144 lines
4.0 KiB
Rust
144 lines
4.0 KiB
Rust
//! # Pattern: Fan-In (N→1 Dependencies)
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//!
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//! This example demonstrates the fan-in pattern where multiple independent source
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//! tasks produce values that are aggregated by a single downstream task.
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//!
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//! ## What You'll Learn
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//! - How to create many-to-one task dependencies
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//! - How to aggregate results from multiple upstream tasks
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//! - How parameter order in `depends_on()` maps to function parameters
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//! - How independent tasks run in parallel before aggregation
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//!
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//! ## Pattern Diagram
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//! ```text
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//! ┌──────────┐ ┌─────────┐ ┌──────────┐ ┌────────────┐
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//! │FetchName │ │FetchAge │ │FetchCity │ │CheckActive │
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//! └────┬─────┘ └────┬────┘ └────┬─────┘ └──────┬─────┘
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//! │ │ │ │
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//! "Alice" 30 "San Francisco" true
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//! │ │ │ │
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//! └─────────────┴─────────────┴───────────────┘
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//! │
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//! ┌───────▼────────┐
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//! │ BuildProfile │
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//! └────────────────┘
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//! │
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//! "User Profile..."
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//! ```
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//!
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//! ## Key Concepts
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//! - **Fan-in**: Multiple tasks' outputs are consumed by a single downstream task
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//! - **Aggregation**: Combining multiple values into a single result
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//! - **Parameter order**: The order in `.depends_on((&a, &b, &c))` must match
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//! the function signature `fn run(a: &T1, b: &T2, c: &T3)`
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//!
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//! ## Use Cases
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//! - Aggregating data from multiple API endpoints
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//! - Combining results from parallel computations
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//! - Building composite objects from multiple sources
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//! - Waiting for multiple prerequisites before proceeding
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//!
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//! ## Running This Example
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//! ```bash
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//! cargo run --example fan_in
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//! ```
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//!
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//! ## Expected Output
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//! ```text
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//! Running fan-in DAG...
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//!
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//! Fetching name...
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//! Fetching age...
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//! Fetching city...
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//! Checking active status...
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//!
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//! Building user profile...
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//!
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//! User Profile:
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//! Name: Alice
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//! Age: 30
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//! City: San Francisco
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//! Active: true
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//! ```
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use dagx::{task, DagRunner};
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use futures::FutureExt;
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struct FetchName;
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#[task]
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impl FetchName {
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async fn run() -> String {
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println!("Fetching name...");
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"Alice".to_string()
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}
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}
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struct FetchAge;
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#[task]
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impl FetchAge {
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async fn run() -> i32 {
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println!("Fetching age...");
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30
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}
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}
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struct FetchCity;
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#[task]
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impl FetchCity {
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async fn run() -> String {
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println!("Fetching city...");
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"San Francisco".to_string()
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}
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}
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struct CheckActive;
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#[task]
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impl CheckActive {
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async fn run() -> bool {
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println!("Checking active status...");
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true
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}
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}
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struct BuildProfile;
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#[task]
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impl BuildProfile {
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async fn run(name: &String, age: &i32, city: &String, active: &bool) -> String {
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println!("\nBuilding user profile...");
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format!(
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"User Profile:\n Name: {}\n Age: {}\n City: {}\n Active: {}",
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name, age, city, active
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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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let dag = DagRunner::new();
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// Multiple independent source tasks
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let name = dag.add_task(FetchName);
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let age = dag.add_task(FetchAge);
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let city = dag.add_task(FetchCity);
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let active = dag.add_task(CheckActive);
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// Single downstream task consuming all values
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let profile = dag
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.add_task(BuildProfile)
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.depends_on((&name, &age, &city, &active));
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// Run the DAG
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println!("Running fan-in DAG...\n");
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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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// Print result
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println!("\n{}", dag.get(profile).unwrap());
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}
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