Try and use Mutex thing for db

src/file_io.rs

@@ -1,7 +1,10 @@
 extern crate log;
 use crate::user::User;
+use once_cell::sync::Lazy;
+use std::sync::Mutex;
 
 type MyErrorType = Box<dyn std::error::Error>;
+static DB: Lazy<Mutex<sled::Db>> = Lazy::new(|| Mutex::new(sled::Db::open("users_db").unwrap()));
 
 // add a user to the database
 pub fn db_add(user: &User) {
@@ -13,7 +16,7 @@ pub fn db_add(user: &User) {
 
 // write all changed users to database
 pub fn db_write(users_list: &Vec<User>) {
-    let db: sled::Db = sled::open("users_db").unwrap();
+    let db = DB.lock().unwrap();
     for i in users_list {
         let bytes = bincode::serialize(&i).unwrap();
         db.insert(&i.name, bytes).unwrap();
@@ -24,13 +27,13 @@ pub fn db_write(users_list: &Vec<User>) {
 
 // remove a user from the database
 pub fn db_remove(user: &User) {
-    let db: sled::Db = sled::open("users_db").unwrap();
+    let db = DB.lock().unwrap();
     db.remove(&user.name);
 }
 
 // read all users from the database
 pub fn db_read() -> Vec<User> {
-    let db: sled::Db = sled::open("users_db").unwrap();
+    let db = DB.lock().unwrap();
     let mut users: Vec<User> = Vec::new();
     for (_, bytes) in db.iter().filter_map(|r| r.ok()) {
         let read_user: User = bincode::deserialize(&bytes).unwrap();
@@ -42,7 +45,7 @@ pub fn db_read() -> Vec<User> {
 
 // read one user from the database
 pub fn db_read_user(user: &str) -> std::result::Result<Option<User>, MyErrorType> {
-    let db: sled::Db = sled::open("users_db")?;
+    let db = DB.lock().unwrap();
     let entry = db.get(user)?;
     if let Some(user_entry) = entry {
         let read_user: User = bincode::deserialize(&user_entry)?;