3 files changed, 144 insertions, 0 deletions
diff --git a/solutions/20_threads/threads1.rs b/solutions/20_threads/threads1.rs
new file mode 100644
index 0000000..7f3dd29
--- /dev/null
+++ b/solutions/20_threads/threads1.rs
@@ -0,0 +1,37 @@
+// This program spawns multiple threads that each run for at least 250ms, and
+// each thread returns how much time they took to complete. The program should
+// wait until all the spawned threads have finished and should collect their
+// return values into a vector.
+
+use std::{
+    thread,
+    time::{Duration, Instant},
+};
+
+fn main() {
+    let mut handles = Vec::new();
+    for i in 0..10 {
+        let handle = thread::spawn(move || {
+            let start = Instant::now();
+            thread::sleep(Duration::from_millis(250));
+            println!("Thread {i} done");
+            start.elapsed().as_millis()
+        });
+        handles.push(handle);
+    }
+
+    let mut results = Vec::new();
+    for handle in handles {
+        // Collect the results of all threads into the `results` vector.
+        results.push(handle.join().unwrap());
+    }
+
+    if results.len() != 10 {
+        panic!("Oh no! Some thread isn't done yet!");
+    }
+
+    println!();
+    for (i, result) in results.into_iter().enumerate() {
+        println!("Thread {i} took {result}ms");
+    }
+}
diff --git a/solutions/20_threads/threads2.rs b/solutions/20_threads/threads2.rs
new file mode 100644
index 0000000..bc268d6
--- /dev/null
+++ b/solutions/20_threads/threads2.rs
@@ -0,0 +1,41 @@
+// 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);
+    //                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+}
diff --git a/solutions/20_threads/threads3.rs b/solutions/20_threads/threads3.rs
new file mode 100644
index 0000000..cd2dfbe
--- /dev/null
+++ b/solutions/20_threads/threads3.rs
@@ -0,0 +1,66 @@
+use std::{sync::mpsc, thread, time::Duration};
+
+struct Queue {
+    length: u32,
+    first_half: Vec<u32>,
+    second_half: Vec<u32>,
+}
+
+impl Queue {
+    fn new() -> Self {
+        Self {
+            length: 10,
+            first_half: vec![1, 2, 3, 4, 5],
+            second_half: vec![6, 7, 8, 9, 10],
+        }
+    }
+}
+
+fn send_tx(q: Queue, tx: mpsc::Sender<u32>) {
+    // Clone the sender `tx` first.
+    let tx_clone = tx.clone();
+    thread::spawn(move || {
+        for val in q.first_half {
+            println!("Sending {val:?}");
+            // Then use the clone in the first thread. This means that
+            // `tx_clone` is moved to the first thread and `tx` to the second.
+            tx_clone.send(val).unwrap();
+            thread::sleep(Duration::from_millis(250));
+        }
+    });
+
+    thread::spawn(move || {
+        for val in q.second_half {
+            println!("Sending {val:?}");
+            tx.send(val).unwrap();
+            thread::sleep(Duration::from_millis(250));
+        }
+    });
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn threads3() {
+        let (tx, rx) = mpsc::channel();
+        let queue = Queue::new();
+        let queue_length = queue.length;
+
+        send_tx(queue, tx);
+
+        let mut total_received: u32 = 0;
+        for received in rx {
+            println!("Got: {received}");
+            total_received += 1;
+        }
+
+        println!("Number of received values: {total_received}");
+        assert_eq!(total_received, queue_length);
+    }
+}