Worse than fx (despite me hashing the station names there too) better than vanilla

src/main/rust/src/implementations/multi_threaded.rs

@@ -1,3 +1,4 @@
+use crate::models::hasher::CustomBuildHasher;
 use crate::models::station_measurements::StationMeasurements;
 use crate::utils::{hash, parse};
 use std::collections::HashMap;
@@ -12,8 +13,9 @@ pub fn run() {
     const FILE_PATH: &str = "../../../measurements.txt";
     let now = Instant::now();
     thread::scope(|s| {
-        let mut stations: HashMap<u64, (String, StationMeasurements)> =
-            HashMap::with_capacity(DEFAULT_HASHMAP_LENGTH);
+        let hasher = CustomBuildHasher::default();
+        let mut stations: HashMap<u64, (String, StationMeasurements), CustomBuildHasher> =
+            HashMap::with_capacity_and_hasher(DEFAULT_HASHMAP_LENGTH, hasher);
         let (tx, rx) = mpsc::channel();
         let cores = thread::available_parallelism().unwrap().into();
         let file = File::open(FILE_PATH).expect("File measurements.txt not found");
@@ -44,8 +46,9 @@ pub fn run() {
                 let file = File::open(FILE_PATH).expect("File measurements.txt not found");
                 let mut reader = BufReader::new(&file);
                 reader.seek(SeekFrom::Start(currposition)).unwrap();
-                let mut t_stations: HashMap<u64, (String, StationMeasurements)> =
-                    HashMap::with_capacity(DEFAULT_HASHMAP_LENGTH);
+                let hasher = CustomBuildHasher::default();
+                let mut t_stations: HashMap<u64, (String, StationMeasurements), CustomBuildHasher> =
+                    HashMap::with_capacity_and_hasher(DEFAULT_HASHMAP_LENGTH, hasher);
                 let mut line = Vec::with_capacity(108);
                 loop {
                     let line_len = reader

src/main/rust/src/models.rs

@@ -1,2 +1,3 @@
 pub mod mmap;
 pub mod station_measurements;
+pub mod hasher;

src/main/rust/src/models/hasher.rs

@@ -0,0 +1,33 @@
+use std::hash::{BuildHasherDefault, Hasher};
+use crate::utils::hash;
+
+#[derive(Copy, Clone)]
+pub struct CustomHasher(u64);
+
+impl Default for CustomHasher {
+    #[inline]
+    fn default() -> Self {
+        CustomHasher(0)
+    }
+}
+
+impl CustomHasher {
+    #[inline]
+    pub fn with_key(key: u64) -> CustomHasher {
+        CustomHasher(key)
+    }
+}
+
+impl Hasher for CustomHasher {
+    #[inline]
+    fn finish(&self) -> u64 {
+        self.0
+    }
+
+    #[inline]
+    fn write(&mut self, bytes: &[u8]) {
+        *self = CustomHasher(hash::bytes(bytes));
+    }
+}
+
+pub type CustomBuildHasher = BuildHasherDefault<CustomHasher>;