Introduce Pipeline::spawn().

components/constellation/constellation.rs

@@ -406,9 +406,7 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
                     initial_window_size: Option<TypedSize2D<PagePx, f32>>,
                     script_channel: Option<IpcSender<ConstellationControlMsg>>,
                     load_data: LoadData) {
-        let spawning_content = script_channel.is_none();
+        let result = Pipeline::spawn::<Message, LTF, STF>(InitialPipelineState {
-        let (pipeline, unprivileged_pipeline_content, privileged_pipeline_content) =
-            Pipeline::create::<LTF, STF>(InitialPipelineState {
             id: pipeline_id,
             parent_info: parent_info,
             constellation_chan: self.script_sender.clone(),
@@ -431,20 +429,13 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
             webrender_api_sender: self.webrender_api_sender.clone(),
         });
 
-        privileged_pipeline_content.start();
+        let (pipeline, child_process) = match result {
+            Ok(result) => result,
+            Err(e) => return self.handle_send_error(pipeline_id, e),
+        };
 
-        if spawning_content {
+        if let Some(child_process) = child_process {
-            // Spawn the child process.
+            self.child_processes.push(child_process);
-            //
-            // Yes, that's all there is to it!
-            if opts::multiprocess() {
-                match unprivileged_pipeline_content.spawn_multiprocess() {
-                    Ok(child_process) => self.child_processes.push(child_process),
-                    Err(e) => self.handle_send_error(pipeline_id, e),
-                }
-            } else {
-                unprivileged_pipeline_content.start_all::<Message, LTF, STF>(false);
-            }
         }
 
         assert!(!self.pipelines.contains_key(&pipeline_id));

components/constellation/pipeline.rs

@@ -120,9 +120,7 @@ pub struct InitialPipelineState {
 }
 
 impl Pipeline {
-    /// Starts a paint thread, layout thread, and possibly a script thread.
+    fn create<LTF, STF>(state: InitialPipelineState)
-    /// Returns the channels wrapped in a struct.
-    pub fn create<LTF, STF>(state: InitialPipelineState)
                         -> (Pipeline, UnprivilegedPipelineContent, PrivilegedPipelineContent)
         where LTF: LayoutThreadFactory,
               STF: ScriptThreadFactory
@@ -256,6 +254,34 @@ impl Pipeline {
         (pipeline, unprivileged_pipeline_content, privileged_pipeline_content)
     }
 
+    /// Starts a paint thread, layout thread, and possibly a script thread, in
+    /// a new process if requested.
+    pub fn spawn<Message, LTF, STF>(state: InitialPipelineState)
+                                    -> Result<(Pipeline, Option<ChildProcess>), IOError>
+        where LTF: LayoutThreadFactory<Message=Message>,
+              STF: ScriptThreadFactory<Message=Message>
+    {
+        let spawning_content = state.script_chan.is_none();
+        let (pipeline, unprivileged_pipeline_content, privileged_pipeline_content) =
+            Pipeline::create::<LTF, STF>(state);
+
+        privileged_pipeline_content.start();
+
+        let mut child_process = None;
+        if spawning_content {
+            // Spawn the child process.
+            //
+            // Yes, that's all there is to it!
+            if opts::multiprocess() {
+                child_process = Some(try!(unprivileged_pipeline_content.spawn_multiprocess()));
+            } else {
+                unprivileged_pipeline_content.start_all::<Message, LTF, STF>(false);
+            }
+        }
+
+        Ok((pipeline, child_process))
+    }
+
     fn new(id: PipelineId,
            parent_info: Option<(PipelineId, SubpageId, FrameType)>,
            script_chan: IpcSender<ConstellationControlMsg>,
@@ -520,7 +546,7 @@ impl UnprivilegedPipelineContent {
     }
 }
 
-pub struct PrivilegedPipelineContent {
+struct PrivilegedPipelineContent {
     id: PipelineId,
     compositor_proxy: Box<CompositorProxy + Send + 'static>,
     font_cache_thread: FontCacheThread,