AsLogicalPlan, U: 'static + AsExecutionPlan> SchedulerServer<T, U> {
+    pub fn new(
+        config: Arc<dyn ConfigBackendClient>,
+        namespace: String,
+        ctx: Arc<RwLock<ExecutionContext>>,
+        codec: BallistaCodec<T, U>,
+    ) -> Self {
+        SchedulerServer::new_with_policy(
+            config,
+            namespace,
+            TaskSchedulingPolicy::PullStaged,
+            ctx,
+            codec,
+        )
+    }
+
+    pub fn new_with_policy(
+        config: Arc<dyn ConfigBackendClient>,
+        namespace: String,
+        policy: TaskSchedulingPolicy,
+        ctx: Arc<RwLock<ExecutionContext>>,
+        codec: BallistaCodec<T, U>,
+    ) -> Self {
+        let state = Arc::new(SchedulerState::new(config, namespace, codec.clone()));
+
+        let (executors_client, event_loop) =
+            if matches!(policy, TaskSchedulingPolicy::PushStaged) {
+                let executors_client = Arc::new(RwLock::new(HashMap::new()));
+                let event_action: Arc<SchedulerServerEventAction<T, U>> =
+                    Arc::new(SchedulerServerEventAction::new(
+                        state.clone(),
+                        executors_client.clone(),
+                    ));
+                let event_loop =
+                    Arc::new(EventLoop::new("scheduler".to_owned(), 10000, event_action));
+                (Some(executors_client), Some(event_loop))
+            } else {
+                (None, None)
+            };
+        Self {
+            state,
+            start_time: SystemTime::now()
+                .duration_since(UNIX_EPOCH)
+                .unwrap()
+                .as_millis(),
+            policy,
+            executors_client,
+            event_loop,
+            ctx,
+            codec,
+        }
+    }
+
+    pub async fn init(&mut self) -> Result<()> {
+        {
+            // initialize state
+            let ctx = self.ctx.read().await;
+            self.state.init(&ctx).await?;
+        }
+
+        {
+            if let Some(event_loop) = self.event_loop.as_mut() {
+                // It's OK here, since we are sure the mutable reference only be used in the initialization
+                unsafe {

Review comment:
       Can we avoid this by just not wrapping the `EventLoop` in an `Arc`?




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