net: Start reducing number of IPCs channels used for fetch with a FetchThread (#33863)

Instead of creating a `ROUTER` for each fetch, create a fetch thread
which handles all incoming and outcoming fetch requests. Now messages
involving fetches carry a "request id" which indicates which fetch is
being addressed by the message. This greatly reduces the number of file
descriptors used by fetch.

In addition, the interface for kicking off fetches is simplified when
using the `Listener` with `Document`s and the `GlobalScope`.

This does not fix all leaked file descriptors / mach ports, but greatly
eliminates the number used. Now tests can be run without limiting
procesess on modern macOS systems.

Followup work:

1. There are more instances where fetch is done using the old method.
   Some of these require more changes in order to be converted to the
   `FetchThread` approach.
2. Eliminate usage of IPC channels when doing redirects.
3. Also eliminate the IPC channel used for cancel handling.
4. This change opens up the possiblity of controlling the priority of
   fetch requests.

Fixes #29834.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/htmlmediaelement.rs

@@ -21,10 +21,10 @@ use ipc_channel::ipc::{self, IpcSharedMemory};
 use ipc_channel::router::ROUTER;
 use js::jsapi::JSAutoRealm;
 use media::{glplayer_channel, GLPlayerMsg, GLPlayerMsgForward, WindowGLContext};
-use net_traits::request::Destination;
+use net_traits::request::{Destination, RequestId};
 use net_traits::{
-    CoreResourceMsg, FetchChannels, FetchMetadata, FetchResponseListener, Metadata, NetworkError,
-    ResourceFetchTiming, ResourceTimingType,
+    FetchMetadata, FetchResponseListener, Metadata, NetworkError, ResourceFetchTiming,
+    ResourceTimingType,
 };
 use pixels::Image;
 use script_layout_interface::HTMLMediaData;
@@ -101,7 +101,7 @@ use crate::dom::videotracklist::VideoTrackList;
 use crate::dom::virtualmethods::VirtualMethods;
 use crate::fetch::{create_a_potential_cors_request, FetchCanceller};
 use crate::microtask::{Microtask, MicrotaskRunnable};
-use crate::network_listener::{self, NetworkListener, PreInvoke, ResourceTimingListener};
+use crate::network_listener::{self, PreInvoke, ResourceTimingListener};
 use crate::realms::{enter_realm, InRealm};
 use crate::script_runtime::CanGc;
 use crate::script_thread::ScriptThread;
@@ -890,36 +890,12 @@ impl HTMLMediaElement {
         }
         let (fetch_context, cancel_receiver) = HTMLMediaElementFetchContext::new();
         *current_fetch_context = Some(fetch_context);
-        let fetch_listener = Arc::new(Mutex::new(HTMLMediaElementFetchListener::new(
-            self,
-            url.clone(),
-            offset.unwrap_or(0),
-            seek_lock,
-        )));
-        let (action_sender, action_receiver) = ipc::channel().unwrap();
-        let window = window_from_node(self);
-        let (task_source, canceller) = window
-            .task_manager()
-            .networking_task_source_with_canceller();
-        let network_listener = NetworkListener {
-            context: fetch_listener,
-            task_source,
-            canceller: Some(canceller),
-        };
-        ROUTER.add_route(
-            action_receiver.to_opaque(),
-            Box::new(move |message| {
-                network_listener.notify_fetch(message.to().unwrap());
-            }),
-        );
-        let global = self.global();
-        global
-            .core_resource_thread()
-            .send(CoreResourceMsg::Fetch(
-                request,
-                FetchChannels::ResponseMsg(action_sender, Some(cancel_receiver)),
-            ))
-            .unwrap();
+        let listener =
+            HTMLMediaElementFetchListener::new(self, url.clone(), offset.unwrap_or(0), seek_lock);
+
+        // TODO: If this is supposed to to be a "fetch" as defined in the specification
+        // this should probably be integrated into the Document's list of cancellable fetches.
+        document_from_node(self).fetch_background(request, listener, Some(cancel_receiver));
     }
 
     // https://html.spec.whatwg.org/multipage/#concept-media-load-resource
@@ -2681,11 +2657,11 @@ struct HTMLMediaElementFetchListener {
 
 // https://html.spec.whatwg.org/multipage/#media-data-processing-steps-list
 impl FetchResponseListener for HTMLMediaElementFetchListener {
-    fn process_request_body(&mut self) {}
+    fn process_request_body(&mut self, _: RequestId) {}
 
-    fn process_request_eof(&mut self) {}
+    fn process_request_eof(&mut self, _: RequestId) {}
 
-    fn process_response(&mut self, metadata: Result<FetchMetadata, NetworkError>) {
+    fn process_response(&mut self, _: RequestId, metadata: Result<FetchMetadata, NetworkError>) {
         let elem = self.elem.root();
 
         if elem.generation_id.get() != self.generation_id || elem.player.borrow().is_none() {
@@ -2759,7 +2735,7 @@ impl FetchResponseListener for HTMLMediaElementFetchListener {
         }
     }
 
-    fn process_response_chunk(&mut self, payload: Vec<u8>) {
+    fn process_response_chunk(&mut self, _: RequestId, payload: Vec<u8>) {
         let elem = self.elem.root();
         // If an error was received previously or if we triggered a new fetch request,
         // we skip processing the payload.
@@ -2818,7 +2794,11 @@ impl FetchResponseListener for HTMLMediaElementFetchListener {
     }
 
     // https://html.spec.whatwg.org/multipage/#media-data-processing-steps-list
-    fn process_response_eof(&mut self, status: Result<ResourceFetchTiming, NetworkError>) {
+    fn process_response_eof(
+        &mut self,
+        _: RequestId,
+        status: Result<ResourceFetchTiming, NetworkError>,
+    ) {
         trace!("process response eof");
         if let Some(seek_lock) = self.seek_lock.take() {
             seek_lock.unlock(/* successful seek */ false);