Move some things to `std::sync::poison` and reexport them in `std::sync`

1 files changed, 0 insertions, 729 deletions

diff --git a/library/std/src/sync/rwlock/tests.rs b/library/std/src/sync/rwlock/tests.rs
deleted file mode 100644
index 057c2f1a5d7..00000000000
--- a/library/std/src/sync/rwlock/tests.rs
+++ /dev/null
@@ -1,729 +0,0 @@
-use rand::Rng;
-
-use crate::fmt::Debug;
-use crate::ops::FnMut;
-use crate::panic::{self, AssertUnwindSafe};
-use crate::sync::atomic::{AtomicUsize, Ordering};
-use crate::sync::mpsc::channel;
-use crate::sync::{
-    Arc, MappedRwLockReadGuard, MappedRwLockWriteGuard, RwLock, RwLockReadGuard, RwLockWriteGuard,
-    TryLockError,
-};
-use crate::{hint, mem, thread};
-
-#[derive(Eq, PartialEq, Debug)]
-struct NonCopy(i32);
-
-#[derive(Eq, PartialEq, Debug)]
-struct NonCopyNeedsDrop(i32);
-
-impl Drop for NonCopyNeedsDrop {
-    fn drop(&mut self) {
-        hint::black_box(());
-    }
-}
-
-#[test]
-fn test_needs_drop() {
-    assert!(!mem::needs_drop::<NonCopy>());
-    assert!(mem::needs_drop::<NonCopyNeedsDrop>());
-}
-
-#[derive(Clone, Eq, PartialEq, Debug)]
-struct Cloneable(i32);
-
-#[test]
-fn smoke() {
-    let l = RwLock::new(());
-    drop(l.read().unwrap());
-    drop(l.write().unwrap());
-    drop((l.read().unwrap(), l.read().unwrap()));
-    drop(l.write().unwrap());
-}
-
-#[test]
-// FIXME: On macOS we use a provenance-incorrect implementation and Miri
-// catches that issue with a chance of around 1/1000.
-// See <https://github.com/rust-lang/rust/issues/121950> for details.
-#[cfg_attr(all(miri, target_os = "macos"), ignore)]
-fn frob() {
-    const N: u32 = 10;
-    const M: usize = if cfg!(miri) { 100 } else { 1000 };
-
-    let r = Arc::new(RwLock::new(()));
-
-    let (tx, rx) = channel::<()>();
-    for _ in 0..N {
-        let tx = tx.clone();
-        let r = r.clone();
-        thread::spawn(move || {
-            let mut rng = crate::test_helpers::test_rng();
-            for _ in 0..M {
-                if rng.gen_bool(1.0 / (N as f64)) {
-                    drop(r.write().unwrap());
-                } else {
-                    drop(r.read().unwrap());
-                }
-            }
-            drop(tx);
-        });
-    }
-    drop(tx);
-    let _ = rx.recv();
-}
-
-#[test]
-fn test_rw_arc_poison_wr() {
-    let arc = Arc::new(RwLock::new(1));
-    let arc2 = arc.clone();
-    let _: Result<(), _> = thread::spawn(move || {
-        let _lock = arc2.write().unwrap();
-        panic!();
-    })
-    .join();
-    assert!(arc.read().is_err());
-}
-
-#[test]
-fn test_rw_arc_poison_mapped_w_r() {
-    let arc = Arc::new(RwLock::new(1));
-    let arc2 = arc.clone();
-    let _: Result<(), _> = thread::spawn(move || {
-        let lock = arc2.write().unwrap();
-        let _lock = RwLockWriteGuard::map(lock, |val| val);
-        panic!();
-    })
-    .join();
-    assert!(arc.read().is_err());
-}
-
-#[test]
-fn test_rw_arc_poison_ww() {
-    let arc = Arc::new(RwLock::new(1));
-    assert!(!arc.is_poisoned());
-    let arc2 = arc.clone();
-    let _: Result<(), _> = thread::spawn(move || {
-        let _lock = arc2.write().unwrap();
-        panic!();
-    })
-    .join();
-    assert!(arc.write().is_err());
-    assert!(arc.is_poisoned());
-}
-
-#[test]
-fn test_rw_arc_poison_mapped_w_w() {
-    let arc = Arc::new(RwLock::new(1));
-    let arc2 = arc.clone();
-    let _: Result<(), _> = thread::spawn(move || {
-        let lock = arc2.write().unwrap();
-        let _lock = RwLockWriteGuard::map(lock, |val| val);
-        panic!();
-    })
-    .join();
-    assert!(arc.write().is_err());
-    assert!(arc.is_poisoned());
-}
-
-#[test]
