1 files changed, 167 insertions, 0 deletions
diff --git a/library/std/tests/sync/lazy_lock.rs b/library/std/tests/sync/lazy_lock.rs
new file mode 100644
index 00000000000..6c14b79f2ce
--- /dev/null
+++ b/library/std/tests/sync/lazy_lock.rs
@@ -0,0 +1,167 @@
+use std::cell::LazyCell;
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering::SeqCst;
+use std::sync::{LazyLock, Mutex, OnceLock};
+use std::{panic, thread};
+
+fn spawn_and_wait<R: Send + 'static>(f: impl FnOnce() -> R + Send + 'static) -> R {
+    thread::spawn(f).join().unwrap()
+}
+
+#[test]
+fn lazy_default() {
+    static CALLED: AtomicUsize = AtomicUsize::new(0);
+
+    struct Foo(u8);
+    impl Default for Foo {
+        fn default() -> Self {
+            CALLED.fetch_add(1, SeqCst);
+            Foo(42)
+        }
+    }
+
+    let lazy: LazyCell<Mutex<Foo>> = <_>::default();
+
+    assert_eq!(CALLED.load(SeqCst), 0);
+
+    assert_eq!(lazy.lock().unwrap().0, 42);
+    assert_eq!(CALLED.load(SeqCst), 1);
+
+    lazy.lock().unwrap().0 = 21;
+
+    assert_eq!(lazy.lock().unwrap().0, 21);
+    assert_eq!(CALLED.load(SeqCst), 1);
+}
+
+#[test]
+#[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
+fn lazy_poisoning() {
+    let x: LazyCell<String> = LazyCell::new(|| panic!("kaboom"));
+    for _ in 0..2 {
+        let res = panic::catch_unwind(panic::AssertUnwindSafe(|| x.len()));
+        assert!(res.is_err());
+    }
+}
+
+#[test]
+#[cfg_attr(any(target_os = "emscripten", target_os = "wasi"), ignore)] // no threads
+fn sync_lazy_new() {
+    static CALLED: AtomicUsize = AtomicUsize::new(0);
+    static SYNC_LAZY: LazyLock<i32> = LazyLock::new(|| {
+        CALLED.fetch_add(1, SeqCst);
+        92
+    });
+
+    assert_eq!(CALLED.load(SeqCst), 0);
+
+    spawn_and_wait(|| {
+        let y = *SYNC_LAZY - 30;
+        assert_eq!(y, 62);
+        assert_eq!(CALLED.load(SeqCst), 1);
+    });
+
+    let y = *SYNC_LAZY - 30;
+    assert_eq!(y, 62);
+    assert_eq!(CALLED.load(SeqCst), 1);
+}
+
+#[test]
+fn sync_lazy_default() {
+    static CALLED: AtomicUsize = AtomicUsize::new(0);
+
+    struct Foo(u8);
+    impl Default for Foo {
+        fn default() -> Self {
+            CALLED.fetch_add(1, SeqCst);
+            Foo(42)
+        }
+    }
+
+    let lazy: LazyLock<Mutex<Foo>> = <_>::default();
+
+    assert_eq!(CALLED.load(SeqCst), 0);
+
+    assert_eq!(lazy.lock().unwrap().0, 42);
+    assert_eq!(CALLED.load(SeqCst), 1);
+
+    lazy.lock().unwrap().0 = 21;
+
+    assert_eq!(lazy.lock().unwrap().0, 21);
+    assert_eq!(CALLED.load(SeqCst), 1);
+}
+
+#[test]
+#[cfg_attr(any(target_os = "emscripten", target_os = "wasi"), ignore)] // no threads
+fn static_sync_lazy() {
+    static XS: LazyLock<Vec<i32>> = LazyLock::new(|| {
+        let mut xs = Vec::new();
+        xs.push(1);
+        xs.push(2);
+        xs.push(3);
+        xs
+    });
+
+    spawn_and_wait(|| {
+        assert_eq!(&*XS, &vec![1, 2, 3]);
+    });
+
+    assert_eq!(&*XS, &vec![1, 2, 3]);
+}
+
+#[test]
+fn static_sync_lazy_via_fn() {
+    fn xs() -> &'static Vec<i32> {
+        static XS: OnceLock<Vec<i32>> = OnceLock::new();
+        XS.get_or_init(|| {
+            let mut xs = Vec::new();
+            xs.push(1);
+            xs.push(2);
+            xs.push(3);
+            xs
+        })
+    }
+    assert_eq!(xs(), &vec![1, 2, 3]);
+}
+
+#[test]
+#[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
+fn sync_lazy_poisoning() {
+    let x: LazyLock<String> = LazyLock::new(|| panic!("kaboom"));
+    for _ in 0..2 {
+        let res = panic::catch_unwind(|| x.len());
+        assert!(res.is_err());
+    }
+}
+
+// Check that we can infer `T` from closure's type.
+#[test]
+fn lazy_type_inference() {
+    let _ = LazyCell::new(|| ());
+}
+
+#[test]
+fn is_sync_send() {
+    fn assert_traits<T: Send + Sync>() {}
+    assert_traits::<LazyLock<String>>();
+}
+
+#[test]
+#[should_panic = "has previously been poisoned"]
+fn lazy_force_mut_panic() {
+    let mut lazy = LazyLock::<String>::new(|| panic!());
+    panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        let _ = LazyLock::force_mut(&mut lazy);
+    }))
+    .unwrap_err();
+    let _ = &*lazy;
+}
+
+#[test]
+fn lazy_force_mut() {
+    let s = "abc".to_owned();
+    let mut lazy = LazyLock::new(move || s);
+    LazyLock::force_mut(&mut lazy);
+    let p = LazyLock::force_mut(&mut lazy);
+    p.clear();
+    LazyLock::force_mut(&mut lazy);
+}