295 lines
9.0 KiB
Rust
295 lines
9.0 KiB
Rust
//! # Managing Timeouts in Tasks
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//!
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//! This example demonstrates how to implement timeout patterns in DAG tasks using
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//! tokio's timeout utilities for time-bounded execution.
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//!
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//! ## What You'll Learn
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//! - How to implement timeouts using `tokio::time::timeout`
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//! - How to build tasks with built-in timeout logic
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//! - How to handle timeout errors as Result types
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//! - How to apply timeouts at both task-level and DAG-level
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//!
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//! ## Timeout Patterns
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//!
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//! **1. Task-Level Timeout** - Individual task with timeout
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//! ```rust
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//! async fn run(&mut self) -> Result<String, String> {
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//! let work = async { /* ... */ };
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//! match timeout(Duration::from_millis(self.timeout_ms), work).await {
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//! Ok(result) => Ok(result),
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//! Err(_) => Err("Task timed out".to_string()),
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//! }
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//! }
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//! ```
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//!
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//! **2. DAG-Level Timeout** - Entire workflow with timeout
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//! ```rust
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//! match timeout(dag_timeout, dag.run(|fut| tokio::spawn(fut).map(Result::unwrap)).await {
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//! Ok(result) => { /* DAG completed */ },
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//! Err(_) => { /* DAG timed out */ },
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//! }
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//! ```
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//!
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//! ## Workflow Diagram
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//! ```text
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//! ┌─────────────┐
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//! │ FastTask │ (completes in 100ms)
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//! │ (timeout │ ───► Ok("Fast task completed")
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//! │ 500ms) │
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//! └─────────────┘
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//!
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//! ┌─────────────┐
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//! │ SlowTask │ (takes 1000ms)
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//! │ (timeout │ ───► Err("Task timed out after 200ms")
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//! │ 200ms) │
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//! └─────────────┘
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//! │
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//! └──────►┌──────────────┐
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//! │ProcessResult │ ───► "✗ Task timed out..."
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//! └──────────────┘
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//! ```
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//!
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//! ## Key Concepts
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//! - **Timeout as error**: Timeouts produce `Err` results that propagate through the DAG
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//! - **Error as data**: Use Result<T, E> to represent timeout states
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//! - **Graceful degradation**: Downstream tasks can handle timeout errors
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//! - **Time-bounded execution**: Enforce SLAs and prevent runaway tasks
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//!
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//! ## Use Cases
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//! - API calls with timeout limits
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//! - SLA enforcement in workflows
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//! - Preventing resource exhaustion from slow tasks
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//! - Circuit breaker patterns
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//! - External service integration with timeouts
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//!
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//! ## Running This Example
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//! ```bash
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//! cargo run --example timeout
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//! ```
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//!
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//! ## Expected Output
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//! ```text
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//! === Timeout Example ===
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//!
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//! Example 1: All tasks complete successfully
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//! Fast task: Ok("Fast task completed")
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//! Timed task: Ok("Work completed in 100ms")
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//!
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//! Example 2: Task exceeds timeout
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//! Result: ✗ Task timed out after 200ms (work would take 1000ms)
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//!
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//! Example 3: Parallel tasks with different speeds
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//! Fast task 1: Ok("Fast task completed")
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//! Fast task 2: Ok("Fast task completed")
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//! Slow task: Ok("Slow task completed after 500ms")
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//! Timed task 1: Ok("Work completed in 100ms")
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//! Timed task 2: Err("Task timed out after 200ms...")
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//!
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//! Example 4: Downstream tasks handling timeout errors
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//! Processed 1: ✗ Task timed out after 100ms (work would take 500ms)
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//! Processed 2: ✗ Task timed out after 100ms (work would take 500ms)
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//!
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//! Example 5: Whole-DAG timeout
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//! DAG completed within timeout
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//! Task 1: Ok("Slow task completed after 200ms")
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//! Task 2: Ok("Slow task completed after 200ms")
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//! Task 3: Ok("Slow task completed after 200ms")
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//!
