fix: split Queue fields and clone sender in threads3.rs (fix #2268)

exercises/20_threads/threads3.rs

@@ -15,20 +15,28 @@ impl Queue {
 }
 
 fn send_tx(q: Queue, tx: mpsc::Sender<u32>) {
-    // TODO: We want to send `tx` to both threads. But currently, it is moved
-    // into the first thread. How could you solve this problem?
+    // Destructure the Queue to move first_half and second_half independently
+    let Queue {
+        first_half,
+        second_half,
+    } = q;
+
+    // Clone the sender so both threads can send to the same receiver
+    let tx1 = tx.clone();
+    let tx2 = tx;
+
     thread::spawn(move || {
-        for val in q.first_half {
+        for val in first_half {
             println!("Sending {val:?}");
-            tx.send(val).unwrap();
+            tx1.send(val).unwrap();
             thread::sleep(Duration::from_millis(250));
         }
     });
 
     thread::spawn(move || {
-        for val in q.second_half {
+        for val in second_half {
             println!("Sending {val:?}");
-            tx.send(val).unwrap();
+            tx2.send(val).unwrap();
             thread::sleep(Duration::from_millis(250));
         }
     });
@@ -57,4 +65,4 @@ mod tests {
         received.sort();
         assert_eq!(received, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
     }
-}
+}