1 files changed, 52 insertions, 1 deletions

diff --git a/components/script/document_loader.rs b/components/script/document_loader.rs
index e0da74ae706..c6c33fc1a5d 100644
--- a/components/script/document_loader.rs
+++ b/components/script/document_loader.rs
@@ -5,10 +5,13 @@
 //! Tracking of pending loads in a document.
 //! https://html.spec.whatwg.org/multipage/#the-end
 
+use dom::bindings::js::JS;
+use dom::document::Document;
 use msg::constellation_msg::PipelineId;
 use net_traits::AsyncResponseTarget;
 use net_traits::{PendingAsyncLoad, ResourceThread, LoadContext};
 use std::sync::Arc;
+use std::thread;
 use url::Url;
 
 #[derive(JSTraceable, PartialEq, Clone, Debug, HeapSizeOf)]
@@ -41,6 +44,50 @@ impl LoadType {
     }
 }
 
+/// Canary value ensuring that manually added blocking loads (ie. ones that weren't
+/// created via DocumentLoader::prepare_async_load) are always removed by the time
+/// that the owner is destroyed.
+#[derive(JSTraceable, HeapSizeOf)]
+#[must_root]
+pub struct LoadBlocker {
+    /// The document whose load event is blocked by this object existing.
+    doc: JS<Document>,
+    /// The load that is blocking the document's load event.
+    load: Option<LoadType>,
+}
+
+impl LoadBlocker {
+    /// Mark the document's load event as blocked on this new load.
+    pub fn new(doc: &Document, load: LoadType) -> LoadBlocker {
+        doc.add_blocking_load(load.clone());
+        LoadBlocker {
+            doc: JS::from_ref(doc),
+            load: Some(load),
+        }
+    }
+
+    /// Remove this load from the associated document's list of blocking loads.
+    pub fn terminate(blocker: &mut Option<LoadBlocker>) {
+        if let Some(this) = blocker.as_mut() {
+            this.doc.finish_load(this.load.take().unwrap());
+        }
+        *blocker = None;
+    }
+
+    /// Return the url associated with this load.
+    pub fn url(&self) -> Option<&Url> {
+        self.load.as_ref().map(LoadType::url)
+    }
+}
+
+impl Drop for LoadBlocker {
+    fn drop(&mut self) {
+        if !thread::panicking() {
+            assert!(self.load.is_none());
+        }
+    }
+}
+
 #[derive(JSTraceable, HeapSizeOf)]
 pub struct DocumentLoader {
     /// We use an `Arc<ResourceThread>` here in order to avoid file descriptor exhaustion when there
@@ -73,12 +120,16 @@ impl DocumentLoader {
         }
     }
 
+    pub fn add_blocking_load(&mut self, load: LoadType) {
+        self.blocking_loads.push(load);
+    }
+
     /// Create a new pending network request, which can be initiated at some point in
     /// the future.
     pub fn prepare_async_load(&mut self, load: LoadType) -> PendingAsyncLoad {
         let context = load.to_load_context();
         let url = load.url().clone();
-        self.blocking_loads.push(load);
+        self.add_blocking_load(load);
         PendingAsyncLoad::new(context, (*self.resource_thread).clone(), url, self.pipeline)
     }