Fix miri test

crossbeam-utils/tests/atomic_cell.rs

@@ -336,8 +336,12 @@ fn issue_748() {
 #[test]
 fn issue_833() {
     use std::num::NonZeroU128;
+    use std::sync::atomic::{AtomicBool, Ordering};
     use std::thread;
 
+    #[cfg(miri)]
+    const N: usize = 10_000;
+    #[cfg(not(miri))]
     const N: usize = 1_000_000;
 
     #[allow(dead_code)]
@@ -350,15 +354,16 @@ fn issue_833() {
         Some(nonzero) => nonzero,
         None => unreachable!(),
     }));
+    static FINISHED: AtomicBool = AtomicBool::new(false);
 
-    thread::spawn(|| {
+    let handle = thread::spawn(|| {
         let cell = match &STATIC {
             Enum::NeverConstructed => unreachable!(),
             Enum::Cell(cell) => cell,
         };
         let x = NonZeroU128::new(0xFFFF_FFFF_FFFF_FFFF_0000_0000_0000_0000).unwrap();
         let y = NonZeroU128::new(0x0000_0000_0000_0000_FFFF_FFFF_FFFF_FFFF).unwrap();
-        loop {
+        while !FINISHED.load(Ordering::Relaxed) {
             cell.store(x);
             cell.store(y);
         }
@@ -369,4 +374,7 @@ fn issue_833() {
             unreachable!(":(");
         }
     }
+
+    FINISHED.store(true, Ordering::Relaxed);
+    handle.join().unwrap();
 }