Auto merge of #27399 - Gankro:race, r=alexcrichton

r? @alexcrichton

Author: bors

src/doc/tarpl/races.md

@@ -25,7 +25,7 @@ race condition can't violate memory safety in a Rust program on
 its own. Only in conjunction with some other unsafe code can a race condition
 actually violate memory safety. For instance:
 
-```rust
+```rust,norun
 use std::thread;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
@@ -54,6 +54,24 @@ thread::spawn(move || {
 // program execution (panicing is rarely correct) depends on order of
 // thread execution.
 println!("{}", data[idx.load(Ordering::SeqCst)]);
+```
+
+```rust,norun
+use std::thread;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::Arc;
+
+let data = vec![1, 2, 3, 4];
+
+let idx = Arc::new(AtomicUsize::new(0));
+let other_idx = idx.clone();
+
+// `move` captures other_idx by-value, moving it into this thread
+thread::spawn(move || {
+    // It's ok to mutate idx because this value
+    // is an atomic, so it can't cause a Data Race.
+    other_idx.fetch_add(10, Ordering::SeqCst);
+});
 
 if idx.load(Ordering::SeqCst) < data.len() {
     unsafe {