introduce a pipeline namespace installer

components/constellation/constellation.rs

@@ -129,7 +129,9 @@ use msg::constellation_msg::{
     BrowsingContextGroupId, BrowsingContextId, HistoryStateId, PipelineId,
     TopLevelBrowsingContextId,
 };
-use msg::constellation_msg::{PipelineNamespace, PipelineNamespaceId, TraversalDirection};
+use msg::constellation_msg::{
+    PipelineNamespace, PipelineNamespaceId, PipelineNamespaceRequest, TraversalDirection,
+};
 use net_traits::pub_domains::reg_host;
 use net_traits::request::RequestBuilder;
 use net_traits::storage_thread::{StorageThreadMsg, StorageType};
@@ -217,6 +219,12 @@ struct BrowsingContextGroup {
 /// the `script` crate). Script and layout communicate using a `Message`
 /// type.
 pub struct Constellation<Message, LTF, STF> {
+    /// An ipc-sender/threaded-receiver pair
+    /// to facilitate installing pipeline namespaces in threads
+    /// via a per-process installer.
+    namespace_receiver: Receiver<Result<PipelineNamespaceRequest, IpcError>>,
+    namespace_sender: IpcSender<PipelineNamespaceRequest>,
+
     /// An IPC channel for script threads to send messages to the constellation.
     /// This is the script threads' view of `script_receiver`.
     script_sender: IpcSender<(PipelineId, FromScriptMsg)>,
@@ -672,6 +680,12 @@ where
                 let script_receiver =
                     route_ipc_receiver_to_new_mpsc_receiver_preserving_errors(ipc_script_receiver);
 
+                let (namespace_sender, ipc_namespace_receiver) =
+                    ipc::channel().expect("ipc channel failure");
+                let namespace_receiver = route_ipc_receiver_to_new_mpsc_receiver_preserving_errors(
+                    ipc_namespace_receiver,
+                );
+
                 let (background_hang_monitor_sender, ipc_bhm_receiver) =
                     ipc::channel().expect("ipc channel failure");
                 let background_hang_monitor_receiver =
@@ -709,6 +723,8 @@ where
                 PipelineNamespace::install(PipelineNamespaceId(1));
 
                 let mut constellation: Constellation<Message, LTF, STF> = Constellation {
+                    namespace_receiver,
+                    namespace_sender,
                     script_sender: ipc_script_sender,
                     background_hang_monitor_sender,
                     background_hang_monitor_receiver,
@@ -987,6 +1003,8 @@ where
                 sender: self.script_sender.clone(),
                 pipeline_id: pipeline_id,
             },
+            namespace_request_sender: self.namespace_sender.clone(),
+            pipeline_namespace_id: self.next_pipeline_namespace_id(),
             background_monitor_register: self.background_monitor_register.clone(),
             background_hang_monitor_to_constellation_chan: self
                 .background_hang_monitor_sender
@@ -1005,7 +1023,6 @@ where
             event_loop,
             load_data,
             device_pixel_ratio: self.window_size.device_pixel_ratio,
-            pipeline_namespace_id: self.next_pipeline_namespace_id(),
             prev_visibility: is_visible,
             webrender_api_sender: self.webrender_api_sender.clone(),
             webrender_document: self.webrender_document,
@@ -1155,6 +1172,7 @@ where
     fn handle_request(&mut self) {
         #[derive(Debug)]
         enum Request {
+            PipelineNamespace(PipelineNamespaceRequest),
             Script((PipelineId, FromScriptMsg)),
             BackgroundHangMonitor(HangMonitorAlert),
             Compositor(FromCompositorMsg),
@@ -1175,6 +1193,9 @@ where
         // being called. If this happens, there's not much we can do
         // other than panic.
         let request = select! {
+            recv(self.namespace_receiver) -> msg => {
+                msg.expect("Unexpected script channel panic in constellation").map(Request::PipelineNamespace)
+            }
             recv(self.script_receiver) -> msg => {
                 msg.expect("Unexpected script channel panic in constellation").map(Request::Script)
             }
@@ -1203,6 +1224,9 @@ where
         };
 
         match request {
+            Request::PipelineNamespace(message) => {
+                self.handle_request_for_pipeline_namespace(message)
+            },
             Request::Compositor(message) => self.handle_request_from_compositor(message),
             Request::Script(message) => {
                 self.handle_request_from_script(message);
@@ -1222,6 +1246,11 @@ where
         }
     }
 
