Vendor things

third-party/vendor/crossbeam-utils/src/atomic/mod.rs

@@ -0,0 +1,32 @@
+//! Atomic types.
+//!
+//! * [`AtomicCell`], a thread-safe mutable memory location.
+//! * [`AtomicConsume`], for reading from primitive atomic types with "consume" ordering.
+
+#[cfg(target_has_atomic = "ptr")]
+#[cfg(not(crossbeam_loom))]
+// Use "wide" sequence lock if the pointer width <= 32 for preventing its counter against wrap
+// around.
+//
+// In narrow architectures (pointer width <= 16), the counter is still <= 32-bit and may be
+// vulnerable to wrap around. But it's mostly okay, since in such a primitive hardware, the
+// counter will not be increased that fast.
+// Note that Rust (and C99) pointers must be at least 16-bits: https://github.com/rust-lang/rust/pull/49305
+#[cfg_attr(
+    any(target_pointer_width = "16", target_pointer_width = "32"),
+    path = "seq_lock_wide.rs"
+)]
+mod seq_lock;
+
+#[cfg(target_has_atomic = "ptr")]
+// We cannot provide AtomicCell under cfg(crossbeam_loom) because loom's atomic
+// types have a different in-memory representation than the underlying type.
+// TODO: The latest loom supports fences, so fallback using seqlock may be available.
+#[cfg(not(crossbeam_loom))]
+mod atomic_cell;
+#[cfg(target_has_atomic = "ptr")]
+#[cfg(not(crossbeam_loom))]
+pub use atomic_cell::AtomicCell;
+
+mod consume;
+pub use consume::AtomicConsume;