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70 lines
2.2 KiB
70 lines
2.2 KiB
4 months ago
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# async-task
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[](
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https://github.com/smol-rs/async-task/actions)
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[](
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https://github.com/smol-rs/async-task)
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[](
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https://crates.io/crates/async-task)
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[](
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https://docs.rs/async-task)
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Task abstraction for building executors.
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To spawn a future onto an executor, we first need to allocate it on the heap and keep some
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state attached to it. The state indicates whether the future is ready for polling, waiting to
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be woken up, or completed. Such a stateful future is called a *task*.
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All executors have a queue that holds scheduled tasks:
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```rust
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let (sender, receiver) = flume::unbounded();
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```
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A task is created using either `spawn()`, `spawn_local()`, or `spawn_unchecked()` which
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return a `Runnable` and a `Task`:
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```rust
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// A future that will be spawned.
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let future = async { 1 + 2 };
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// A function that schedules the task when it gets woken up.
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let schedule = move |runnable| sender.send(runnable).unwrap();
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// Construct a task.
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let (runnable, task) = async_task::spawn(future, schedule);
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// Push the task into the queue by invoking its schedule function.
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runnable.schedule();
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```
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The `Runnable` is used to poll the task's future, and the `Task` is used to await its
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output.
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Finally, we need a loop that takes scheduled tasks from the queue and runs them:
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```rust
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for runnable in receiver {
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runnable.run();
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}
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```
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Method `run()` polls the task's future once. Then, the `Runnable`
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vanishes and only reappears when its `Waker` wakes the task, thus
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scheduling it to be run again.
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## License
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Licensed under either of
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* Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
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* MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
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at your option.
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#### Contribution
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
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dual licensed as above, without any additional terms or conditions.
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