-
Notifications
You must be signed in to change notification settings - Fork 234
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Merge pull request #2040 from bendk/blocking-task-queue-without-speci…
…alized-code Blocking task queue without specialized code
- Loading branch information
Showing
9 changed files
with
333 additions
and
132 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,28 @@ | ||
| This crate is a toy build an async API client, with some parts implemented in Rust and some parts | ||
| implemented in the foreign language. Each side makes async calls across the FFI. | ||
|
|
||
| The motivation is to show how to build an async-based Rust library, using a foreign async executor to drive the futures. | ||
| Note that the Rust code does not start any threads of its own, nor does it use startup an async runtime like tokio. | ||
| Instead, it awaits async calls to the foreign code and the foreign executor manages the threads. | ||
|
|
||
| There are two basic ways the Rust code in this crate awaits the foreign code: | ||
|
|
||
| ## API calls | ||
|
|
||
| API calls are the simple case. | ||
| Rust awaits an HTTP call to the foreign side, then uses `serde` to parse the JSON into a structured response. | ||
| As long as the Rust code is "non-blocking" this system should work fine. | ||
| Note: there is not a strict definition for "non-blocking", but typically it means not performing IO and not executing a long-running CPU operation. | ||
|
|
||
| ## Blocking tasks | ||
|
|
||
| The more difficult case is a blocking Rust call. | ||
| The example from this crate is reading the API credentials from disk. | ||
| The `tasks.rs` module and the foreign implementations of the `TaskRunner` interface are an experiment to show how this can be accomplished using async callback methods. | ||
|
|
||
| The code works, but is a bit clunky. | ||
| For example requiring that the task closure is `'static` creates some extra work for the `load_credentials` function. | ||
| It also requires an extra `Mutex` and `Arc`. | ||
|
|
||
| The UniFFI team is looking for ways to simplify this process by handling it natively in UniFFI, see https://github.com/mozilla/uniffi-rs/pull/1837. | ||
| If you are writing Rust code that needs to make async blocking calls, please tell us about your use case which will help us develop the feature. |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,76 @@ | ||
| /* This Source Code Form is subject to the terms of the Mozilla Public | ||
| * License, v. 2.0. If a copy of the MPL was not distributed with this | ||
| * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ | ||
|
|
||
| use crate::{run_task, ApiError, Result, TaskRunner}; | ||
| use std::sync::Arc; | ||
|
|
||
| #[async_trait::async_trait] | ||
| pub trait HttpClient: Send + Sync { | ||
| async fn fetch(&self, url: String, credentials: String) -> Result<String>; | ||
| } | ||
|
|
||
| impl From<serde_json::Error> for ApiError { | ||
| fn from(e: serde_json::Error) -> Self { | ||
| Self::Json { | ||
| reason: e.to_string(), | ||
| } | ||
| } | ||
| } | ||
|
|
||
| #[derive(Debug, serde::Deserialize)] | ||
| pub struct Issue { | ||
| pub url: String, | ||
| pub title: String, | ||
| pub state: IssueState, | ||
| } | ||
|
|
||
| #[derive(Debug, serde::Deserialize)] | ||
| pub enum IssueState { | ||
| #[serde(rename = "open")] | ||
| Open, | ||
| #[serde(rename = "closed")] | ||
| Closed, | ||
| } | ||
|
|
||
| pub struct ApiClient { | ||
| http_client: Arc<dyn HttpClient>, | ||
| task_runner: Arc<dyn TaskRunner>, | ||
| } | ||
|
|
||
| impl ApiClient { | ||
| // Pretend this is a blocking call that needs to load the credentials from disk/network | ||
| fn load_credentials_sync(&self) -> String { | ||
