datafusion_common_runtime/
common.rs

1// Licensed to the Apache Software Foundation (ASF) under one
2// or more contributor license agreements.  See the NOTICE file
3// distributed with this work for additional information
4// regarding copyright ownership.  The ASF licenses this file
5// to you under the Apache License, Version 2.0 (the
6// "License"); you may not use this file except in compliance
7// with the License.  You may obtain a copy of the License at
8//
9//   http://www.apache.org/licenses/LICENSE-2.0
10//
11// Unless required by applicable law or agreed to in writing,
12// software distributed under the License is distributed on an
13// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
14// KIND, either express or implied.  See the License for the
15// specific language governing permissions and limitations
16// under the License.
17
18use std::future::Future;
19
20use tokio::task::{JoinError, JoinSet};
21
22/// Helper that  provides a simple API to spawn a single task and join it.
23/// Provides guarantees of aborting on `Drop` to keep it cancel-safe.
24///
25/// Technically, it's just a wrapper of `JoinSet` (with size=1).
26#[derive(Debug)]
27pub struct SpawnedTask<R> {
28    inner: JoinSet<R>,
29}
30
31impl<R: 'static> SpawnedTask<R> {
32    pub fn spawn<T>(task: T) -> Self
33    where
34        T: Future<Output = R>,
35        T: Send + 'static,
36        R: Send,
37    {
38        let mut inner = JoinSet::new();
39        inner.spawn(task);
40        Self { inner }
41    }
42
43    pub fn spawn_blocking<T>(task: T) -> Self
44    where
45        T: FnOnce() -> R,
46        T: Send + 'static,
47        R: Send,
48    {
49        let mut inner = JoinSet::new();
50        inner.spawn_blocking(task);
51        Self { inner }
52    }
53
54    /// Joins the task, returning the result of join (`Result<R, JoinError>`).
55    pub async fn join(mut self) -> Result<R, JoinError> {
56        self.inner
57            .join_next()
58            .await
59            .expect("`SpawnedTask` instance always contains exactly 1 task")
60    }
61
62    /// Joins the task and unwinds the panic if it happens.
63    pub async fn join_unwind(self) -> Result<R, JoinError> {
64        self.join().await.map_err(|e| {
65            // `JoinError` can be caused either by panic or cancellation. We have to handle panics:
66            if e.is_panic() {
67                std::panic::resume_unwind(e.into_panic());
68            } else {
69                // Cancellation may be caused by two reasons:
70                // 1. Abort is called, but since we consumed `self`, it's not our case (`JoinHandle` not accessible outside).
71                // 2. The runtime is shutting down.
72                log::warn!("SpawnedTask was polled during shutdown");
73                e
74            }
75        })
76    }
77}
78
79#[cfg(test)]
80mod tests {
81    use super::*;
82
83    use std::future::{pending, Pending};
84
85    use tokio::runtime::Runtime;
86
87    #[tokio::test]
88    async fn runtime_shutdown() {
89        let rt = Runtime::new().unwrap();
90        let task = rt
91            .spawn(async {
92                SpawnedTask::spawn(async {
93                    let fut: Pending<()> = pending();
94                    fut.await;
95                    unreachable!("should never return");
96                })
97            })
98            .await
99            .unwrap();
100
101        // caller shutdown their DF runtime (e.g. timeout, error in caller, etc)
102        rt.shutdown_background();
103
104        // race condition
105        // poll occurs during shutdown (buffered stream poll calls, etc)
106        assert!(matches!(
107            task.join_unwind().await,
108            Err(e) if e.is_cancelled()
109        ));
110    }
111
112    #[tokio::test]
113    #[should_panic(expected = "foo")]
114    async fn panic_resume() {
115        // this should panic w/o an `unwrap`
116        SpawnedTask::spawn(async { panic!("foo") })
117            .join_unwind()
118            .await
119            .ok();
120    }
121}
datafusion_common_runtime/common.rs

datafusion_common_runtime/
common.rs