+    fn handle_request_for_pipeline_namespace(&mut self, request: PipelineNamespaceRequest) {
+        let PipelineNamespaceRequest(sender) = request;
+        let _ = sender.send(self.next_pipeline_namespace_id());
+    }
+
     fn handle_request_from_background_hang_monitor(&self, message: HangMonitorAlert) {
         match message {
             HangMonitorAlert::Profile(bytes) => self

components/constellation/pipeline.rs

@@ -22,7 +22,10 @@ use media::WindowGLContext;
 use metrics::PaintTimeMetrics;
 use msg::constellation_msg::TopLevelBrowsingContextId;
 use msg::constellation_msg::{BackgroundHangMonitorRegister, HangMonitorAlert, SamplerControlMsg};
-use msg::constellation_msg::{BrowsingContextId, HistoryStateId, PipelineId, PipelineNamespaceId};
+use msg::constellation_msg::{BrowsingContextId, HistoryStateId};
+use msg::constellation_msg::{
+    PipelineId, PipelineNamespace, PipelineNamespaceId, PipelineNamespaceRequest,
+};
 use net::image_cache::ImageCacheImpl;
 use net_traits::image_cache::ImageCache;
 use net_traits::{IpcSend, ResourceThreads};
@@ -121,6 +124,9 @@ pub struct InitialPipelineState {
     /// A channel to the associated constellation.
     pub script_to_constellation_chan: ScriptToConstellationChan,
 
+    /// A sender to request pipeline namespace ids.
+    pub namespace_request_sender: IpcSender<PipelineNamespaceRequest>,
+
     /// A handle to register components for hang monitoring.
     /// None when in multiprocess mode.
     pub background_monitor_register: Option<Box<dyn BackgroundHangMonitorRegister>>,
@@ -164,15 +170,15 @@ pub struct InitialPipelineState {
     /// Information about the device pixel ratio.
     pub device_pixel_ratio: Scale<f32, CSSPixel, DevicePixel>,
 
+    /// The ID of the pipeline namespace for this script thread.
+    pub pipeline_namespace_id: PipelineNamespaceId,
+
     /// The event loop to run in, if applicable.
     pub event_loop: Option<Rc<EventLoop>>,
 
     /// Information about the page to load.
     pub load_data: LoadData,
 
-    /// The ID of the pipeline namespace for this script thread.
-    pub pipeline_namespace_id: PipelineNamespaceId,
-
     /// Whether the browsing context in which pipeline is embedded is visible
     /// for the purposes of scheduling and resource management. This field is
     /// only used to notify script and compositor threads after spawning
@@ -278,6 +284,7 @@ impl Pipeline {
                     parent_pipeline_id: state.parent_pipeline_id,
                     opener: state.opener,
                     script_to_constellation_chan: state.script_to_constellation_chan.clone(),
+                    namespace_request_sender: state.namespace_request_sender,
                     background_hang_monitor_to_constellation_chan: state
                         .background_hang_monitor_to_constellation_chan
                         .clone(),
@@ -484,6 +491,7 @@ pub struct UnprivilegedPipelineContent {
     browsing_context_id: BrowsingContextId,
     parent_pipeline_id: Option<PipelineId>,
     opener: Option<BrowsingContextId>,
+    namespace_request_sender: IpcSender<PipelineNamespaceRequest>,
     script_to_constellation_chan: ScriptToConstellationChan,
     background_hang_monitor_to_constellation_chan: IpcSender<HangMonitorAlert>,
     sampling_profiler_port: Option<IpcReceiver<SamplerControlMsg>>,
@@ -522,6 +530,10 @@ impl UnprivilegedPipelineContent {
         LTF: LayoutThreadFactory<Message = Message>,
         STF: ScriptThreadFactory<Message = Message>,
     {
+        // Setup pipeline-namespace-installing for all threads in this process.
+        // Idempotent in single-process mode.
+        PipelineNamespace::set_installer_sender(self.namespace_request_sender);
+
         let image_cache = Arc::new(ImageCacheImpl::new(self.webrender_api_sender.create_api()));
         let paint_time_metrics = PaintTimeMetrics::new(
             self.id,

components/msg/Cargo.toml

@@ -13,8 +13,11 @@ test = false
 doctest = false
 
 [dependencies]
+lazy_static = "1"
+ipc-channel = "0.11"
 malloc_size_of = { path = "../malloc_size_of" }
 malloc_size_of_derive = "0.1"
+parking_lot = "0.8"
 serde = "1.0.60"
 webrender_api = {git = "https://github.com/servo/webrender", features = ["ipc"]}
 

components/msg/constellation_msg.rs

@@ -5,10 +5,13 @@
 //! The high-level interface from script to constellation. Using this abstract interface helps
 //! reduce coupling between these two components.
 
+use ipc_channel::ipc::{self, IpcReceiver, IpcSender};
+use parking_lot::Mutex;
 use std::cell::Cell;
 use std::fmt;
 use std::mem;
 use std::num::NonZeroU32;
+use std::sync::Arc;
 use std::time::Duration;
 
 #[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, PartialEq, Serialize)]
@@ -17,12 +20,71 @@ pub enum TraversalDirection {
     Back(usize),
 }
 
