feat: Adding threads1.rs with a focus on JoinHandles and waiting for

spawned threads to finish. Moved the original threads1.rs to threads2.rs
with the focus on the Mutex and modifying shared data. #892

info.toml

@@ -878,6 +878,22 @@ name = "threads1"
 path = "exercises/threads/threads1.rs"
 mode = "compile"
 hint = """
+`JoinHandle` is a struct that is returned from a spawned thread: 
+https://doc.rust-lang.org/std/thread/fn.spawn.html
+
+A challenge with multi-threaded applications is that the main thread can 
+finish before the spawned threads are completed.
+https://doc.rust-lang.org/book/ch16-01-threads.html#waiting-for-all-threads-to-finish-using-join-handle
+
+Collect the JoinHandles and wait for them to finish.
+https://doc.rust-lang.org/std/thread/struct.JoinHandle.html
+"""
+
+[[exercises]]
+name = "threads2"
+path = "exercises/threads/threads2.rs"
+mode = "compile"
+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`
 so we'll need to also use another type that will only allow one thread to
@@ -898,14 +914,6 @@ 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.
 
-Ok, so, real talk, this was actually tricky for *me* to do too. And
-I could see a lot of different problems you might run into, so at this
-point I'm not sure which one you've hit :)
-
-Please open an issue if you're still running into a problem that
-these hints are not helping you with, or if you've looked at the sample
-answers and don't understand why they work and yours doesn't.
-
 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 :)"""