1 files changed, 93 insertions, 0 deletions
diff --git a/third_party/rust/crossbeam-epoch/src/default.rs b/third_party/rust/crossbeam-epoch/src/default.rs
new file mode 100644
index 0000000000..b42c1c7a7f
--- /dev/null
+++ b/third_party/rust/crossbeam-epoch/src/default.rs
@@ -0,0 +1,93 @@
+//! The default garbage collector.
+//!
+//! For each thread, a participant is lazily initialized on its first use, when the current thread
+//! is registered in the default collector.  If initialized, the thread's participant will get
+//! destructed on thread exit, which in turn unregisters the thread.
+
+use crate::collector::{Collector, LocalHandle};
+use crate::guard::Guard;
+use crate::primitive::thread_local;
+#[cfg(not(crossbeam_loom))]
+use crate::sync::once_lock::OnceLock;
+
+fn collector() -> &'static Collector {
+    #[cfg(not(crossbeam_loom))]
+    {
+        /// The global data for the default garbage collector.
+        static COLLECTOR: OnceLock<Collector> = OnceLock::new();
+        COLLECTOR.get_or_init(Collector::new)
+    }
+    // FIXME: loom does not currently provide the equivalent of Lazy:
+    // https://github.com/tokio-rs/loom/issues/263
+    #[cfg(crossbeam_loom)]
+    {
+        loom::lazy_static! {
+            /// The global data for the default garbage collector.
+            static ref COLLECTOR: Collector = Collector::new();
+        }
+        &COLLECTOR
+    }
+}
+
+thread_local! {
+    /// The per-thread participant for the default garbage collector.
+    static HANDLE: LocalHandle = collector().register();
+}
+
+/// Pins the current thread.
+#[inline]
+pub fn pin() -> Guard {
+    with_handle(|handle| handle.pin())
+}
+
+/// Returns `true` if the current thread is pinned.
+#[inline]
+pub fn is_pinned() -> bool {
+    with_handle(|handle| handle.is_pinned())
+}
+
+/// Returns the default global collector.
+pub fn default_collector() -> &'static Collector {
+    collector()
+}
+
+#[inline]
+fn with_handle<F, R>(mut f: F) -> R
+where
+    F: FnMut(&LocalHandle) -> R,
+{
+    HANDLE
+        .try_with(|h| f(h))
+        .unwrap_or_else(|_| f(&collector().register()))
+}
+
+#[cfg(all(test, not(crossbeam_loom)))]
+mod tests {
+    use crossbeam_utils::thread;
+
+    #[test]
+    fn pin_while_exiting() {
+        struct Foo;
+
+        impl Drop for Foo {
+            fn drop(&mut self) {
+                // Pin after `HANDLE` has been dropped. This must not panic.
+                super::pin();
+            }
+        }
+
+        thread_local! {
+            static FOO: Foo = Foo;
+        }
+
+        thread::scope(|scope| {
+            scope.spawn(|_| {
+                // Initialize `FOO` and then `HANDLE`.
+                FOO.with(|_| ());
+                super::pin();
+                // At thread exit, `HANDLE` gets dropped first and `FOO` second.
+            });
+        })
+        .unwrap();
+    }
+}