You've already forked rust-users
mirror of
https://github.com/uutils/rust-users.git
synced 2026-06-10 15:48:37 -07:00
Benjamin Sago
aa94ee89db
The primary goal of this commit was to avoid having to clone the users and groups it produces. The old implementation was written by me when I hadn't *fully* internalised how lifetimes worked, and just used `clone` to get around the error messages. It was only later that I realised how inefficient this actually is -- the values stored in the cache are never used, only their clones are! Several attempt at this later, I settled on using `Arc` for everything and cloning *those* values instead. All the gory details of what happened are written in a comment in the OS module. The short version is that it's now possible to change the `Users` trait's methods from taking `&mut self` to just taking `&self`. This is within the allowed uses of `Cell`: implementation details of a method that does actually return the same thing each time, which this is. The main casualty is that the user now has to know about `Arc` and initialise a user with a username in such a container, which I hope to solve in a later commit.
61 lines
2.2 KiB
Rust
61 lines
2.2 KiB
Rust
//! This example demonstrates how to use an `OSUsers` cache in a
|
||
//! multi-threaded situation. The cache uses `RefCell`s internally, so it
|
||
//! is distinctly not thread-safe. Instead, you’ll need to place it within
|
||
//! some kind of lock in order to have threads access it one-at-a-time.
|
||
//!
|
||
//! It queries all the users it can find in the range 500..510. This is the
|
||
//! default uid range on my Apple laptop -- Linux starts counting from 1000,
|
||
//! but I can’t include both in the range! It spawns one thread per user to
|
||
//! query, with each thread accessing the same cache.
|
||
//!
|
||
//! Then, afterwards, it retrieves references to the users that had been
|
||
//! cached earlier.
|
||
|
||
// For extra fun, try uncommenting some of the lines of code below, making
|
||
// the code try to access the users cache *without* a Mutex, and see it
|
||
// spew compile errors at you.
|
||
|
||
extern crate users;
|
||
use users::{Users, OSUsers, uid_t};
|
||
|
||
use std::sync::{Arc, Mutex};
|
||
use std::time::Duration;
|
||
use std::thread;
|
||
|
||
const LO: uid_t = 500;
|
||
const HI: uid_t = 510;
|
||
|
||
fn main() {
|
||
|
||
// For thread-safely, our users cache needs to be within a Mutex, so
|
||
// only one thread can access it once. This Mutex needs to be within an
|
||
// Arc, so multiple threads can access the Mutex.
|
||
let cache = Arc::new(Mutex::new(OSUsers::empty_cache()));
|
||
// let cache = OSUsers::empty_cache();
|
||
|
||
// Loop over the range and query all the users in the range. Although we
|
||
// could use the `&User` values returned, we just ignore them.
|
||
for uid in LO .. HI {
|
||
let cache = cache.clone();
|
||
|
||
thread::spawn(move || {
|
||
let cache = cache.lock().unwrap(); // Unlock the mutex
|
||
let _ = cache.get_user_by_uid(uid); // Query our users cache!
|
||
});
|
||
}
|
||
|
||
// Wait for all the threads to finish.
|
||
thread::sleep(Duration::from_millis(100));
|
||
|
||
// Loop over the same range and print out all the users we find.
|
||
// These users will be retrieved from the cache.
|
||
for uid in LO .. HI {
|
||
let cache = cache.lock().unwrap(); // Re-unlock the mutex
|
||
if let Some(u) = cache.get_user_by_uid(uid) { // Re-query our cache!
|
||
println!("User #{} is {}", u.uid, u.name)
|
||
}
|
||
else {
|
||
println!("User #{} does not exist", uid);
|
||
}
|
||
}
|
||
} |