generic_channel: Preserve IPC errors (#38854)

We should not be using `route_ipc_receiver_to_new_crossbeam_receiver` or
similar methods, that `unwrap()` on the ROUTER thread if they encounter
IPC errors. Instead, we now propagate the error to the crossbeam
receiver.
In the GenericChannel::Crossbeam case this means, that we need to use a
`Result<T>` as the data type, even though the Result variant is always
okay, so that the receiver type is the same regardless of `IPC` or not.
This is required, so we have the same channel type, and can pass the
inner crossbeam channel into e.g. `select!`, without having to wrap or
re-implement select.

This also means, that as we switch towards GenericChannel, we will
gradually improve our error handling and eventually remove the existing
panics on IPC errors.

These changes were extracted out of
https://github.com/servo/servo/pull/38782

Testing: Covered by existing tests. No new panics were introduced.

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

components/webgl/Cargo.toml

@@ -16,6 +16,7 @@ webgl_backtrace = ["canvas_traits/webgl_backtrace"]
 webxr = ["dep:webxr", "dep:webxr-api"]
 
 [dependencies]
+base = { path = "../shared/base" }
 bitflags = { workspace = true }
 byteorder = { workspace = true }
 canvas_traits = { workspace = true }

components/webgl/webgl_thread.rs

@@ -8,6 +8,7 @@ use std::rc::Rc;
 use std::sync::{Arc, Mutex};
 use std::{slice, thread};
 
+use base::generic_channel::RoutedReceiver;
 use bitflags::bitflags;
 use byteorder::{ByteOrder, NativeEndian, WriteBytesExt};
 use canvas_traits::webgl;
@@ -217,7 +218,7 @@ pub(crate) struct WebGLThread {
     /// We use it to get an unique ID for new WebGLContexts.
     external_images: Arc<Mutex<WebrenderExternalImageRegistry>>,
     /// The receiver that will be used for processing WebGL messages.
-    receiver: crossbeam_channel::Receiver<WebGLMsg>,
+    receiver: RoutedReceiver<WebGLMsg>,
     /// The receiver that should be used to send WebGL messages for processing.
     sender: WebGLSender<WebGLMsg>,
     /// The swap chains used by webrender
@@ -275,7 +276,7 @@ impl WebGLThread {
             bound_context_id: None,
             external_images,
             sender,
-            receiver: receiver.into_inner(),
+            receiver: receiver.route_preserving_errors(),
             webrender_swap_chains,
             api_type,
             #[cfg(feature = "webxr")]
@@ -297,7 +298,7 @@ impl WebGLThread {
 
     fn process(&mut self) {
         let webgl_chan = WebGLChan(self.sender.clone());
-        while let Ok(msg) = self.receiver.recv() {
+        while let Ok(Ok(msg)) = self.receiver.recv() {
             let exit = self.handle_msg(msg, &webgl_chan);
             if exit {
                 break;