Vendor things

third-party/vendor/loom/src/sync/notify.rs

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+use crate::rt;
+
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering::SeqCst;
+
+/// Implements the park / unpark pattern directly using Loom's internal
+/// primitives.
+///
+/// Notification establishes an acquire / release synchronization point.
+///
+/// Using this type is useful to mock out constructs when using loom tests.
+#[derive(Debug)]
+pub struct Notify {
+    object: rt::Notify,
+
+    /// Enforces the single waiter invariant
+    waiting: AtomicBool,
+}
+
+impl Notify {
+    /// Create a new `Notify`.
+    pub fn new() -> Notify {
+        Notify {
+            object: rt::Notify::new(false, true),
+            waiting: AtomicBool::new(false),
+        }
+    }
+
+    /// Notify the waiter
+    #[track_caller]
+    pub fn notify(&self) {
+        self.object.notify(location!());
+    }
+
+    /// Wait for a notification
+    #[track_caller]
+    pub fn wait(&self) {
+        self.waiting
+            .compare_exchange(false, true, SeqCst, SeqCst)
+            .expect("only a single thread may wait on `Notify`");
+
+        self.object.wait(location!());
+        self.waiting.store(false, SeqCst);
+    }
+}
+
+impl Default for Notify {
+    fn default() -> Self {
+        Self::new()
+    }
+}