not working multi threaded solution

rust/src/main.rs

@@ -2,55 +2,72 @@ use std::{
     collections::HashMap,
     fs::File,
     io::{BufRead, BufReader},
+    sync::{Arc, Mutex, MutexGuard},
+    thread,
 };
 
 struct StationMeasurements {
     min: f64,
     max: f64,
-    temps: Vec<f64>,
+    count: usize,
+    sum: f64,
 }
 
 fn main() {
-    let mut stations: HashMap<String, StationMeasurements> = HashMap::new();
+    let stations: Arc<Mutex<HashMap<String, StationMeasurements>>> =
+        Arc::new(Mutex::new(HashMap::new()));
+
+    let cores: usize = std::thread::available_parallelism().unwrap().into();
 
     let file = File::open("../measurements.txt").expect("File measurements.txt not found");
     let reader = BufReader::new(file);
-    let mut line_num = 0;
-    for line_result in reader.lines() {
-        line_num += 1;
-        if line_num % 50000 == 0 {
-            println!("Calculated {line_num} stations");
-        }
-        let line = line_result.expect("could not read line");
-        let (station, temp) = line.split_once(';').unwrap();
-        let temp = temp.parse().unwrap();
-        let measurements_option = stations.get_mut(station);
-        if let Some(measurements) = measurements_option {
-            if temp < measurements.min {
-                measurements.min = temp;
-            } else if temp > measurements.max {
-                measurements.max = temp;
+    let lines = Arc::new(Mutex::new(reader.lines()));
+    let chunk_length = 1_000_000_000 / cores;
+    let mut handles = vec![];
+    for _i in 0..cores {
+        let stations_clone = stations.clone();
+        let lines_clone = lines.clone();
+        let handle = thread::spawn(move || {
+            let lines_guard = lines_clone.lock().unwrap();
+            let chunk = lines_guard.take(chunk_length);
+            lines_guard.skip(chunk_length);
+            for line_result in chunk {
+                let line = line_result.expect("could not read line");
+                let (station, temp) = line.split_once(';').unwrap();
+                let temp = temp.parse().unwrap();
+                let mut stations_guard = stations_clone.lock().unwrap();
+                let measurements_option = stations_guard.get_mut(station);
+                if let Some(measurements) = measurements_option {
+                    if temp < measurements.min {
+                        measurements.min = temp;
+                    } else if temp > measurements.max {
+                        measurements.max = temp;
+                    }
+                    measurements.count += 1;
+                    measurements.sum += temp;
+                } else {
+                    let measurements = StationMeasurements {
+                        min: temp,
+                        max: temp,
+                        count: 1,
+                        sum: temp,
+                    };
+                    stations_clone
+                        .lock()
+                        .unwrap()
+                        .insert(station.to_owned(), measurements);
+                }
             }
-            measurements.temps.push(temp);
-        } else {
-            let measurements = StationMeasurements {
-                min: temp,
-                max: temp,
-                temps: vec![temp],
-            };
-            stations.insert(station.to_owned(), measurements);
-        }
+        });
+        handles.push(handle);
     }
-    for (station, measurments) in stations {
+    for handle in handles {
+        handle.join().unwrap();
+    }
+    for (station, measurments) in stations.lock().unwrap().iter() {
         let min = measurments.min;
         let max = measurments.max;
-        let avg = avg(measurments.temps);
-        println!("{station}={min}/{max}/{avg}");
+        let avg = measurments.sum / measurments.count as f64;
+        println!("{station}={min}/{max}/{avg:.2}");
     }
 }
-
-fn avg(temps: Vec<f64>) -> f64 {
-    let num_temps = temps.len() as f64;
-    let sum_temps: f64 = temps.iter().sum();
-    sum_temps / num_temps
-}