TurnKeeper

TurnKeeper is a flexible, asynchronous recurring job scheduler for Rust built on the Tokio runtime. It allows scheduling tasks based on various time specifications, handles retries with exponential backoff or fixed delays, supports job cancellation and updates, and provides observability through metrics and state querying.

It uses a central coordinator task and a configurable pool of worker tasks, communicating via efficient asynchronous channels.

Features

• Flexible Scheduling: Schedule jobs using:
  • Multiple (Weekday, NaiveTime) pairs (interpreted as UTC) via from_week_day.
  • Standard CRON expressions (interpreted as UTC) via from_cron (requires the cron_schedule feature).
  • Fixed intervals (e.g., every 5 minutes) via from_interval.
  • One-time execution at a specific DateTime<Utc> via from_once.
  • No automatic scheduling via never (requires explicit trigger or initial run time).
• Configurable Retries: Set maximum retry attempts for failed jobs with exponential backoff (default) or fixed delays via with_fixed_retry_delay.
• Concurrent Execution: Run multiple jobs concurrently using a configurable worker pool (max_workers).
• Flexible Scheduling Backend: Choose between:
  • BinaryHeap (Standard Library): Minimal dependencies, cancellation checks occur lazily when a job is next to run. No efficient job updates supported.
  • HandleBased (priority-queue crate): Supports proactive cancellation removal (O log n). Required for job updates (update_job). Adds dependency (requires priority_queue_handle_based feature, enabled by default).
• Asynchronous API: Designed for integration into tokio-based applications. Provides async, blocking (add_job), and non-blocking (try_add_job) submission methods.
• Non-Blocking Submission: try_add_job provides backpressure signaling if the internal buffer is full, returning Err(SubmitError::StagingFull).
• Job Management:
  • Request cancellation of job lineages (cancel_job). Operation is idempotent.
  • Update existing job schedules or retry configurations (update_job, requires HandleBased PQ).
  • Manually trigger a job to run immediately (trigger_job_now).
• Observability:
  • Query job details (get_job_details) and list summaries (list_all_jobs). See JobDetails which includes the Schedule type.
  • Retrieve internal metrics snapshots (get_metrics_snapshot). See MetricsSnapshot for available counters/gauges.
  • Integrates with the tracing ecosystem for detailed logging.
• Helper Macro: job_fn! macro simplifies creating job execution functions.
• Job Context: (Optional job_context feature) Access job lineage ID and instance ID within the execution function via task-locals.
• Graceful & Forced Shutdown: Control scheduler termination with optional timeouts.

Installation

Add TurnKeeper and its core dependencies to your Cargo.toml. Select features as needed.

[dependencies]
turnkeeper = { version = "1.1.0", features = ["full"] } # Use "full" or select features individually
tokio = { version = "1", features = ["rt-multi-thread", "macros", "time"] } # Or features needed by your app
chrono = { version = "0.4", features = ["serde"] } # If using serde feature
uuid = { version = "1", features = ["v4", "serde"] } # If using serde feature

# Optional, but recommended for logging/debugging
tracing = "0.1"
tracing-subscriber = { version = "0.3", features = ["env-filter"] }

# Optional dependencies controlled by features:
# cron = { version = "0.12", optional = true } # Needed by "cron_schedule" feature
# priority-queue = { version = "2", optional = true } # Needed by "priority_queue_handle_based" feature (default)
# serde = { version = "1.0", features = ["derive"], optional = true } # Needed by "serde" feature

TurnKeeper's features:

• full: Enables default, cron_schedule, and serde.
• default: Enables job_context and priority_queue_handle_based.
• job_context: Enables task-local job context access.
• priority_queue_handle_based: Enables the HandleBased priority queue (required for update_job).
• cron_schedule: Enables TKJobRequest::from_cron (requires cron dependency).
• serde: Enables Serde support for query result types (JobDetails, JobSummary, MetricsSnapshot) and some internal types (requires serde dependency).

Quick Start Example

use turnkeeper::{
    TurnKeeper,
    job::TKJobRequest,
    job_fn, // Import the helper macro
    scheduler::PriorityQueueType
};
use chrono::{Duration as ChronoDuration, NaiveTime, Utc, Weekday};
use std::time::Duration as StdDuration;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;
use tracing::{error, info}; // Use tracing macros

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Basic tracing setup (optional)
    tracing_subscriber::fmt().with_max_level(tracing::Level::INFO).init();

    // 1. Build the scheduler
    info!("Building scheduler...");
    let scheduler = TurnKeeper::builder()
        .max_workers(2) // Run up to 2 jobs at once
        // PriorityQueueType::HandleBased is the default
        .build()?;
    info!("Scheduler built.");

    // 2. Define job execution logic using job_fn! macro
    let counter = Arc::new(AtomicUsize::new(0));
    let job_fn = job_fn! { // Macro handles boxing/pinning
        {
            // Optional setup block (runs immediately when closure is created)
            let job_counter = counter.clone(); // Clone Arcs needed by the async block
        }
        { // Main async logic block (captures variables from setup block)
            let count = job_counter.fetch_add(1, Ordering::Relaxed) + 1;
            info!("Simple job executed! Count: {}", count);
            tokio::time::sleep(StdDuration::from_millis(50)).await; // Simulate work
            true // Return bool for success/failure
        }
    };

