1 files changed, 37 insertions, 0 deletions
diff --git a/components/script_bindings/lock.rs b/components/script_bindings/lock.rs
new file mode 100644
index 00000000000..e8cde2e4087
--- /dev/null
+++ b/components/script_bindings/lock.rs
@@ -0,0 +1,37 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use std::sync::OnceLock;
+
+/// A OnceLock wrapping a type that is not considered threadsafe by the Rust compiler, but
+/// will be used in a threadsafe manner (it will not be mutated, after being initialized).
+///
+/// This is needed to allow using JS API types (which usually involve raw pointers) in static initializers,
+/// when Servo guarantees through the use of OnceLock that only one thread will ever initialize
+/// the value.
+pub struct ThreadUnsafeOnceLock<T>(OnceLock<T>);
+
+impl<T> ThreadUnsafeOnceLock<T> {
+    #[allow(clippy::new_without_default)]
+    pub const fn new() -> Self {
+        Self(OnceLock::new())
+    }
+
+    /// Initialize the value inside this lock. Panics if the lock has been previously initialized.
+    pub fn set(&self, val: T) {
+        assert!(self.0.set(val).is_ok());
+    }
+
+    /// Get a reference to the value inside this lock. Panics if the lock has not been initialized.
+    ///
+    /// # Safety
+    ///   The caller must ensure that it does not mutate value contained inside this lock
+    ///   (using interior mutability).
+    pub unsafe fn get(&self) -> &T {
+        self.0.get().unwrap()
+    }
+}
+
+unsafe impl<T> Sync for ThreadUnsafeOnceLock<T> {}
+unsafe impl<T> Send for ThreadUnsafeOnceLock<T> {}