Periodic task

Use TaskSpec::periodic for short work that should repeat after each success.

attempt
├── success ────────────► wait `every` ─────► next attempt
├── retryable failure ──► failure backoff ──► retry
└── fatal or canceled ──► stop

Every invocation is a separate attempt with its own lifecycle events. The success interval begins after the task finishes. Work duration is added to the time between starts.

This is fixed-delay scheduling, not a wall-clock or cron schedule.

This heartbeat always succeeds and repeats until Ctrl+C. run_with_os_signals installs process-wide signal handlers. Use run_until when the application owns them.

Run with cargo run --example periodic, then press Ctrl+C.

Complete program

use std::time::Duration;

use taskvisor::prelude::*;

#[tokio::main(flavor = "current_thread")]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let heartbeat: TaskRef = TaskFn::arc(|_ctx| async move {
        let now = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap_or_default();
        println!("[heartbeat] ping at {:.0}s", now.as_secs_f64());
        Ok(())
    });

    let spec = TaskSpec::periodic("heartbeat", heartbeat, Duration::from_secs(2));

    let supervisor = Supervisor::new(SupervisorConfig::default(), vec![]);
    supervisor.run_with_os_signals(vec![spec]).await?;

    Ok(())
}