rust 42 lines · 7 steps

Aggregating metrics across threads in Rust

Worker threads tally HTTP statuses into one shared, mutex-guarded struct, then the main thread reclaims it.

Explained by highlit
Intermediate concurrency shared-state mutex thread-pool ownership
1use std::collections::HashMap;
2use std::sync::{Arc, Mutex};
3use std::thread;
4 
5#[derive(Default)]
6struct Metrics {
7 requests: u64,
8 errors: u64,
9 status_counts: HashMap<u16, u64>,
10}
11 
12fn aggregate_responses(statuses: Vec<u16>, workers: usize) -> Metrics {
13 let metrics = Arc::new(Mutex::new(Metrics::default()));
14 let chunk_size = (statuses.len() + workers - 1) / workers;
15 
16 let mut handles = Vec::with_capacity(workers);
17 for chunk in statuses.chunks(chunk_size) {
18 let metrics = Arc::clone(&metrics);
19 let chunk = chunk.to_vec();
20 
21 handles.push(thread::spawn(move || {
22 for status in chunk {
23 let mut m = metrics.lock().unwrap();
24 m.requests += 1;
25 if status >= 400 {
26 m.errors += 1;
27 }
28 *m.status_counts.entry(status).or_insert(0) += 1;
29 }
30 }));
31 }
32 
33 for handle in handles {
34 handle.join().unwrap();
35 }
36 
37 Arc::try_unwrap(metrics)
38 .ok()
39 .expect("all worker threads have finished")
40 .into_inner()
41 .unwrap()
42}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Arc plus Mutex is the standard pattern for safely sharing mutable state across threads.
  2. 2Splitting work into chunks lets you parallelize a flat list across a fixed number of workers.
  3. 3Once all threads join, Arc::try_unwrap recovers sole ownership so you can unwrap the inner value.

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