+#[derive(Debug, Deserialize, Serialize)]
+/// Request a pipeline-namespace id from the constellation.
+pub struct PipelineNamespaceRequest(pub IpcSender<PipelineNamespaceId>);
+
+/// A per-process installer of pipeline-namespaces.
+pub struct PipelineNamespaceInstaller {
+    request_sender: Option<IpcSender<PipelineNamespaceRequest>>,
+    namespace_sender: IpcSender<PipelineNamespaceId>,
+    namespace_receiver: IpcReceiver<PipelineNamespaceId>,
+}
+
+impl PipelineNamespaceInstaller {
+    pub fn new() -> Self {
+        let (namespace_sender, namespace_receiver) =
+            ipc::channel().expect("PipelineNamespaceInstaller ipc channel failure");
+        PipelineNamespaceInstaller {
+            request_sender: None,
+            namespace_sender: namespace_sender,
+            namespace_receiver: namespace_receiver,
+        }
+    }
+
+    /// Provide a request sender to send requests to the constellation.
+    pub fn set_sender(&mut self, sender: IpcSender<PipelineNamespaceRequest>) {
+        self.request_sender = Some(sender);
+    }
+
+    /// Install a namespace, requesting a new Id from the constellation.
+    pub fn install_namespace(&self) {
+        match self.request_sender.as_ref() {
+            Some(sender) => {
+                let _ = sender.send(PipelineNamespaceRequest(self.namespace_sender.clone()));
+                let namespace_id = self
+                    .namespace_receiver
+                    .recv()
+                    .expect("The constellation to make a pipeline namespace id available");
+                PipelineNamespace::install(namespace_id);
+            },
+            None => unreachable!("PipelineNamespaceInstaller should have a request_sender setup"),
+        }
+    }
+}
+
+lazy_static! {
+    /// A per-process unique pipeline-namespace-installer.
+    /// Accessible via PipelineNamespace.
+    ///
+    /// Use PipelineNamespace::set_installer_sender to initiate with a sender to the constellation,
+    /// when a new process has been created.
+    ///
+    /// Use PipelineNamespace::fetch_install to install a unique pipeline-namespace from the calling thread.
+    static ref PIPELINE_NAMESPACE_INSTALLER: Arc<Mutex<PipelineNamespaceInstaller>> =
+        Arc::new(Mutex::new(PipelineNamespaceInstaller::new()));
+}
+
 /// Each pipeline ID needs to be unique. However, it also needs to be possible to
 /// generate the pipeline ID from an iframe element (this simplifies a lot of other
 /// code that makes use of pipeline IDs).
 ///
 /// To achieve this, each pipeline index belongs to a particular namespace. There is
 /// a namespace for the constellation thread, and also one for every script thread.
+///
+/// A namespace can be installed for any other thread in a process
+/// where an pipeline-installer has been initialized.
+///
 /// This allows pipeline IDs to be generated by any of those threads without conflicting
 /// with pipeline IDs created by other script threads or the constellation. The
 /// constellation is the only code that is responsible for creating new *namespaces*.
@@ -39,6 +101,7 @@ pub struct PipelineNamespace {
 }
 
 impl PipelineNamespace {
+    /// Install a namespace for a given Id.
     pub fn install(namespace_id: PipelineNamespaceId) {
         PIPELINE_NAMESPACE.with(|tls| {
             assert!(tls.get().is_none());
@@ -49,6 +112,25 @@ impl PipelineNamespace {
         });
     }
 
+    /// Setup the pipeline-namespace-installer, by providing it with a sender to the constellation.
+    /// Idempotent in single-process mode.
+    pub fn set_installer_sender(sender: IpcSender<PipelineNamespaceRequest>) {
+        PIPELINE_NAMESPACE_INSTALLER.lock().set_sender(sender);
+    }
+
+    /// Install a namespace in the current thread, without requiring having a namespace Id ready.
+    /// Panics if called more than once per thread.
+    pub fn auto_install() {
+        // Note that holding the lock for the duration of the call is irrelevant to performance,
+        // since a thread would have to block on the ipc-response from the constellation,
+        // with the constellation already acting as a global lock on namespace ids,
+        // and only being able to handle one request at a time.
+        //
+        // Hence, any other thread attempting to concurrently install a namespace
+        // would have to wait for the current call to finish, regardless of the lock held here.
+        PIPELINE_NAMESPACE_INSTALLER.lock().install_namespace();
+    }
+
     fn next_index(&mut self) -> NonZeroU32 {
         self.index += 1;
         NonZeroU32::new(self.index).expect("pipeline id index wrapped!")

components/msg/lib.rs

@@ -4,6 +4,8 @@
 
 #![deny(unsafe_code)]
 
+#[macro_use]
+extern crate lazy_static;
 #[macro_use]
 extern crate malloc_size_of;
 #[macro_use]

components/script/dom/workerglobalscope.rs

@@ -44,7 +44,7 @@ use js::jsapi::JSAutoRealm;
 use js::jsval::UndefinedValue;
 use js::panic::maybe_resume_unwind;
 use js::rust::{HandleValue, ParentRuntime};
-use msg::constellation_msg::PipelineId;
+use msg::constellation_msg::{PipelineId, PipelineNamespace};
 use net_traits::request::{
     CredentialsMode, Destination, ParserMetadata, RequestBuilder as NetRequestInit,
 };
@@ -123,6 +123,8 @@ impl WorkerGlobalScope {
         timer_event_chan: IpcSender<TimerEvent>,
         closing: Option<Arc<AtomicBool>>,
     ) -> Self {
+        // Install a pipeline-namespace in the current thread.
+        PipelineNamespace::auto_install();
         Self {
             globalscope: GlobalScope::new_inherited(
                 init.pipeline_id,