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Ben S
77eefe0176
It's more descriptive to call it a cache when there are functions that do all the *actual* OS users stuff separately now. Similarly, we may as well call its constructor 'new' instead of 'empty_cache', because it's obvious that it's a cache now.
61 lines
2.2 KiB
Rust
61 lines
2.2 KiB
Rust
//! This example demonstrates how to use a `UsersCache` cache in a
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//! multi-threaded situation. The cache uses `RefCell`s internally, so it
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//! is distinctly not thread-safe. Instead, you’ll need to place it within
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//! some kind of lock in order to have threads access it one-at-a-time.
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//!
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//! It queries all the users it can find in the range 500..510. This is the
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//! default uid range on my Apple laptop -- Linux starts counting from 1000,
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//! but I can’t include both in the range! It spawns one thread per user to
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//! query, with each thread accessing the same cache.
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//!
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//! Then, afterwards, it retrieves references to the users that had been
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//! cached earlier.
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// For extra fun, try uncommenting some of the lines of code below, making
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// the code try to access the users cache *without* a Mutex, and see it
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// spew compile errors at you.
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extern crate users;
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use users::{Users, UsersCache, uid_t};
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use std::sync::{Arc, Mutex};
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use std::time::Duration;
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use std::thread;
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const LO: uid_t = 500;
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const HI: uid_t = 510;
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fn main() {
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// For thread-safely, our users cache needs to be within a Mutex, so
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// only one thread can access it once. This Mutex needs to be within an
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// Arc, so multiple threads can access the Mutex.
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let cache = Arc::new(Mutex::new(UsersCache::new()));
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// let cache = UsersCache::empty_cache();
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// Loop over the range and query all the users in the range. Although we
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// could use the `&User` values returned, we just ignore them.
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for uid in LO .. HI {
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let cache = cache.clone();
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thread::spawn(move || {
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let cache = cache.lock().unwrap(); // Unlock the mutex
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let _ = cache.get_user_by_uid(uid); // Query our users cache!
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});
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}
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// Wait for all the threads to finish.
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thread::sleep(Duration::from_millis(100));
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// Loop over the same range and print out all the users we find.
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// These users will be retrieved from the cache.
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for uid in LO .. HI {
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let cache = cache.lock().unwrap(); // Re-unlock the mutex
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if let Some(u) = cache.get_user_by_uid(uid) { // Re-query our cache!
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println!("User #{} is {}", u.uid, u.name)
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}
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else {
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println!("User #{} does not exist", uid);
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}
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}
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} |