1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
|
//! This example demonstrates how to use a `UsersCache` 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 uzers;
use uzers::{uid_t, Users, UsersCache};
extern crate env_logger;
use std::sync::{Arc, Mutex};
use std::thread;
use std::time::Duration;
const LO: uid_t = 500;
const HI: uid_t = 510;
fn main() {
env_logger::init();
// 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(UsersCache::new()));
// let cache = UsersCache::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 = Arc::clone(&cache);
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().to_string_lossy())
} else {
println!("User #{} does not exist", uid);
}
}
}
|
