Vendor dependencies

Let's see how I like this workflow.

vendor/users/examples/threading.rs

@@ -0,0 +1,65 @@
+//! 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 users;
+use users::{Users, UsersCache, uid_t};
+
+extern crate env_logger;
+
+use std::sync::{Arc, Mutex};
+use std::time::Duration;
+use std::thread;
+
+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);
+        }
+    }
+}