threads2 solution

exercises/20_threads/threads2.rs

@@ -1,35 +1,34 @@
 // Building on the last exercise, we want all of the threads to complete their
-// work but this time the spawned threads need to be in charge of updating a
+// work. But this time, the spawned threads need to be in charge of updating a
-// shared value: JobStatus.jobs_completed
+// shared value: `JobStatus.jobs_done`
 
-use std::sync::Arc;
+use std::{sync::Arc, thread, time::Duration};
-use std::thread;
-use std::time::Duration;
 
 struct JobStatus {
-    jobs_completed: u32,
+    jobs_done: u32,
 }
 
 fn main() {
-    // TODO: `Arc` isn't enough if you want a **mutable** shared state
+    // TODO: `Arc` isn't enough if you want a **mutable** shared state.
-    let status = Arc::new(JobStatus { jobs_completed: 0 });
+    let status = Arc::new(JobStatus { jobs_done: 0 });
 
-    let mut handles = vec![];
+    let mut handles = Vec::new();
     for _ in 0..10 {
         let status_shared = Arc::clone(&status);
         let handle = thread::spawn(move || {
             thread::sleep(Duration::from_millis(250));
-            // TODO: You must take an action before you update a shared value
+
-            status_shared.jobs_completed += 1;
+            // TODO: You must take an action before you update a shared value.
+            status_shared.jobs_done += 1;
         });
         handles.push(handle);
     }
 
-    // Waiting for all jobs to complete
+    // Waiting for all jobs to complete.
     for handle in handles {
         handle.join().unwrap();
     }
 
-    // TODO: Print the value of `JobStatus.jobs_completed`
+    // TODO: Print the value of `JobStatus.jobs_done`.
-    println!("Jobs completed: {}", ???);
+    println!("Jobs done: {}", todo!());
 }

rustlings-macros/info.toml

@@ -1051,19 +1051,19 @@ dir = "20_threads"
 test = false
 hint = """
 `Arc` is an Atomic Reference Counted pointer that allows safe, shared access
-to **immutable** data. But we want to *change* the number of `jobs_completed`
+to **immutable** data. But we want to *change* the number of `jobs_done` so
-so we'll need to also use another type that will only allow one thread to
+we'll need to also use another type that will only allow one thread to mutate
-mutate the data at a time. Take a look at this section of the book:
+the data at a time. Take a look at this section of the book:
 https://doc.rust-lang.org/book/ch16-03-shared-state.html#atomic-reference-counting-with-arct
 
 Keep reading if you'd like more hints :)
 
 Do you now have an `Arc<Mutex<JobStatus>>` at the beginning of `main`? Like:
 ```
-let status = Arc::new(Mutex::new(JobStatus { jobs_completed: 0 }));
+let status = Arc::new(Mutex::new(JobStatus { jobs_done: 0 }));
 ```
 
-Similar to the code in the following example in the book:
+Similar to the code in the following example in The Book:
 https://doc.rust-lang.org/book/ch16-03-shared-state.html#sharing-a-mutext-between-multiple-threads"""
 
 [[exercises]]

solutions/20_threads/threads2.rs

@@ -1 +1,41 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+// Building on the last exercise, we want all of the threads to complete their
+// work. But this time, the spawned threads need to be in charge of updating a
+// shared value: `JobStatus.jobs_done`
+
+use std::{
+    sync::{Arc, Mutex},
+    thread,
+    time::Duration,
+};
+
+struct JobStatus {
+    jobs_done: u32,
+}
+
+fn main() {
+    // `Arc` isn't enough if you want a **mutable** shared state.
+    // We need to wrap the value with a `Mutex`.
+    let status = Arc::new(Mutex::new(JobStatus { jobs_done: 0 }));
+    //                    ^^^^^^^^^^^                          ^
+
+    let mut handles = Vec::new();
+    for _ in 0..10 {
+        let status_shared = Arc::clone(&status);
+        let handle = thread::spawn(move || {
+            thread::sleep(Duration::from_millis(250));
+
+            // Lock before you update a shared value.
+            status_shared.lock().unwrap().jobs_done += 1;
+            //           ^^^^^^^^^^^^^^^^
+        });
+        handles.push(handle);
+    }
+
+    // Waiting for all jobs to complete.
+    for handle in handles {
+        handle.join().unwrap();
+    }
+
+    println!("Jobs done: {}", status.lock().unwrap().jobs_done);
+    //                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+}