use read_until method instead of custom function because it is faster than mine using the Bytes struct

src/main/rust/src/bin/multi_threaded.rs

@@ -4,10 +4,11 @@ use std::{
     thread,
 };
 use std::collections::HashMap;
-use std::io::{Read, Seek, SeekFrom};
+use std::io::{BufRead, Seek, SeekFrom};
 use std::sync::mpsc;
 use std::time::Instant;
-use onebrc::{parse_line, parse_temp, read_bytes_until};
+
+use onebrc::{parse_line, parse_temp};
 
 const DEFAULT_HASHMAP_LENGTH: usize = 10000;
 
@@ -28,18 +29,9 @@ fn main() {
             let mut reader = BufReader::new(&file);
             let mut byte_start = chunk_length * i;
             reader.seek(SeekFrom::Start(byte_start as u64)).expect("could not seek");
-            let bytes = reader.bytes();
-            for byte in bytes {
-                match byte {
-                    Ok(byte) => {
-                        byte_start += 1;
-                        if byte == b'\n' {
-                            break;
-                        }
-                    }
-                    Err(_) => { panic!("could not go to next") }
-                }
-            }
+            let mut line = Vec::with_capacity(108);
+            let line_len = reader.read_until(b'\n', &mut line).expect("could not read bytes");
+            byte_start += line_len;
             bounds.push(byte_start as u64);
         }
         bounds.push(file_length);
@@ -51,12 +43,14 @@ fn main() {
                 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 bytes = reader.bytes();
-
                 let mut t_stations: HashMap<String, onebrc::StationMeasurements> =
                     HashMap::with_capacity(DEFAULT_HASHMAP_LENGTH);
-
-                while let Some(line) = read_bytes_until(&mut bytes, b'\n') {
+                let mut line = Vec::with_capacity(108);
+                loop {
+                    let line_len = reader.read_until(b'\n', &mut line).expect("could not read bytes");
+                    if line_len == 0 {
+                        break;
+                    }
                     let (station, temp) = parse_line(&line);
                     let station = unsafe { String::from_utf8_unchecked(Vec::from(station)) };
                     let temp = parse_temp(temp);
@@ -76,6 +70,7 @@ fn main() {
                     if currposition >= end {
                         break;
                     }
+                    line.clear();
                 }
                 let _ = tx.send(t_stations);
             });

src/main/rust/src/bin/single_thread.rs

@@ -1,9 +1,9 @@
 use std::collections::HashMap;
 use std::fs::File;
-use std::io::{BufReader, Read};
+use std::io::{BufRead, BufReader};
 use std::time::Instant;
 
-use onebrc::{parse_line, read_bytes_until};
+use onebrc::parse_line;
 
 const DEFAULT_HASHMAP_LENGTH: usize = 10000;
 
@@ -13,8 +13,13 @@ fn main() {
         HashMap::with_capacity(DEFAULT_HASHMAP_LENGTH);
 
     let file = File::open("../../../measurements.txt").expect("File measurements.txt not found");
-    let mut bytes = BufReader::new(&file).bytes();
-    while let Some(line) = read_bytes_until(&mut bytes, b'\n') {
+    let mut reader = BufReader::new(&file);
+    let mut line = Vec::with_capacity(108);
+    loop {
+        let line_len = reader.read_until(b'\n', &mut line).expect("could not read bytes");
+        if line_len == 0 {
+            break;
+        }
         let (station, temp) = parse_line(&line);
         let station = unsafe { String::from_utf8_unchecked(Vec::from(station)) };
         let temp = onebrc::parse_temp(temp);
@@ -30,6 +35,7 @@ fn main() {
             };
             stations.insert(station, measurements);
         }
+        line.clear();
     }
     let mut stations: Vec<String> = stations.iter().map(|(station, measurements)| {
         let measurements = measurements.to_string();

src/main/rust/src/lib.rs

@@ -1,6 +1,4 @@
 use std::fmt::Display;
-use std::fs::File;
-use std::io::{BufReader, Bytes};
 
 #[derive(Copy, Clone)]
 pub struct StationMeasurements {
@@ -68,28 +66,30 @@ pub fn parse_temp(bytes: &[u8]) -> isize {
     }
 }
 
-#[inline]
-pub fn read_bytes_until(bytes: &mut Bytes<BufReader<&File>>, delimiter: u8) -> Option<Vec<u8>> {
-    let mut buf: Vec<u8> = Vec::with_capacity(108);
-    for byte in bytes {
-        if byte.is_err() {
-            panic!("Could not read byte");
-        }
-        let byte = byte.unwrap();
-        if delimiter == byte {
-            return Some(buf);
-        }
-        buf.push(byte);
-    }
-    None
-}
+// using Bytes struct has more performance impact than the std read_until method which uses Vec instead of slice
+// #[inline]
+// pub fn read_bytes_until(bytes: &mut Bytes<BufReader<&File>>, delimiter: u8) -> Option<Vec<u8>> {
+//     let mut buf: Vec<u8> = Vec::with_capacity(108);
+//     for byte in bytes {
+//         if byte.is_err() {
+//             panic!("Could not read byte");
+//         }
+//         let byte = byte.unwrap();
+//         if delimiter == byte {
+//             return Some(buf);
+//         }
+//         buf.push(byte);
+//     }
+//     None
+// }
 
 #[inline]
 pub fn parse_line(line: &[u8]) -> (&[u8], &[u8]) {
     let mut idx = 0;
-    while idx < line.len() && line[idx] != b';' {
+    let line_len = line.len();
+    while idx < line_len && line[idx] != b';' {
         idx += 1;
     }
     let station = &line[0..idx];
-    (station, &line[(idx + 1)..])
+    (station, &line[(idx+1)..(line_len-1)])
 }