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Add ShutdownGuard to replace oneshot for shutdown (TraceMachina#1491)
This makes makes it easier to manage more complex shutdown cases. For example, some services might need to shutdown last, so we introduce a priority system that services can opt into.
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,128 @@ | ||
| // Copyright 2024 The NativeLink Authors. All rights reserved. | ||
| // | ||
| // 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. | ||
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| use std::collections::HashMap; | ||
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| use tokio::sync::watch; | ||
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| #[derive(Clone, Copy, Eq, PartialEq, Hash)] | ||
| pub enum Priority { | ||
| // The least important priority. | ||
| LeastImportant = 2, | ||
| // All priorities greater than 1 must be complted. | ||
| P1 = 1, | ||
| // All other priorities must be completed. | ||
| P0 = 0, | ||
| } | ||
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| impl From<usize> for Priority { | ||
| fn from(value: usize) -> Self { | ||
| match value { | ||
| 0 => Priority::P0, | ||
| 1 => Priority::P1, | ||
| _ => Priority::LeastImportant, | ||
| } | ||
| } | ||
| } | ||
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| impl From<Priority> for usize { | ||
| fn from(priority: Priority) -> usize { | ||
| match priority { | ||
| Priority::P0 => 0, | ||
| Priority::P1 => 1, | ||
| Priority::LeastImportant => 2, | ||
| } | ||
| } | ||
| } | ||
|
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| /// Tracks other services that have registered to be notified when | ||
| /// the process is being shut down. | ||
| pub struct ShutdownGuard { | ||
| priority: Priority, | ||
| tx: watch::Sender<HashMap<Priority, usize>>, | ||
| rx: watch::Receiver<HashMap<Priority, usize>>, | ||
| } | ||
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| impl ShutdownGuard { | ||
| /// Waits for all priorities less important than the given | ||
| /// priority to be completed. | ||
| pub async fn wait_for(&mut self, priority: Priority) { | ||
| if priority != self.priority { | ||
| // Promote our priority to the new priority. | ||
| self.tx.send_modify(|map| { | ||
| let old_count = map.remove(&self.priority).unwrap_or(0).saturating_sub(1); | ||
| map.insert(self.priority, old_count); | ||
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| self.priority = priority; | ||
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| let new_count = map.get(&priority).unwrap_or(&0).saturating_add(1); | ||
| map.insert(priority, new_count); | ||
| }); | ||
| } | ||
| // Ignore error because the receiver will never be closed | ||
| // if the sender is still alive here. | ||
| let _ = self | ||
| .rx | ||
| .wait_for(|map| { | ||
| let start = usize::from(priority) + 1; | ||
| let end = usize::from(Priority::LeastImportant); | ||
| for p in start..=end { | ||
| if *map.get(&p.into()).unwrap_or(&0) > 0 { | ||
| return false; | ||
| } | ||
| } | ||
| true | ||
| }) | ||
| .await; | ||
| } | ||
| } | ||
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| impl Default for ShutdownGuard { | ||
| fn default() -> Self { | ||
| let priority = Priority::LeastImportant; | ||
| let mut map = HashMap::new(); | ||
| map.insert(priority, 0); | ||
| let (tx, rx) = watch::channel(map); | ||
| Self { priority, tx, rx } | ||
| } | ||
| } | ||
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| impl Clone for ShutdownGuard { | ||
| fn clone(&self) -> Self { | ||
| self.tx.send_modify(|map| { | ||
| map.insert( | ||
| self.priority, | ||
| map.get(&Priority::LeastImportant) | ||
| .unwrap_or(&0) | ||
| .saturating_add(1), | ||
| ); | ||
| }); | ||
| Self { | ||
| priority: Priority::LeastImportant, | ||
| tx: self.tx.clone(), | ||
| rx: self.rx.clone(), | ||
| } | ||
| } | ||
| } | ||
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| impl Drop for ShutdownGuard { | ||
| fn drop(&mut self) { | ||
| self.tx.send_modify(|map| { | ||
| map.insert( | ||
| self.priority, | ||
| map.get(&self.priority).unwrap_or(&0).saturating_sub(1), | ||
| ); | ||
| }); | ||
| } | ||
| } |
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