Simplify pin example slightly

This reduces the vertical space needed by the example, thus making it
easier to keep on the screen while refactoring it.

Author: mgeisler

src/concurrency/async-pitfalls/pin.rs

@@ -1,48 +1,40 @@
+use anyhow::Result;
 use tokio::sync::{mpsc, oneshot};
-use tokio::task::spawn;
 use tokio::time::{sleep, Duration};
 
-// A work item. In this case, just sleep for the given time and respond
-// with a message on the `respond_on` channel.
 #[derive(Debug)]
 struct Work {
     input: u32,
     respond_on: oneshot::Sender<u32>,
 }
 
-// A worker which listens for work on a queue and performs it.
 async fn worker(mut work_queue: mpsc::Receiver<Work>) {
     let mut _iterations = 0;
     loop {
         tokio::select! {
             Some(work) = work_queue.recv() => {
                 sleep(Duration::from_millis(10)).await; // Pretend to work.
-                work.respond_on
-                    .send(work.input * 1000)
-                    .expect("failed to send response");
+                work.respond_on.send(work.input * 1000).unwrap();
                 _iterations += 1;
             }
             // TODO: report number of iterations every 100ms
         }
     }
 }
 
-// A requester which requests work and waits for it to complete.
-async fn do_work(work_queue: &mpsc::Sender<Work>, input: u32) -> u32 {
+async fn do_work(work_queue: &mpsc::Sender<Work>, input: u32) -> Result<u32> {
     let (tx, rx) = oneshot::channel();
-    work_queue
-        .send(Work { input, respond_on: tx })
-        .await
-        .expect("failed to send on work queue");
-    rx.await.expect("failed waiting for response")
+    work_queue.send(Work { input, respond_on: tx }).await?;
+    Ok(rx.await?)
 }
 
 #[tokio::main]
-async fn main() {
+async fn main() -> Result<()> {
     let (tx, rx) = mpsc::channel(10);
-    spawn(worker(rx));
+    tokio::spawn(worker(rx));
     for i in 0..100 {
-        let resp = do_work(&tx, i).await;
+        let resp = do_work(&tx, i).await?;
         println!("work result for iteration {i}: {resp}");
     }
+    Ok(())
 }