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//! === Timeout Example Complete ===
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//! ```
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use dagx::{task, DagRunner};
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use futures::FutureExt;
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use tokio::time::{sleep, timeout, Duration};
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// Fast task that completes quickly
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struct FastTask;
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#[task]
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impl FastTask {
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async fn run() -> Result<String, String> {
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sleep(Duration::from_millis(100)).await;
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Ok("Fast task completed".to_string())
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}
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}
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// Slow task that takes a long time
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struct SlowTask {
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duration_ms: u64,
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}
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#[task]
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impl SlowTask {
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async fn run(&mut self) -> Result<String, String> {
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sleep(Duration::from_millis(self.duration_ms)).await;
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Ok(format!("Slow task completed after {}ms", self.duration_ms))
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}
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}
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// Task with built-in timeout
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struct TaskWithTimeout {
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work_duration_ms: u64,
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timeout_ms: u64,
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}
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#[task]
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impl TaskWithTimeout {
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async fn run(&mut self) -> Result<String, String> {
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let work = async {
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sleep(Duration::from_millis(self.work_duration_ms)).await;
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format!("Work completed in {}ms", self.work_duration_ms)
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};
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match timeout(Duration::from_millis(self.timeout_ms), work).await {
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Ok(result) => Ok(result),
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Err(_) => Err(format!(
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"Task timed out after {}ms (work would take {}ms)",
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self.timeout_ms, self.work_duration_ms
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)),
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}
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}
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}
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// Task that processes results (including timeouts)
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struct ProcessResult;
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#[task]
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impl ProcessResult {
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async fn run(input: &Result<String, String>) -> String {
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match input {
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Ok(msg) => format!("✓ {}", msg),
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Err(err) => format!("✗ {}", err),
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}
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}
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}
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#[tokio::main]
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async fn main() {
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println!("=== Timeout Example ===\n");
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// Example 1: All tasks complete within timeout
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println!("Example 1: All tasks complete successfully");
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{
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let dag = DagRunner::new();
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let fast = dag.add_task(FastTask);
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let timed = dag.add_task(TaskWithTimeout {
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work_duration_ms: 100,
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timeout_ms: 500,
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});
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dag.run(|fut| tokio::spawn(fut).map(Result::unwrap))
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.await
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.unwrap();
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println!("Fast task: {:?}", dag.get(fast).unwrap());
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println!("Timed task: {:?}\n", dag.get(timed).unwrap());
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}
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// Example 2: Task exceeds timeout
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println!("Example 2: Task exceeds timeout");
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{
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let dag = DagRunner::new();
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let timed = dag.add_task(TaskWithTimeout {
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work_duration_ms: 1000,
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timeout_ms: 200,
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});
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let processed = dag.add_task(ProcessResult).depends_on(&timed);
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dag.run(|fut| tokio::spawn(fut).map(Result::unwrap))
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.await
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.unwrap();
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println!("Result: {}\n", dag.get(processed).unwrap());
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}
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// Example 3: Mixed fast and slow tasks
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println!("Example 3: Parallel tasks with different speeds");
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{
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let dag = DagRunner::new();
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let fast1 = dag.add_task(FastTask);
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let fast2 = dag.add_task(FastTask);
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let slow = dag.add_task(SlowTask { duration_ms: 500 });
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let timed1 = dag.add_task(TaskWithTimeout {
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work_duration_ms: 100,
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timeout_ms: 200,
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});
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let timed2 = dag.add_task(TaskWithTimeout {
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work_duration_ms: 300,
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timeout_ms: 200,
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});
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dag.run(|fut| tokio::spawn(fut).map(Result::unwrap))
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.await
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.unwrap();
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println!("Fast task 1: {:?}", dag.get(fast1).unwrap());
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println!("Fast task 2: {:?}", dag.get(fast2).unwrap());
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println!("Slow task: {:?}", dag.get(slow).unwrap());
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println!("Timed task 1: {:?}", dag.get(timed1).unwrap());
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println!("Timed task 2: {:?}\n", dag.get(timed2).unwrap());
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}
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// Example 4: Cascading timeout errors
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println!("Example 4: Downstream tasks handling timeout errors");
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{
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let dag = DagRunner::new();
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let source = dag.add_task(TaskWithTimeout {
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work_duration_ms: 500,
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timeout_ms: 100,
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});
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let processed1 = dag.add_task(ProcessResult).depends_on(&source);
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let processed2 = dag.add_task(ProcessResult).depends_on(&source);
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dag.run(|fut| tokio::spawn(fut).map(Result::unwrap))
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.await
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.unwrap();
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println!("Processed 1: {}", dag.get(processed1).unwrap());
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println!("Processed 2: {}\n", dag.get(processed2).unwrap());
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}
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// Example 5: Implementing whole-DAG timeout
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println!("Example 5: Whole-DAG timeout");
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{
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let dag = DagRunner::new();
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let t1 = dag.add_task(SlowTask { duration_ms: 200 });
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let t2 = dag.add_task(SlowTask { duration_ms: 200 });
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let t3 = dag.add_task(SlowTask { duration_ms: 200 });
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// Run the entire DAG with a timeout
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let dag_timeout = Duration::from_millis(500);
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match timeout(
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dag_timeout,
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dag.run(|fut| tokio::spawn(fut).map(Result::unwrap)),
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)
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.await
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{
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Ok(result) => {
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result.unwrap();
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println!("DAG completed within timeout");
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println!("Task 1: {:?}", dag.get(t1).unwrap());
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println!("Task 2: {:?}", dag.get(t2).unwrap());
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println!("Task 3: {:?}", dag.get(t3).unwrap());
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}
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Err(_) => {
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eprintln!(
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"DAG execution timed out after {}ms",
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dag_timeout.as_millis()
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);
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}
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}
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}
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println!("\n=== Timeout Example Complete ===");
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}
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