Dynamically check DOMRefCell access from layout in debug builds

components/util/task_state.rs

@@ -0,0 +1,92 @@
+/* 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/. */
+
+//! Supports dynamic assertions in debug builds about what sort of task is
+//! running and what state it's in.
+//!
+//! In release builds, `get` is not available; calls must be inside
+//! `debug_assert!` or similar.  All of the other functions inline away to
+//! nothing.
+
+pub use self::imp::{initialize, enter, exit};
+
+#[cfg(not(ndebug))]
+pub use self::imp::get;
+
+bitflags! {
+    #[deriving(Show)]
+    flags TaskState: u32 {
+        static Script        = 0x01,
+        static Layout        = 0x02,
+        static Render        = 0x04,
+
+        static InWorker      = 0x0100,
+    }
+}
+
+// Exactly one of these should be set.
+static task_types: &'static [TaskState]
+    = &[Script, Layout, Render];
+
+macro_rules! predicates ( ( $( $f:ident = $c:ident ; )* ) => (
+    impl TaskState {
+        $(
+            pub fn $f(self) -> bool {
+                self.contains($c)
+            }
+        )*
+    }
+))
+
+predicates! {
+    is_script = Script;
+    is_layout = Layout;
+    is_render = Render;
+}
+
+#[cfg(not(ndebug))]
+mod imp {
+    use super::{TaskState, task_types};
+
+    local_data_key!(STATE: TaskState)
+
+    pub fn initialize(x: TaskState) {
+        match STATE.replace(Some(x)) {
+            None => (),
+            Some(s) => fail!("Task state already initialized as {}", s),
+        };
+        get(); // check the assertion below
+    }
+
+    pub fn get() -> TaskState {
+        let state = match STATE.get() {
+            None => fail!("Task state not initialized"),
+            Some(s) => *s,
+        };
+
+        // Exactly one of the task type flags should be set.
+        assert_eq!(1, task_types.iter().filter(|&&ty| state.contains(ty)).count());
+        state
+    }
+
+    pub fn enter(x: TaskState) {
+        let state = get();
+        assert!(!state.intersects(x));
+        STATE.replace(Some(state | x));
+    }
+
+    pub fn exit(x: TaskState) {
+        let state = get();
+        assert!(state.contains(x));
+        STATE.replace(Some(state & !x));
+    }
+}
+
+#[cfg(ndebug)]
+mod imp {
+    use super::TaskState;
+    #[inline(always)] pub fn initialize(_: TaskState) { }
+    #[inline(always)] pub fn enter(_: TaskState) { }
+    #[inline(always)] pub fn exit(_: TaskState) { }
+}