| String::from("username:password") | ||
| } | ||
|
|
||
| async fn load_credentials(self: Arc<Self>) -> String { | ||
| let self_cloned = Arc::clone(&self); | ||
| run_task(&self.task_runner, move || { | ||
| self_cloned.load_credentials_sync() | ||
| }) | ||
| .await | ||
| } | ||
| } | ||
|
|
||
| impl ApiClient { | ||
| pub fn new(http_client: Arc<dyn HttpClient>, task_runner: Arc<dyn TaskRunner>) -> Self { | ||
| Self { | ||
| http_client, | ||
| task_runner, | ||
| } | ||
| } | ||
|
|
||
| pub async fn get_issue( | ||
| self: Arc<Self>, | ||
| owner: String, | ||
| repository: String, | ||
| issue_number: u32, | ||
| ) -> Result<Issue> { | ||
| let credentials = self.clone().load_credentials().await; | ||
| let url = | ||
| format!("https://api.github.com/repos/{owner}/{repository}/issues/{issue_number}"); | ||
| let body = self.http_client.fetch(url, credentials).await?; | ||
| Ok(serde_json::from_str(&body)?) | ||
| } | ||
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,90 @@ | ||
| /* This Source Code Form is subject to the terms of the Mozilla Public | ||
| * License, v. 2.0. If a copy of the MPL was not distributed with this | ||
| * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ | ||
|
|
||
| use std::sync::{Arc, Mutex}; | ||
|
|
||
| #[async_trait::async_trait] | ||
| pub trait TaskRunner: Send + Sync { | ||
| async fn run_task(&self, task: Arc<dyn RustTask>); | ||
| } | ||
|
|
||
| pub trait RustTask: Send + Sync { | ||
| fn execute(&self); | ||
| } | ||
|
|
||
| pub async fn run_task<F, T>(runner: &Arc<dyn TaskRunner>, closure: F) -> T | ||
| where | ||
| F: FnOnce() -> T + Send + Sync + 'static, | ||
| T: Send + 'static, | ||
| { | ||
| let closure = Arc::new(TaskClosure::new(closure)); | ||
| runner | ||
| .run_task(Arc::clone(&closure) as Arc<dyn RustTask>) | ||
| .await; | ||
| closure.take_result() | ||
| } | ||
|
|
||
| struct TaskClosure<F, T> | ||
| where | ||
| F: FnOnce() -> T + Send + Sync, | ||
| T: Send, | ||
| { | ||
| inner: Mutex<TaskClosureInner<F, T>>, | ||
| } | ||
|
|
||
| enum TaskClosureInner<F, T> | ||
| where | ||
| F: FnOnce() -> T + Send + Sync, | ||
| T: Send, | ||
| { | ||
| Pending(F), | ||
| Running, | ||
| Complete(T), | ||
| Finished, | ||
| } | ||
|
|
||
| impl<F, T> TaskClosure<F, T> | ||
| where | ||
| F: FnOnce() -> T + Send + Sync, | ||
| T: Send, | ||
| { | ||
| fn new(closure: F) -> Self { | ||
| Self { | ||
| inner: Mutex::new(TaskClosureInner::Pending(closure)), | ||
| } | ||
| } | ||
|
|
||
| fn take_result(&self) -> T { | ||
| let mut inner = self.inner.lock().unwrap(); | ||
| match *inner { | ||
| TaskClosureInner::Pending(_) => panic!("Task never ran"), | ||
| TaskClosureInner::Running => panic!("Task still running"), | ||
| TaskClosureInner::Finished => panic!("Task already finished"), | ||
| TaskClosureInner::Complete(_) => (), | ||
| }; | ||
| match std::mem::replace(&mut *inner, TaskClosureInner::Finished) { | ||
| TaskClosureInner::Complete(v) => v, | ||
| _ => unreachable!(), | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl<F, T> RustTask for TaskClosure<F, T> | ||
| where | ||
| F: FnOnce() -> T + Send + Sync, | ||
| T: Send, | ||
| { | ||
| fn execute(&self) { | ||
| let mut inner = self.inner.lock().unwrap(); | ||
| match std::mem::replace(&mut *inner, TaskClosureInner::Running) { | ||
| TaskClosureInner::Pending(f) => { | ||
| let result = f(); | ||
| *inner = TaskClosureInner::Complete(result) | ||
| } | ||
| TaskClosureInner::Running => panic!("Task already started"), | ||
| TaskClosureInner::Complete(_) => panic!("Task already executed"), | ||
| TaskClosureInner::Finished => panic!("Task already finished"), | ||
| } | ||
| } | ||
| } |
Oops, something went wrong.