-fn test_rw_arc_no_poison_rr() {
-    let arc = Arc::new(RwLock::new(1));
-    let arc2 = arc.clone();
-    let _: Result<(), _> = thread::spawn(move || {
-        let _lock = arc2.read().unwrap();
-        panic!();
-    })
-    .join();
-    let lock = arc.read().unwrap();
-    assert_eq!(*lock, 1);
-}
-
-#[test]
-fn test_rw_arc_no_poison_mapped_r_r() {
-    let arc = Arc::new(RwLock::new(1));
-    let arc2 = arc.clone();
-    let _: Result<(), _> = thread::spawn(move || {
-        let lock = arc2.read().unwrap();
-        let _lock = RwLockReadGuard::map(lock, |val| val);
-        panic!();
-    })
-    .join();
-    let lock = arc.read().unwrap();
-    assert_eq!(*lock, 1);
-}
-
-#[test]
-fn test_rw_arc_no_poison_rw() {
-    let arc = Arc::new(RwLock::new(1));
-    let arc2 = arc.clone();
-    let _: Result<(), _> = thread::spawn(move || {
-        let _lock = arc2.read().unwrap();
-        panic!()
-    })
-    .join();
-    let lock = arc.write().unwrap();
-    assert_eq!(*lock, 1);
-}
-
-#[test]
-fn test_rw_arc_no_poison_mapped_r_w() {
-    let arc = Arc::new(RwLock::new(1));
-    let arc2 = arc.clone();
-    let _: Result<(), _> = thread::spawn(move || {
-        let lock = arc2.read().unwrap();
-        let _lock = RwLockReadGuard::map(lock, |val| val);
-        panic!();
-    })
-    .join();
-    let lock = arc.write().unwrap();
-    assert_eq!(*lock, 1);
-}
-
-#[test]
-fn test_rw_arc() {
-    let arc = Arc::new(RwLock::new(0));
-    let arc2 = arc.clone();
-    let (tx, rx) = channel();
-
-    thread::spawn(move || {
-        let mut lock = arc2.write().unwrap();
-        for _ in 0..10 {
-            let tmp = *lock;
-            *lock = -1;
-            thread::yield_now();
-            *lock = tmp + 1;
-        }
-        tx.send(()).unwrap();
-    });
-
-    // Readers try to catch the writer in the act
-    let mut children = Vec::new();
-    for _ in 0..5 {
-        let arc3 = arc.clone();
-        children.push(thread::spawn(move || {
-            let lock = arc3.read().unwrap();
-            assert!(*lock >= 0);
-        }));
-    }
-
-    // Wait for children to pass their asserts
-    for r in children {
-        assert!(r.join().is_ok());
-    }
-
-    // Wait for writer to finish
-    rx.recv().unwrap();
-    let lock = arc.read().unwrap();
-    assert_eq!(*lock, 10);
-}
-
-#[test]
-fn test_rw_arc_access_in_unwind() {
-    let arc = Arc::new(RwLock::new(1));
-    let arc2 = arc.clone();
-    let _ = thread::spawn(move || -> () {
-        struct Unwinder {
-            i: Arc<RwLock<isize>>,
-        }
-        impl Drop for Unwinder {
-            fn drop(&mut self) {
-                let mut lock = self.i.write().unwrap();
-                *lock += 1;
-            }
-        }
-        let _u = Unwinder { i: arc2 };
-        panic!();
-    })
-    .join();
-    let lock = arc.read().unwrap();
-    assert_eq!(*lock, 2);
-}
-
-#[test]
-fn test_rwlock_unsized() {
-    let rw: &RwLock<[i32]> = &RwLock::new([1, 2, 3]);
-    {
-        let b = &mut *rw.write().unwrap();
-        b[0] = 4;
-        b[2] = 5;
-    }
-    let comp: &[i32] = &[4, 2, 5];
-    assert_eq!(&*rw.read().unwrap(), comp);
-}
-
-#[test]
-fn test_rwlock_try_write() {
-    let lock = RwLock::new(0isize);
-    let read_guard = lock.read().unwrap();
-
-    let write_result = lock.try_write();
-    match write_result {
-        Err(TryLockError::WouldBlock) => (),
-        Ok(_) => assert!(false, "try_write should not succeed while read_guard is in scope"),
-        Err(_) => assert!(false, "unexpected error"),
-    }
-
-    drop(read_guard);
-    let mapped_read_guard = RwLockReadGuard::map(lock.read().unwrap(), |_| &());
-
