rust_waitgroup_implementation.md

Waitgroup Implementation in Rust

While Rust provides tokio::join! and std::sync::Barrier for synchronizing tasks, WaitGroup (available in crossbeam and tokio) offers a lightweight, efficient way to wait for multiple tasks to complete, similar to Go’s sync.WaitGroup.

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Example: Synchronizing Multiple Async Tasks

Using tokio::sync::Notify to implement a simple WaitGroup:

use std::sync::Arc;
use tokio::sync::Notify;
use tokio::task;

struct WaitGroup {
    count: Arc<tokio::sync::Notify>,
}

impl WaitGroup {
    fn new() -> Self {
        Self {
            count: Arc::new(Notify::new()),
        }
    }

    async fn wait(&self) {
        self.count.notified().await;
    }

    fn done(&self) {
        self.count.notify_waiters();
    }
}

#[tokio::main]
async fn main() {
    let wg = WaitGroup::new();
    let wg_clone = wg.clone();

    let handle = task::spawn(async move {
        // Simulate async work
        tokio::time::sleep(std::time::Duration::from_secs(1)).await;
        wg_clone.done();
    });

    wg.wait().await;
    println!("All tasks completed!");

    handle.await.unwrap();
}

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Key Benefits

1. Efficient Task Synchronization: Prevents polling overhead compared to spinning on an atomic counter.
2. Lightweight Alternative to Barrier: Unlike Barrier, it doesn’t require knowing task count upfront.
3. Ideal for Dynamic Workloads: Easily synchronizes a varying number of concurrent async tasks.

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Use Cases

• Parallel Data Processing: Wait for multiple database queries or I/O operations.
• Async Task Pools: Manage concurrent task execution without manual counters.
• Server Shutdown Handling: Ensure graceful shutdown when background workers finish.

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Challenge: Extend this implementation to support reference counting for dynamically spawning and tracking worker tasks. How would you handle cancellations gracefully?