1 files changed, 84 insertions, 0 deletions
diff --git a/components/layout/flow_ref.rs b/components/layout/flow_ref.rs
new file mode 100644
index 00000000000..d90d9ac4cc0
--- /dev/null
+++ b/components/layout/flow_ref.rs
@@ -0,0 +1,84 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+/// Reference-counted pointers to flows.
+///
+/// Eventually, with dynamically sized types in Rust, much of this code will be superfluous.
+
+use flow::Flow;
+use flow;
+
+use std::mem;
+use std::ptr;
+use std::raw;
+use std::sync::atomics::SeqCst;
+
+#[unsafe_no_drop_flag]
+pub struct FlowRef {
+    object: raw::TraitObject,
+}
+
+impl FlowRef {
+    pub fn new(mut flow: Box<Flow>) -> FlowRef {
+        unsafe {
+            let result = {
+                let flow_ref: &mut Flow = flow;
+                let object = mem::transmute::<&mut Flow, raw::TraitObject>(flow_ref);
+                FlowRef { object: object }
+            };
+            mem::forget(flow);
+            result
+        }
+    }
+
+    pub fn get<'a>(&'a self) -> &'a Flow {
+        unsafe {
+            mem::transmute_copy::<raw::TraitObject, &'a Flow>(&self.object)
+        }
+    }
+
+    pub fn get_mut<'a>(&'a mut self) -> &'a mut Flow {
+        unsafe {
+            mem::transmute_copy::<raw::TraitObject, &'a mut Flow>(&self.object)
+        }
+    }
+}
+
+impl Drop for FlowRef {
+    fn drop(&mut self) {
+        unsafe {
+            if self.object.vtable.is_null() {
+                return
+            }
+            if flow::base(self.get()).ref_count().fetch_sub(1, SeqCst) > 1 {
+                return
+            }
+            let flow_ref: FlowRef = mem::replace(self, FlowRef {
+                object: raw::TraitObject {
+                    vtable: ptr::mut_null(),
+                    data: ptr::mut_null(),
+                }
+            });
+            drop(mem::transmute::<raw::TraitObject, Box<Flow>>(flow_ref.object));
+            mem::forget(flow_ref);
+            self.object.vtable = ptr::mut_null();
+            self.object.data = ptr::mut_null();
+        }
+    }
+}
+
+impl Clone for FlowRef {
+    fn clone(&self) -> FlowRef {
+        unsafe {
+            drop(flow::base(self.get()).ref_count().fetch_add(1, SeqCst));
+            FlowRef {
+                object: raw::TraitObject {
+                    vtable: self.object.vtable,
+                    data: self.object.data,
+                }
+            }
+        }
+    }
+}
+