doc test: fix mpsc.rs try_send doc test

Signed-off-by: Eval EXEC <[email protected]>

Author: eval-exec

library/std/src/sync/mpsc.rs

@@ -689,39 +689,28 @@ impl<T> SyncSender<T> {
     /// # Examples
     ///
     /// ```rust
-    /// use std::sync::mpsc::sync_channel;
-    /// use std::thread;
+    /// use std::sync::mpsc::{sync_channel, TrySendError};
     ///
     /// // Create a sync_channel with buffer size 1
-    /// let (sync_sender, receiver) = sync_channel(1);
-    /// let sync_sender2 = sync_sender.clone();
+    /// let (sender, receiver) = sync_channel(1);
     ///
-    /// // First thread owns sync_sender
-    /// thread::spawn(move || {
-    ///     sync_sender.send(1).unwrap();
-    ///     sync_sender.send(2).unwrap();
-    ///     // Thread blocked
-    /// });
+    /// // First send succeeds immediately
+    /// assert!(sender.try_send(1).is_ok());
     ///
-    /// // Second thread owns sync_sender2
-    /// thread::spawn(move || {
-    ///     // This will return an error and send
-    ///     // no message if the buffer is full
-    ///     let _ = sync_sender2.try_send(3);
-    /// });
-    ///
-    /// let mut msg;
-    /// msg = receiver.recv().unwrap();
-    /// println!("message {msg} received");
+    /// // Second send fails because buffer is full
+    /// match sender.try_send(2) {
+    ///     Err(TrySendError::Full(2)) => {
+    ///         println!("Channel buffer is full, couldn't send 2");
+    ///     }
+    ///     _ => unreachable!(),
+    /// }
     ///
-    /// msg = receiver.recv().unwrap();
-    /// println!("message {msg} received");
+    /// // After receiving, buffer has space again
+    /// let received = receiver.recv().unwrap();
+    /// assert_eq!(received, 1);
     ///
-    /// // Third message may have never been sent
-    /// match receiver.try_recv() {
-    ///     Ok(msg) => println!("message {msg} received"),
-    ///     Err(_) => println!("the third message was never sent"),
-    /// }
+    /// // Now try_send succeeds again
+    /// assert!(sender.try_send(3).is_ok());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn try_send(&self, t: T) -> Result<(), TrySendError<T>> {