85 lines
2.1 KiB
Rust
85 lines
2.1 KiB
Rust
//! An executor with task priorities.
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use std::thread;
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use async_executor::{Executor, Task};
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use futures_lite::{future, prelude::*};
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/// Task priority.
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#[repr(usize)]
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#[derive(Debug, Clone, Copy)]
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enum Priority {
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High = 0,
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Medium = 1,
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Low = 2,
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}
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/// An executor with task priorities.
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///
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/// Tasks with lower priorities only get polled when there are no tasks with higher priorities.
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struct PriorityExecutor<'a> {
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ex: [Executor<'a>; 3],
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}
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impl<'a> PriorityExecutor<'a> {
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/// Creates a new executor.
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const fn new() -> PriorityExecutor<'a> {
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PriorityExecutor {
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ex: [Executor::new(), Executor::new(), Executor::new()],
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}
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}
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/// Spawns a task with the given priority.
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fn spawn<T: Send + 'a>(
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&self,
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priority: Priority,
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future: impl Future<Output = T> + Send + 'a,
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) -> Task<T> {
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self.ex[priority as usize].spawn(future)
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}
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/// Runs the executor forever.
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async fn run(&self) {
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loop {
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for _ in 0..200 {
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let t0 = self.ex[0].tick();
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let t1 = self.ex[1].tick();
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let t2 = self.ex[2].tick();
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// Wait until one of the ticks completes, trying them in order from highest
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// priority to lowest priority.
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t0.or(t1).or(t2).await;
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}
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// Yield every now and then.
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future::yield_now().await;
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}
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}
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}
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fn main() {
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static EX: PriorityExecutor<'_> = PriorityExecutor::new();
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// Spawn a thread running the executor forever.
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thread::spawn(|| future::block_on(EX.run()));
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let mut tasks = Vec::new();
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for _ in 0..20 {
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// Choose a random priority.
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let choice = [Priority::High, Priority::Medium, Priority::Low];
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let priority = choice[fastrand::usize(..choice.len())];
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// Spawn a task with this priority.
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tasks.push(EX.spawn(priority, async move {
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println!("{:?}", priority);
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future::yield_now().await;
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println!("{:?}", priority);
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}));
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}
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for task in tasks {
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future::block_on(task);
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}
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}
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