-    let write_result = lock.try_write();
-    match write_result {
-        Err(TryLockError::WouldBlock) => (),
-        Ok(_) => assert!(false, "try_write should not succeed while mapped_read_guard is in scope"),
-        Err(_) => assert!(false, "unexpected error"),
-    }
-
-    drop(mapped_read_guard);
-}
-
-fn new_poisoned_rwlock<T>(value: T) -> RwLock<T> {
-    let lock = RwLock::new(value);
-
-    let catch_unwind_result = panic::catch_unwind(AssertUnwindSafe(|| {
-        let _guard = lock.write().unwrap();
-
-        panic!("test panic to poison RwLock");
-    }));
-
-    assert!(catch_unwind_result.is_err());
-    assert!(lock.is_poisoned());
-
-    lock
-}
-
-#[test]
-fn test_into_inner() {
-    let m = RwLock::new(NonCopy(10));
-    assert_eq!(m.into_inner().unwrap(), NonCopy(10));
-}
-
-#[test]
-fn test_into_inner_drop() {
-    struct Foo(Arc<AtomicUsize>);
-    impl Drop for Foo {
-        fn drop(&mut self) {
-            self.0.fetch_add(1, Ordering::SeqCst);
-        }
-    }
-    let num_drops = Arc::new(AtomicUsize::new(0));
-    let m = RwLock::new(Foo(num_drops.clone()));
-    assert_eq!(num_drops.load(Ordering::SeqCst), 0);
-    {
-        let _inner = m.into_inner().unwrap();
-        assert_eq!(num_drops.load(Ordering::SeqCst), 0);
-    }
-    assert_eq!(num_drops.load(Ordering::SeqCst), 1);
-}
-
-#[test]
-fn test_into_inner_poison() {
-    let m = new_poisoned_rwlock(NonCopy(10));
-
-    match m.into_inner() {
-        Err(e) => assert_eq!(e.into_inner(), NonCopy(10)),
-        Ok(x) => panic!("into_inner of poisoned RwLock is Ok: {x:?}"),
-    }
-}
-
-#[test]
-fn test_get_cloned() {
-    let m = RwLock::new(Cloneable(10));
-
-    assert_eq!(m.get_cloned().unwrap(), Cloneable(10));
-}
-
-#[test]
-fn test_get_cloned_poison() {
-    let m = new_poisoned_rwlock(Cloneable(10));
-
-    match m.get_cloned() {
-        Err(e) => assert_eq!(e.into_inner(), ()),
-        Ok(x) => panic!("get of poisoned RwLock is Ok: {x:?}"),
-    }
-}
-
-#[test]
-fn test_get_mut() {
-    let mut m = RwLock::new(NonCopy(10));
-    *m.get_mut().unwrap() = NonCopy(20);
-    assert_eq!(m.into_inner().unwrap(), NonCopy(20));
-}
-
-#[test]
-fn test_get_mut_poison() {
-    let mut m = new_poisoned_rwlock(NonCopy(10));
-
-    match m.get_mut() {
-        Err(e) => assert_eq!(*e.into_inner(), NonCopy(10)),
-        Ok(x) => panic!("get_mut of poisoned RwLock is Ok: {x:?}"),
-    }
-}
-
-#[test]
-fn test_set() {
-    fn inner<T>(mut init: impl FnMut() -> T, mut value: impl FnMut() -> T)
-    where
-        T: Debug + Eq,
-    {
-        let m = RwLock::new(init());
-
-        assert_eq!(*m.read().unwrap(), init());
-        m.set(value()).unwrap();
-        assert_eq!(*m.read().unwrap(), value());
-    }
-
-    inner(|| NonCopy(10), || NonCopy(20));
-    inner(|| NonCopyNeedsDrop(10), || NonCopyNeedsDrop(20));
-}
-
-#[test]
-fn test_set_poison() {
-    fn inner<T>(mut init: impl FnMut() -> T, mut value: impl FnMut() -> T)
-    where
-        T: Debug + Eq,
-    {
-        let m = new_poisoned_rwlock(init());
-
-        match m.set(value()) {
-            Err(e) => {
-                assert_eq!(e.into_inner(), value());
-                assert_eq!(m.into_inner().unwrap_err().into_inner(), init());
-            }
-            Ok(x) => panic!("set of poisoned RwLock is Ok: {x:?}"),
-        }
-    }
-
-    inner(|| NonCopy(10), || NonCopy(20));
-    inner(|| NonCopyNeedsDrop(10), || NonCopyNeedsDrop(20));
-}
-
-#[test]
-fn test_replace() {
-    fn inner<T>(mut init: impl FnMut() -> T, mut value: impl FnMut() -> T)
-    where
-        T: Debug + Eq,
-    {
-        let m = RwLock::new(init());
-
-        assert_eq!(*m.read().unwrap(), init());
