Merge pull request #1929 from mo8it/threads2

threads2: simplify the exercise

exercises/20_threads/threads2.rs

@@ -18,7 +18,9 @@ struct JobStatus {
 }
 
 fn main() {
+    // TODO: `Arc` isn't enough if you want a **mutable** shared state
     let status = Arc::new(JobStatus { jobs_completed: 0 });
+
     let mut handles = vec![];
     for _ in 0..10 {
         let status_shared = Arc::clone(&status);
@@ -29,11 +31,12 @@ fn main() {
         });
         handles.push(handle);
     }
+
+    // Waiting for all jobs to complete
     for handle in handles {
         handle.join().unwrap();
-        // TODO: Print the value of the JobStatus.jobs_completed. Did you notice
-        // anything interesting in the output? Do you have to 'join' on all the
-        // handles?
-        println!("jobs completed {}", ???);
     }
+
+    // TODO: Print the value of `JobStatus.jobs_completed`
+    println!("Jobs completed: {}", ???);
 }

info.toml

@@ -1136,25 +1136,17 @@ to **immutable** data. But we want to *change* the number of `jobs_completed`
 so we'll need to also use another type that will only allow one thread to
 mutate 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
-and keep reading if you'd like more hints :)
 
-Do you now have an `Arc` `Mutex` `JobStatus` at the beginning of main? Like:
+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 }));
 ```
 
-Similar to the code in the example in the book that happens after the text
-that says 'Sharing a Mutex<T> Between Multiple Threads'. If not, give that a
-try! If you do and would like more hints, keep reading!!
-
-Make sure neither of your threads are holding onto the lock of the mutex
-while they are sleeping, since this will prevent the other thread from
-being allowed to get the lock. Locks are automatically released when
-they go out of scope.
-
-If you've learned from the sample solutions, I encourage you to come
-back to this exercise and try it again in a few days to reinforce
-what you've learned :)"""
+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]]
 name = "threads3"