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224//! Command lane system — lane-based command queue with concurrency control.
//!
//! Routes different types of work through separate lanes with independent
//! concurrency limits to prevent starvation:
//! - Main: user messages (serialized, 1 at a time)
//! - Cron: scheduled jobs (2 concurrent)
//! - Subagent: spawned child agents (3 concurrent)
use std::sync::Arc;
use tokio::sync::Semaphore;
/// Command lane type.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Lane {
/// User-facing message processing (1 concurrent).
Main,
/// Cron/scheduled job execution (2 concurrent).
Cron,
/// Subagent spawn/call execution (3 concurrent).
Subagent,
}
impl std::fmt::Display for Lane {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Lane::Main => write!(f, "main"),
Lane::Cron => write!(f, "cron"),
Lane::Subagent => write!(f, "subagent"),
}
}
}
/// Lane occupancy snapshot.
#[derive(Debug, Clone)]
pub struct LaneOccupancy {
/// Lane type.
pub lane: Lane,
/// Current number of active tasks.
pub active: u32,
/// Maximum concurrent tasks.
pub capacity: u32,
}
/// Command queue with lane-based concurrency control.
#[derive(Debug, Clone)]
pub struct CommandQueue {
main_sem: Arc<Semaphore>,
cron_sem: Arc<Semaphore>,
subagent_sem: Arc<Semaphore>,
main_capacity: u32,
cron_capacity: u32,
subagent_capacity: u32,
}
impl CommandQueue {
/// Create a new command queue with default capacities.
pub fn new() -> Self {
Self {
main_sem: Arc::new(Semaphore::new(1)),
cron_sem: Arc::new(Semaphore::new(2)),
subagent_sem: Arc::new(Semaphore::new(3)),
main_capacity: 1,
cron_capacity: 2,
subagent_capacity: 3,
}
}
/// Create with custom capacities.
pub fn with_capacities(main: u32, cron: u32, subagent: u32) -> Self {
Self {
main_sem: Arc::new(Semaphore::new(main as usize)),
cron_sem: Arc::new(Semaphore::new(cron as usize)),
subagent_sem: Arc::new(Semaphore::new(subagent as usize)),
main_capacity: main,
cron_capacity: cron,
subagent_capacity: subagent,
}
}
/// Submit work to a lane. Acquires a permit, executes the future, releases.
///
/// Returns `Err` if the semaphore is closed (shutdown).
pub async fn submit<F, T>(&self, lane: Lane, work: F) -> Result<T, String>
where
F: std::future::Future<Output = T>,
{
let sem = self.semaphore_for(lane);
let _permit = sem
.acquire()
.await
.map_err(|_| format!("Lane {} is closed", lane))?;
Ok(work.await)
}
/// Try to submit work without waiting (non-blocking).
///
/// Returns `None` if the lane is at capacity.
pub async fn try_submit<F, T>(&self, lane: Lane, work: F) -> Option<T>
where
F: std::future::Future<Output = T>,
{
let sem = self.semaphore_for(lane);
let _permit = sem.try_acquire().ok()?;
Some(work.await)
}
/// Get current occupancy for all lanes.
pub fn occupancy(&self) -> Vec<LaneOccupancy> {
vec![
LaneOccupancy {
lane: Lane::Main,
active: self.main_capacity - self.main_sem.available_permits() as u32,
capacity: self.main_capacity,
},
LaneOccupancy {
lane: Lane::Cron,
active: self.cron_capacity - self.cron_sem.available_permits() as u32,
capacity: self.cron_capacity,
},
LaneOccupancy {
lane: Lane::Subagent,
active: self.subagent_capacity - self.subagent_sem.available_permits() as u32,
capacity: self.subagent_capacity,
},
]
}
fn semaphore_for(&self, lane: Lane) -> &Arc<Semaphore> {
match lane {
Lane::Main => &self.main_sem,
Lane::Cron => &self.cron_sem,
Lane::Subagent => &self.subagent_sem,
}
}
}
impl Default for CommandQueue {
fn default() -> Self {
Self::new()
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::sync::atomic::{AtomicU32, Ordering};
#[tokio::test]
async fn test_main_lane_serialization() {
let queue = CommandQueue::new();
let counter = Arc::new(AtomicU32::new(0));
// Main lane has capacity 1 — tasks should serialize
let c1 = counter.clone();
let result = queue
.submit(Lane::Main, async move {
c1.fetch_add(1, Ordering::SeqCst);
42
})
.await;
assert_eq!(result.unwrap(), 42);
assert_eq!(counter.load(Ordering::SeqCst), 1);
}
#[tokio::test]
async fn test_cron_lane_parallel() {
let queue = Arc::new(CommandQueue::new());
let counter = Arc::new(AtomicU32::new(0));
let mut handles = Vec::new();
for _ in 0..2 {
let q = queue.clone();
let c = counter.clone();
handles.push(tokio::spawn(async move {
q.submit(Lane::Cron, async move {
c.fetch_add(1, Ordering::SeqCst);
tokio::time::sleep(std::time::Duration::from_millis(10)).await;
})
.await
}));
}
for h in handles {
h.await.unwrap().unwrap();
}
assert_eq!(counter.load(Ordering::SeqCst), 2);
}
#[tokio::test]
async fn test_occupancy() {
let queue = CommandQueue::new();
let occ = queue.occupancy();
assert_eq!(occ.len(), 3);
assert_eq!(occ[0].active, 0);
assert_eq!(occ[0].capacity, 1);
assert_eq!(occ[1].capacity, 2);
assert_eq!(occ[2].capacity, 3);
}
#[tokio::test]
async fn test_try_submit_when_full() {
let queue = CommandQueue::with_capacities(1, 1, 1);
// Acquire the main permit
let sem = queue.main_sem.clone();
let _permit = sem.acquire().await.unwrap();
// try_submit should return None since lane is full
let result = queue.try_submit(Lane::Main, async { 42 }).await;
assert!(result.is_none());
}
#[tokio::test]
async fn test_custom_capacities() {
let queue = CommandQueue::with_capacities(2, 4, 6);
let occ = queue.occupancy();
assert_eq!(occ[0].capacity, 2);
assert_eq!(occ[1].capacity, 4);
assert_eq!(occ[2].capacity, 6);
}
}