-        assert_eq!(m.replace(value()).unwrap(), init());
-        assert_eq!(*m.read().unwrap(), value());
-    }
-
-    inner(|| NonCopy(10), || NonCopy(20));
-    inner(|| NonCopyNeedsDrop(10), || NonCopyNeedsDrop(20));
-}
-
-#[test]
-fn test_replace_poison() {
-    fn inner<T>(mut init: impl FnMut() -> T, mut value: impl FnMut() -> T)
-    where
-        T: Debug + Eq,
-    {
-        let m = new_poisoned_rwlock(init());
-
-        match m.replace(value()) {
-            Err(e) => {
-                assert_eq!(e.into_inner(), value());
-                assert_eq!(m.into_inner().unwrap_err().into_inner(), init());
-            }
-            Ok(x) => panic!("replace of poisoned RwLock is Ok: {x:?}"),
-        }
-    }
-
-    inner(|| NonCopy(10), || NonCopy(20));
-    inner(|| NonCopyNeedsDrop(10), || NonCopyNeedsDrop(20));
-}
-
-#[test]
-fn test_read_guard_covariance() {
-    fn do_stuff<'a>(_: RwLockReadGuard<'_, &'a i32>, _: &'a i32) {}
-    let j: i32 = 5;
-    let lock = RwLock::new(&j);
-    {
-        let i = 6;
-        do_stuff(lock.read().unwrap(), &i);
-    }
-    drop(lock);
-}
-
-#[test]
-fn test_mapped_read_guard_covariance() {
-    fn do_stuff<'a>(_: MappedRwLockReadGuard<'_, &'a i32>, _: &'a i32) {}
-    let j: i32 = 5;
-    let lock = RwLock::new((&j, &j));
-    {
-        let i = 6;
-        let guard = lock.read().unwrap();
-        let guard = RwLockReadGuard::map(guard, |(val, _val)| val);
-        do_stuff(guard, &i);
-    }
-    drop(lock);
-}
-
-#[test]
-fn test_mapping_mapped_guard() {
-    let arr = [0; 4];
-    let mut lock = RwLock::new(arr);
-    let guard = lock.write().unwrap();
-    let guard = RwLockWriteGuard::map(guard, |arr| &mut arr[..2]);
-    let mut guard = MappedRwLockWriteGuard::map(guard, |slice| &mut slice[1..]);
-    assert_eq!(guard.len(), 1);
-    guard[0] = 42;
-    drop(guard);
-    assert_eq!(*lock.get_mut().unwrap(), [0, 42, 0, 0]);
-
-    let guard = lock.read().unwrap();
-    let guard = RwLockReadGuard::map(guard, |arr| &arr[..2]);
-    let guard = MappedRwLockReadGuard::map(guard, |slice| &slice[1..]);
-    assert_eq!(*guard, [42]);
-    drop(guard);
-    assert_eq!(*lock.get_mut().unwrap(), [0, 42, 0, 0]);
-}
-
-#[test]
-fn panic_while_mapping_read_unlocked_no_poison() {
-    let lock = RwLock::new(());
-
-    let _ = panic::catch_unwind(|| {
-        let guard = lock.read().unwrap();
-        let _guard = RwLockReadGuard::map::<(), _>(guard, |_| panic!());
-    });
-
-    match lock.try_write() {
-        Ok(_) => {}
-        Err(TryLockError::WouldBlock) => {
-            panic!("panicking in a RwLockReadGuard::map closure should release the read lock")
-        }
-        Err(TryLockError::Poisoned(_)) => {
-            panic!("panicking in a RwLockReadGuard::map closure should not poison the RwLock")
-        }
-    }
-
-    let _ = panic::catch_unwind(|| {
-        let guard = lock.read().unwrap();
-        let _guard = RwLockReadGuard::try_map::<(), _>(guard, |_| panic!());
-    });
-
-    match lock.try_write() {
-        Ok(_) => {}
-        Err(TryLockError::WouldBlock) => {
-            panic!("panicking in a RwLockReadGuard::try_map closure should release the read lock")
-        }
-        Err(TryLockError::Poisoned(_)) => {
-            panic!("panicking in a RwLockReadGuard::try_map closure should not poison the RwLock")
-        }
-    }
-
-    let _ = panic::catch_unwind(|| {
-        let guard = lock.read().unwrap();
-        let guard = RwLockReadGuard::map::<(), _>(guard, |val| val);
-        let _guard = MappedRwLockReadGuard::map::<(), _>(guard, |_| panic!());
-    });
-
-    match lock.try_write() {
-        Ok(_) => {}
