Dynamically check DOMRefCell access from layout in debug builds

4 files changed, 111 insertions, 5 deletions

diff --git a/components/util/lib.rs b/components/util/lib.rs
index a53f3a1c3d9..0c5c5f65e55 100644
--- a/components/util/lib.rs
+++ b/components/util/lib.rs
@@ -52,6 +52,7 @@ pub mod task;
 pub mod tid;
 pub mod time;
 pub mod taskpool;
+pub mod task_state;
 pub mod vec;
 pub mod workqueue;
 
diff --git a/components/util/task.rs b/components/util/task.rs
index b3e03771610..f286efe5bc3 100644
--- a/components/util/task.rs
+++ b/components/util/task.rs
@@ -8,22 +8,29 @@ use std::comm::Sender;
 use std::task::TaskBuilder;
 use native::task::NativeTaskBuilder;
 
+use task_state;
+
 pub fn spawn_named<S: IntoMaybeOwned<'static>>(name: S, f: proc():Send) {
     let builder = task::TaskBuilder::new().named(name);
     builder.spawn(f);
 }
 
-/// Arrange to send a particular message to a channel if the task built by
-/// this `TaskBuilder` fails.
+/// Arrange to send a particular message to a channel if the task fails.
 pub fn spawn_named_with_send_on_failure<T: Send>(name: &'static str,
+                                                 state: task_state::TaskState,
                                                  f: proc(): Send,
                                                  msg: T,
                                                  dest: Sender<T>,
                                                  native: bool) {
+    let with_state = proc() {
+        task_state::initialize(state);
+        f()
+    };
+
     let future_result = if native {
-        TaskBuilder::new().named(name).native().try_future(f)
+        TaskBuilder::new().named(name).native().try_future(with_state)
     } else {
-        TaskBuilder::new().named(name).try_future(f)
+        TaskBuilder::new().named(name).try_future(with_state)
     };
 
     let watched_name = name.to_string();
diff --git a/components/util/task_state.rs b/components/util/task_state.rs
new file mode 100644
index 00000000000..7c714118b09
--- /dev/null
+++ b/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) { }
+}
diff --git a/components/util/workqueue.rs b/components/util/workqueue.rs
index a9f9419d81c..3a0b3e32f91 100644
--- a/components/util/workqueue.rs
+++ b/components/util/workqueue.rs
@@ -7,6 +7,8 @@
 //! Data associated with queues is simply a pair of unsigned integers. It is expected that a
 //! higher-level API on top of this could allow safe fork-join parallelism.
 
+use task_state;
+
 use native::task::NativeTaskBuilder;
 use rand::{Rng, XorShiftRng};
 use std::mem;
@@ -196,7 +198,10 @@ pub struct WorkQueue<QueueData, WorkData> {
 impl<QueueData: Send, WorkData: Send> WorkQueue<QueueData, WorkData> {
     /// Creates a new work queue and spawns all the threads associated with
     /// it.
-    pub fn new(task_name: &'static str, thread_count: uint, user_data: QueueData) -> WorkQueue<QueueData, WorkData> {
+    pub fn new(task_name: &'static str,
+               state: task_state::TaskState,
+               thread_count: uint,
+               user_data: QueueData) -> WorkQueue<QueueData, WorkData> {
         // Set up data structures.
         let (supervisor_chan, supervisor_port) = channel();
         let (mut infos, mut threads) = (vec!(), vec!());
@@ -231,6 +236,7 @@ impl<QueueData: Send, WorkData: Send> WorkQueue<QueueData, WorkData> {
         // Spawn threads.
         for thread in threads.into_iter() {
             TaskBuilder::new().named(task_name).native().spawn(proc() {
+                task_state::initialize(state | task_state::InWorker);
                 let mut thread = thread;
                 thread.start()
             })