    // 3. Define job requests using different schedules
    let job_req_once = TKJobRequest::from_once(
        "Run Once Job",
        Utc::now() + ChronoDuration::seconds(2),
        1 // Allow 1 retry on failure
    );

    let mut job_req_interval = TKJobRequest::from_interval(
        "Interval Job",
        StdDuration::from_secs(5), // Run every 5 seconds
        0
    );
    // Interval job's first run occurs ~5s after coordinator processes it,
    // unless overridden:
    job_req_interval.with_initial_run_time(Utc::now() + ChronoDuration::seconds(1));


    // 4. Submit the jobs (using async variant)
    info!("Submitting jobs...");
    match scheduler.add_job_async(job_req_once, job_fn.clone()).await { // Clone job_fn if reused
        Ok(job_id) => info!("Once job submitted with ID: {}", job_id),
        Err(e) => error!("Failed to submit Once job: {:?}", e),
    }
    match scheduler.add_job_async(job_req_interval, job_fn).await {
        Ok(job_id) => info!("Interval job submitted with ID: {}", job_id),
        Err(e) => error!("Failed to submit Interval job: {:?}", e),
    }


    // 5. Let the scheduler run for a while
    info!("Waiting for jobs to run (approx 10 seconds)...");
    tokio::time::sleep(StdDuration::from_secs(10)).await;

    // 6. Query metrics (optional)
    match scheduler.get_metrics_snapshot().await {
        Ok(metrics) => info!("Current Metrics: {:#?}", metrics),
        Err(e) => error!("Failed to get metrics: {}", e),
    }

    // 7. Shut down gracefully
    info!("Requesting graceful shutdown...");
    match scheduler.shutdown_graceful(Some(StdDuration::from_secs(10))).await {
        Ok(()) => info!("Scheduler shut down successfully."),
        Err(e) => error!("Shutdown failed: {}", e),
    }

    Ok(())
}

Configuration (SchedulerBuilder)

Use TurnKeeper::builder() to configure the scheduler before starting it via .build():

• .max_workers(usize): Required. Sets the maximum number of concurrently running jobs (must be > 0).
• .priority_queue(PriorityQueueType): Optional. Choose between BinaryHeap and HandleBased (default, requires priority_queue_handle_based feature). See PriorityQueueType docs for functional differences.
• .staging_buffer_size(usize): Optional. Size of the incoming job submission buffer. Default: 128.
• .command_buffer_size(usize): Optional. Size of the internal command buffer (queries, etc.). Default: 128.
• .job_dispatch_buffer_size(usize): Optional. Size of the coordinator-to-worker dispatch channel. Must be >= 1. Default: 1 (provides backpressure).

Defining Jobs (TKJobRequest)

Create a TKJobRequest using specific constructors:

• from_week_day(...): Takes name, Vec<(Weekday, NaiveTime)> (schedule), max_retries. Schedule times are interpreted as UTC.
• from_cron(...): Takes name, &str (cron expression), max_retries. Requires the cron_schedule feature. Expression interpreted as UTC.
• from_interval(...): Takes name, std::time::Duration (interval), max_retries. Interval starts after the previous scheduled/run time.
• from_once(...): Takes name, DateTime<Utc> (run time), max_retries.
• never(...): Takes name, max_retries. Job has no automatic schedule.
• with_fixed_retry_delay(...): Alternative constructor that takes a Schedule and a StdDuration for fixed retry delays.

Use .with_initial_run_time(DateTime<Utc>) to set a specific first execution time. This overrides the schedule calculation for the first run and is required for Schedule::Never jobs to run without a manual trigger.

The schedule type itself is defined by the Schedule enum.

Job Function (BoxedExecFn)

The function executed by the worker must match the BoxedExecFn type alias:

use std::pin::Pin;
use std::future::Future;

type BoxedExecFn = Box<
    dyn Fn() -> Pin<Box<dyn Future<Output = bool> + Send + 'static>>
    + Send + Sync + 'static,
>;

• It must be an async function or closure returning a Pin<Box<dyn Future>>. The job_fn! macro simplifies this.
• The Future must resolve to bool (true = success, false = logical failure).
• The function/closure and the Future must be Send + Sync + 'static. Use Arc for shared state captured by closures.
• Panics within the function are caught and treated as failures by the scheduler, triggering retries if configured.

API Highlights

See the API Reference Documentation on docs.rs for full details.

• add_job_async / try_add_job / add_job: Submit jobs using TKJobRequest, returns Result<TKJobId, SubmitError>. IDs (TKJobId) are generated before sending to the coordinator.
• cancel_job: Request lineage cancellation by TKJobId.
• update_job: Update schedule/retries for existing job (HandleBased PQ required).
• trigger_job_now: Manually run a job instance now.
• get_job_details / list_all_jobs: Query job status by TKJobId or list all. Returns details including the Schedule.
• get_metrics_snapshot: Get performance counters and gauges. Includes distinct counts for lineage cancellation vs. discarded instances.
• shutdown_graceful / shutdown_force: Control termination with optional timeout.

Cancellation & Updates

• cancel_job marks a job lineage (TKJobId) for cancellation.
• If using PriorityQueueType::HandleBased (default), the scheduler attempts to proactively remove the currently scheduled instance from the queue (O log n).
• If using PriorityQueueType::BinaryHeap, the scheduled instance is only discarded when it reaches the front of the queue and is checked before dispatch.
• update_job allows changing the Schedule and max_retries of a non-cancelled job. Requires the HandleBased PQ type. If the schedule changes, the next instance is rescheduled accordingly.

License

This project is licensed under the Mozilla Public License Version 2.0 (LICENSE or https://opensource.org/licenses/MPL-2.0).