-        Err(TryLockError::WouldBlock) => {
-            panic!("panicking in a MappedRwLockReadGuard::map closure should release the read lock")
-        }
-        Err(TryLockError::Poisoned(_)) => {
-            panic!("panicking in a MappedRwLockReadGuard::map closure should not poison the RwLock")
-        }
-    }
-
-    let _ = panic::catch_unwind(|| {
-        let guard = lock.read().unwrap();
-        let guard = RwLockReadGuard::map::<(), _>(guard, |val| val);
-        let _guard = MappedRwLockReadGuard::try_map::<(), _>(guard, |_| panic!());
-    });
-
-    match lock.try_write() {
-        Ok(_) => {}
-        Err(TryLockError::WouldBlock) => panic!(
-            "panicking in a MappedRwLockReadGuard::try_map closure should release the read lock"
-        ),
-        Err(TryLockError::Poisoned(_)) => panic!(
-            "panicking in a MappedRwLockReadGuard::try_map closure should not poison the RwLock"
-        ),
-    }
-
-    drop(lock);
-}
-
-#[test]
-fn panic_while_mapping_write_unlocked_poison() {
-    let lock = RwLock::new(());
-
-    let _ = panic::catch_unwind(|| {
-        let guard = lock.write().unwrap();
-        let _guard = RwLockWriteGuard::map::<(), _>(guard, |_| panic!());
-    });
-
-    match lock.try_write() {
-        Ok(_) => panic!("panicking in a RwLockWriteGuard::map closure should poison the RwLock"),
-        Err(TryLockError::WouldBlock) => {
-            panic!("panicking in a RwLockWriteGuard::map closure should release the write lock")
-        }
-        Err(TryLockError::Poisoned(_)) => {}
-    }
-
-    let _ = panic::catch_unwind(|| {
-        let guard = lock.write().unwrap();
-        let _guard = RwLockWriteGuard::try_map::<(), _>(guard, |_| panic!());
-    });
-
-    match lock.try_write() {
-        Ok(_) => {
-            panic!("panicking in a RwLockWriteGuard::try_map closure should poison the RwLock")
-        }
-        Err(TryLockError::WouldBlock) => {
-            panic!("panicking in a RwLockWriteGuard::try_map closure should release the write lock")
-        }
-        Err(TryLockError::Poisoned(_)) => {}
-    }
-
-    let _ = panic::catch_unwind(|| {
-        let guard = lock.write().unwrap();
-        let guard = RwLockWriteGuard::map::<(), _>(guard, |val| val);
-        let _guard = MappedRwLockWriteGuard::map::<(), _>(guard, |_| panic!());
-    });
-
-    match lock.try_write() {
-        Ok(_) => {
-            panic!("panicking in a MappedRwLockWriteGuard::map closure should poison the RwLock")
-        }
-        Err(TryLockError::WouldBlock) => panic!(
-            "panicking in a MappedRwLockWriteGuard::map closure should release the write lock"
-        ),
-        Err(TryLockError::Poisoned(_)) => {}
-    }
-
-    let _ = panic::catch_unwind(|| {
-        let guard = lock.write().unwrap();
-        let guard = RwLockWriteGuard::map::<(), _>(guard, |val| val);
-        let _guard = MappedRwLockWriteGuard::try_map::<(), _>(guard, |_| panic!());
-    });
-
-    match lock.try_write() {
-        Ok(_) => panic!(
-            "panicking in a MappedRwLockWriteGuard::try_map closure should poison the RwLock"
-        ),
-        Err(TryLockError::WouldBlock) => panic!(
-            "panicking in a MappedRwLockWriteGuard::try_map closure should release the write lock"
-        ),
-        Err(TryLockError::Poisoned(_)) => {}
-    }
-
-    drop(lock);
-}
-
-#[test]
-fn test_downgrade_basic() {
-    let r = RwLock::new(());
-
-    let write_guard = r.write().unwrap();
-    let _read_guard = RwLockWriteGuard::downgrade(write_guard);
-}
-
-#[test]
-// FIXME: On macOS we use a provenance-incorrect implementation and Miri catches that issue.
-// See <https://github.com/rust-lang/rust/issues/121950> for details.
-#[cfg_attr(all(miri, target_os = "macos"), ignore)]
-fn test_downgrade_observe() {
-    // Taken from the test `test_rwlock_downgrade` from:
-    // https://github.com/Amanieu/parking_lot/blob/master/src/rwlock.rs
-
-    const W: usize = 20;
-    const N: usize = if cfg!(miri) { 40 } else { 100 };
-
-    // This test spawns `W` writer threads, where each will increment a counter `N` times, ensuring
-    // that the value they wrote has not changed after downgrading.
-
-    let rw = Arc::new(RwLock::new(0));
-
-    // Spawn the writers that will do `W * N` operations and checks.
-    let handles: Vec<_> = (0..W)
-        .map(|_| {
-            let rw = rw.clone();
-            thread::spawn(move || {
-                for _ in 0..N {
-                    // Increment the counter.
-                    let mut write_guard = rw.write().unwrap();
-                    *write_guard += 1;
-                    let cur_val = *write_guard;
-
-                    // Downgrade the lock to read mode, where the value protected cannot be modified.
-                    let read_guard = RwLockWriteGuard::downgrade(write_guard);
-                    assert_eq!(cur_val, *read_guard);
-                }
-            })
-        })
-        .collect();
-
-    for handle in handles {
-        handle.join().unwrap();
-    }
-
-    assert_eq!(*rw.read().unwrap(), W * N);
-}
-
-#[test]
-// FIXME: On macOS we use a provenance-incorrect implementation and Miri catches that issue.
-// See <https://github.com/rust-lang/rust/issues/121950> for details.
-#[cfg_attr(all(miri, target_os = "macos"), ignore)]
-fn test_downgrade_atomic() {
-    const NEW_VALUE: i32 = -1;
-
-    // This test checks that `downgrade` is atomic, meaning as soon as a write lock has been
-    // downgraded, the lock must be in read mode and no other threads can take the write lock to
-    // modify the protected value.
-
-    // `W` is the number of evil writer threads.
-    const W: usize = 20;
-    let rwlock = Arc::new(RwLock::new(0));
-
-    // Spawns many evil writer threads that will try and write to the locked value before the
-    // initial writer (who has the exclusive lock) can read after it downgrades.
-    // If the `RwLock` behaves correctly, then the initial writer should read the value it wrote
-    // itself as no other thread should be able to mutate the protected value.
-
-    // Put the lock in write mode, causing all future threads trying to access this go to sleep.
-    let mut main_write_guard = rwlock.write().unwrap();
-
-    // Spawn all of the evil writer threads. They will each increment the protected value by 1.
-    let handles: Vec<_> = (0..W)
-        .map(|_| {
-            let rwlock = rwlock.clone();
-            thread::spawn(move || {
-                // Will go to sleep since the main thread initially has the write lock.
-                let mut evil_guard = rwlock.write().unwrap();
-                *evil_guard += 1;
-            })
-        })
-        .collect();
-
-    // Wait for a good amount of time so that evil threads go to sleep.
-    // Note: this is not strictly necessary...
-    let eternity = crate::time::Duration::from_millis(42);
-    thread::sleep(eternity);
-
-    // Once everyone is asleep, set the value to `NEW_VALUE`.
-    *main_write_guard = NEW_VALUE;
-
-    // Atomically downgrade the write guard into a read guard.
-    let main_read_guard = RwLockWriteGuard::downgrade(main_write_guard);
-
-    // If the above is not atomic, then it would be possible for an evil thread to get in front of
-    // this read and change the value to be non-negative.
-    assert_eq!(*main_read_guard, NEW_VALUE, "`downgrade` was not atomic");
-
-    // Drop the main read guard and allow the evil writer threads to start incrementing.
-    drop(main_read_guard);
-
-    for handle in handles {
-        handle.join().unwrap();
-    }
-
-    let final_check = rwlock.read().unwrap();
-    assert_eq!(*final_check, W as i32 + NEW_VALUE);
-}